Disease: Flu
(Influenza)

    Flu (influenza, conventional, H1N1, H3N2, and bird flu [H5N1]) facts

    • Influenza, commonly called "the flu," is caused by viruses that infect the respiratory tract.
    • Influenza viruses are divided into three types, designated A, B, and C, with influenza A types usually causing the most problems in humans.
    • Most people who get the conventional or seasonal flu recover completely in one to two weeks, but some people develop serious and potentially life-threatening medical complications, such as pneumonia.
    • Much of the illness and death caused by conventional or seasonal influenza can be prevented by annual influenza vaccination.
    • Influenza A undergoes frequent antigenic changes that require new vaccines to be developed and people to obtain a new vaccination every year. New vaccine technology is being developed.
    • In April 2009, a new flu virus termed novel H1N1 swine flu developed in Mexico, rapidly spread worldwide, and caused the WHO to declare a flu pandemic. Eventually, the WHO declared the pandemic over in 2010. In 2012, a new type of flu strain developed, H3N2v, but has not developed into any epidemic situations currently.
    • Like the influenza virus, drug treatments are constantly changing and improving, but currently, timely vaccination is still considered to be the best defense against the flu. However, the CDC considers antivirals an important adjunct to the flu vaccine in the control of the disease process.
    • People should be aware that flu pandemics can cause severe flu symptoms and sometimes cause death in many individuals who may be more susceptible to the pandemic flu than the conventional flu; however, the previous pandemic flu virus (H1N1) has been available in vaccines and is considered part of the conventional circulating flu viruses.
    • Bird flu (H5N1) mainly infects birds but it also infects humans who have close contacts with birds.
    • Individuals should check with their doctors to determine if they are considered to be at higher risk of getting severe flu symptoms than the normally healthy population.
    Picture of the influenza virus

    What is flu (influenza)?

    Influenza, commonly called "the flu," is an illness caused by RNA viruses that infect the respiratory tract of many animals, birds, and humans. In most people, the infection results in the person getting a fever, cough, headache, and malaise (tired, no energy); some people also may develop a sore throat, nausea, vomiting, and diarrhea. The majority of individuals has symptoms for about one to two weeks and then recovers with no problems. However, compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection can cause a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus.

    The above is the usual situation for the yearly occurring "conventional" or "seasonal" flu strains. However, there are situations in which some flu outbreaks are severe. These severe outbreaks occur when a portion of the human population is exposed to a flu strain against which the population has little or no immunity because the virus has become altered in a significant way. These outbreaks are usually termed epidemics. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last hundred years since influenza virus was identified in 1933. By an examination of preserved tissue, the worst influenza pandemic (also termed the Spanish flu or Spanish influenza) occurred in 1918 when the virus caused between 40-100 million deaths worldwide, with a mortality rate estimated to range from 2%-20%.

    In April 2009, a new influenza strain against which the world population has little or no immunity was isolated from humans in Mexico. It quickly spread throughout the world so fast that the WHO declared this new flu strain (first termed novel H1N1 influenza A swine flu, often later shortened to H1N1 or swine flu) as the cause of a pandemic on June 11, 2009. This was the first declared flu pandemic in 41 years. Fortunately, there was a worldwide response that included vaccine production, good hygiene practices (especially hand washing) were emphasized, and the virus (H1N1) caused far less morbidity and mortality than was expected and predicted. The WHO declared the pandemic's end on Aug. 10, 2010, because it no longer fit into the WHO's criteria for a pandemic.

    A new influenza strain, H3N2, was identified in 2011, but this strain has caused only about 330 infections with one death in the U.S. Another strain, H5N1, a bird flu virus, has been identified since 2003 and has caused about 650 human infections; this virus has not been detected in the U.S. and currently is not known to be easily spread among people in contrast to other flu strains. Unfortunately, people infected with H5N1 have a high death rate (about 60% of infected people die); currently, H5N1 is not readily transferred from person to person like other flu viruses.

    Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until the virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children, and it occasionally causes ear, eye, sinus, joint, and a few other infections, but it does not cause the flu.

    What are the causes of the flu (influenza)?

    The flu (influenza) viruses

    Influenza viruses cause the flu and are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Influenza type C differs from types A and B in some important ways. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public-health impact of influenza types A and B. Efforts to control the impact of influenza are aimed at types A and B, and the remainder of this discussion will be devoted only to these two types.

    Influenza viruses continually change over time, usually by mutation (change in the viral RNA). This constant changing often enables the virus to evade the immune system of the host (humans, birds, and other animals) so that the host is susceptible to changing influenza virus infections throughout life. This process works as follows: A host infected with influenza virus develops antibodies against that virus; as the virus changes, the "first" antibody no longer recognizes the "newer" virus and infection can occur because the host does not recognize the new flu virus as a problem until the infection is well under way. The first antibody developed may, in some instances, provide partial protection against infection with a new influenza virus. In 2009, almost all individuals had no antibodies that could recognize the novel H1N1 virus immediately.

    Type A viruses are divided into subtypes or strains based on differences in two viral surface proteins called the hemagglutinin (H) and the neuraminidase (N). There are at least 16 known H subtypes and nine known N subtypes. These surface proteins can occur in many combinations. When spread by droplets or direct contact, the virus, if not killed by the host's immune system, replicates in the respiratory tract and damages host cells. In people who are immune compromised (for example, pregnant women, infants, cancer patients, asthma patients, people with pulmonary disease and many others), the virus can cause viral pneumonia or stress the individual's system to make them more susceptible to bacterial infections, especially bacterial pneumonia. Both pneumonia types, viral and bacterial, can cause severe disease and sometimes death.

    Antigenic shift and drift

    Influenza type A viruses undergo two kinds of changes. One is a series of mutations that occurs over time and causes a gradual evolution of the virus. This is called antigenic "drift." The other kind of change is an abrupt change in the hemagglutinin and/or the neuraminidase proteins. This is called antigenic "shift." In this case, a new subtype of the virus suddenly emerges. Type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift and therefore do not cause pandemics.

    The 2009 pandemic-causing H1N1 virus is a classic example of antigenic shift. Research showed that novel H1N1 swine flu has an RNA genome that contains five RNA strands derived from various swine flu strains, two RNA strands from bird flu (also termed avian flu) strains, and only one RNA strand from human flu strains. According to the U.S. Centers for Disease Control and Prevention (CDC), mainly antigenic shifts over about 20 years led to the development of novel H1N1 flu virus. A diagram that illustrates both antigenic shift and drift can be found below (see Figure 2) and features influenza A types H1N1 and bird flu (H5N1), but almost every influenza A viral strain can go through these processes that changes the viral RNA.

    Figure 2. An example of influenza antigenic shift and drift

    What are flu (influenza) symptoms in adults and in children?

    Typical clinical features of influenza may include

    • fever (usually 100 F-103 F in adults and often even higher in children),
    • chills,
    • respiratory symptoms such as
      • cough (more often in adults),
      • sore throat (more often in adults),
      • runny or stuffy nose (especially in children),
    • headache,
    • muscle aches,
    • fatigue, sometimes extreme.

    Although nausea, vomiting, and diarrhea can sometimes accompany influenza infection, especially in children, gastrointestinal symptoms are rarely prominent. The term "stomach flu" is a misnomer that is sometimes used to describe gastrointestinal illnesses caused by other microorganisms. H1N1 infections, however, have caused more nausea, vomiting, and diarrhea than the conventional (seasonal) flu viruses.

    Most individuals who contract influenza recover in a week or two, however, others develop potentially life-threatening complications like pneumonia. In an average year, influenza is associated with about 36,000 deaths nationwide and many more hospitalizations. Flu-related complications can occur at any age; however, the elderly and people with chronic health problems are much more likely to develop serious complications after the conventional influenza infections than are younger, healthier people.

    Unfortunately, people may be contagious about 24-48 hours before symptoms appear and, for those who spontaneously recover, they may shed contagious viruses for about a week.

    How is the flu (influenza) diagnosed?

    The flu is presumptively diagnosed clinically by the patient's history of association with people known to have the disease and their symptoms listed above. Usually, a quick test (for example, nasopharyngeal swab sample) is done to see if the patient is infected with influenza A or B virus. Most of the tests can distinguish between A and B types. The test can be negative (no flu infection) or positive for types A or B. If it is positive for type A, the person could have a conventional flu strain or a potentially more aggressive strain such as H1N1. However, a new test developed by the CDC and a commercial company reportedly can detect H1N1 reliably in about one hour; the test was formerly only available to the military. In 2010, the FDA approved a commercially available test that could detect H1N1 within four hours. Most of the rapid tests are based on PCR technology that identified the genetic material of the virus.

    Swine flu (H1N1) and other influenza strains like bird flu or H3N2 are definitively diagnosed by identifying the particular antigens associated with the virus strain. In general, this testing is done in a specialized laboratory and is not done by many doctors' offices or hospital laboratories unless they have purchased the newest test systems. However, doctors' offices are able to send specimens to specialized laboratories if necessary.

    What is the key to flu (influenza) prevention?

    Flu vaccine

    Most of the illness and death caused by influenza can be prevented by annual influenza vaccination. The CDC's current Advisory Committee on Immunization Practices (ACIP) issued recommendations for everyone 6 months of age and older, who do not have any contraindications to vaccination, to receive a flu vaccine each year.

    Flu vaccine (influenza vaccine made from inactivated and sometimes attenuated [noninfective] virus or virus components) is specifically recommended for those who are at high risk for developing serious complications as a result of influenza infection.

    A new vaccine type, Fluzone Intradermal, was approved by the FDA in 2011 (for adults 18-64 years of age). This injection goes only into the intradermal area of the skin, not into the muscle (IM) like most conventional flu shots, and uses a much smaller needle than the conventional shots. This killed viral preparation is supposed to be about as effective as the IM shot but claims to produce less pain and fewer side effects (see section below).

    Are there any flu shot or nasal spray vaccine side effects in adults or in children?

    Although annual influenza (injectable) vaccination has long been recommended for people in the high-risk groups, many still do not receive the vaccine, often because of their concern about side effects. They mistakenly perceive influenza as merely a nuisance and believe that the vaccine causes unpleasant side effects or that it may even cause the flu. The truth is that influenza vaccine causes no side effects in most people. The most serious side effect that can occur after influenza vaccination is an allergic reaction in people who have a severe allergy to eggs, since the viruses used in the vaccine are grown in hens' eggs. However, a newer form of the vaccine is available that is not grown in chicken eggs. For this reason, people who have an allergy to eggs should not receive the conventional influenza vaccine, but the newer forms may be appropriate for them. Also, the vaccine is not recommended while individuals have active infections or active diseases of the nervous system. Less than one-third of those who receive the vaccine have some soreness at the vaccination site, and about 5%-10% experience mild side effects, such as headache, low-grade fever, or muscle cramps, for about a day after vaccination. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past. The intradermal shots reportedly have similar side effects as the IM shot but are less intense and may not last as long as the IM shot.

    Nevertheless, some older people remember earlier influenza vaccines that did, in fact, produce more unpleasant side effects. Vaccines produced from the 1940s to the mid-1960s were not as highly purified as modern influenza vaccines, and it was these impurities that caused most of the side effects. Since the side effects associated with these early vaccines, such as fever, headache, muscle aches, and fatigue, were similar to some of the symptoms of influenza, people believed that the vaccine had caused them to get the flu. However, injectable influenza vaccine produced in the United States has never been capable of causing influenza because it consists of killed virus.

    Another type of influenza vaccine (nasal spray) is made with live attenuated (altered) influenza viruses. This vaccine is made with live viruses that can stimulate the immune response enough to confer immunity but do not cause classic influenza symptoms (in most instances). The nasal spray vaccine (Flumist) is only approved for healthy individuals ages 2-49 years of age and is recommended preferentially for healthy children aged 2 through 8 who do not have contraindications to receiving the vaccine, if it is readily available. This nasal spray vaccine contains live attenuated virus (less able to cause flu symptoms due to a designed inability to replicate at normal body temperatures). This live vaccine could possibly cause the disease in infants and immunocompromised people and does not produce a strong immune response in many older people. Side effects of the nasal spray vaccine include nasal congestion, sore throat, and fever. Headaches, muscle aches, irritability, and malaise have also been noted. In most instances, if side effects occur, they only last a day or two. This nasal spray has been produced for conventional flu viruses and should not be given to pregnant women or anyone who has a medical condition that may compromise the immune system because in some instances the flu may be a side effect.

    Some people do not receive influenza vaccine because they believe it is not very effective. There are several different reasons for this belief. People who have received influenza vaccine may subsequently have an illness that is mistaken for influenza, and they believe that the vaccine failed to protect them. In other cases, people who have received the vaccine may indeed have an influenza infection. Overall vaccine effectiveness varies from year to year, depending upon the degree of similarity between the influenza virus strains included in the vaccine and the strain or strains that circulate during the influenza season. Because the vaccine strains must be chosen nine to 10 months before the influenza season, and because influenza viruses mutate over time, sometimes mutations occur in the circulating virus strains between the time the vaccine strains are chosen and the next influenza season ends. These mutations sometimes reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby reducing vaccine efficacy. This commonly occurs with the conventional flu vaccines as the specific virus types chosen for vaccine inclusion are based on reasoned projections for the upcoming flu season. Occasionally, the vaccine does not match the actual predominating virus strain and is not very effective in generating a specific immune response to the predominant infecting flu strain.

    Vaccine efficacy also varies from one person to another. Studies of healthy young adults have shown influenza vaccine to be 70%-90% effective in preventing illness. In the elderly and those with certain chronic medical conditions such as HIV, the vaccine is often less effective in preventing illness. Studies show the vaccine reduces hospitalization by about 70% and death by about 85% among the elderly who are not in nursing homes. Among nursing-home residents, vaccine can reduce the risk of hospitalization by about 50%, the risk of pneumonia by about 60%, and the risk of death by 75%-80%. If antigenic drift results in changing the circulating virus from the strains used in the vaccine, vaccine efficacy may be reduced. However, the vaccine is still likely to lessen the severity of the illness and to prevent complications and death.

    Recent studies suggest that in younger children (ages 2-8) the nasal spray flu vaccine may prevent about 50% more cases of flu than the vaccine administered by the flu shot. Therefore, children in this age group who have no contraindications should receive this form of the vaccine if it is available. However, the CDC recommends that vaccination not be delayed if this form is not available; the flu shot should be given in this case.

    Why should the flu (influenza) vaccine be taken every year?

    Although only a few different influenza virus strains circulate at any given time, people may continue to become ill with the flu throughout their lives. The reason for this continuing susceptibility is that influenza viruses are continually mutating, through the mechanisms of antigenic shift and drift described above. Each year, the vaccine is updated to include the most current influenza virus strains that are infecting people worldwide. The fact that influenza viral genes continually change is one of the reasons vaccine must be taken every year. Another reason is that antibody produced by the host in response to the vaccine declines over time, and antibody levels are often low one year after vaccination so even if the same vaccine is used, it can act as a booster shot to raise immunity.

    Because of the vaccine synthesis and distribution problems with the pandemic H1N1 vaccines, a number of companies have begun development of new vaccine synthesis technologies to avoid the variable production quantities of virus and the long growth cycle and purification process in chicken eggs. There are at least five new technologically novel approaches under development (recombinant protein, virus-like particle synthesis, viral vectors, DNA-based vaccines [altered plasmids] and viral vectors that contain specific antigens). The CDC has indicated they plan to overhaul their vaccine distribution system, especially for those instances when a pandemic strain arises. Several vaccines have undergone clinical trials and have been approved for use.

    Many people still refuse to get flu shots because of misunderstandings, fear, "because I never get any shots," or simply a belief that if they get the flu, they will do well. These are only some of the reasons -- there are many more. The U.S. and other countries populations need to be better educated about vaccines; at least they should realize that safe vaccines have been around for many years (measles, mumps, chickenpox, and even a vaccine for cholera), and as adults they often have to get a vaccine-like shot to test for tuberculosis exposure or to protect themselves from tetanus. The flu vaccines are as safe as these vaccines and shots that are widely accepted by the public. Consequently, better efforts need to be made to make yearly flu vaccines as widely acceptable as other vaccines. Susceptible people need to understand that the vaccines afford them a significant chance to reduce or prevent this potentially debilitating disease, hospitalization and, in a few, a lethal flu-caused disease.

    What are some flu treatments an individual can do at home?

    First, individuals should be sure they are not members of a high-risk group that is more susceptible to getting severe flu symptoms. Check with your physician if you are unsure if you are a higher-risk person. Home care is recommended by the CDC if a person is normally healthy with no underlying diseases or conditions (for example, asthma, lung disease, pregnant, or immunosuppressed).

    Increasing liquid intake, warm showers, and warm compresses, especially in the nasal area, can reduce the body aches and reduce nasal congestion. Nasal strips and humidifiers may help reduce congestion, especially while trying to sleep. Some physicians recommend nasal irrigation with saline to further reduce congestion; some recommend nonprescription decongestants. Fever can be treated with over-the-counter acetaminophen (Tylenol) or ibuprofen (Motrin and others); read labels for safe dosage. Cough can be suppressed by cough drops and over-the-counter cough syrup. If an individual's symptoms at home get worse, their doctor should be notified.

    Learn more about: Tylenol

    When should a person go to the emergency department for the flu?

    The CDC urges people to seek emergency medical care for a sick child with any of these symptoms:

    1. Fast breathing or trouble breathing
    2. Bluish or gray skin color
    3. Not drinking enough fluids
    4. Severe or persistent vomiting
    5. Not waking up or not interacting
    6. Being so irritable that the child does not want to be held
    7. Flu-like symptoms improve but then return with fever and cough

    The following is the CDC's list of symptoms that should trigger emergency medical care for adults:

    1. Difficulty breathing or shortness of breath
    2. Pain or pressure in the chest or abdomen
    3. Sudden dizziness
    4. Confusion
    5. Severe or persistent vomiting
    6. Flu-like symptoms improve but then return with fever and worse cough
    7. Having a high fever for more than three days is another danger sign, according to the WHO, so the CDC has also included this as another serious symptom.

    Who should receive the flu vaccine, and who has the highest risk factors? When should someone get the flu shot?

    In the United States, the flu season usually occurs from about November until April. Officials have decided each new flu season will start each year on Oct. 4. Typically, activity is very low until December, and peak activity most often occurs between January and March. Ideally, the conventional flu vaccine should be administered between September and mid-November. It takes about one to two weeks after vaccination for antibodies against influenza to develop and provide protection. The CDC has published a summary list of their current recommendations of who should get the current vaccine:

    Summary of influenza vaccination recommendations
    • All people 6 months and older should be vaccinated annually, unless they have a rare and specific contraindication (for example, severe egg allergy, previous severe reaction to the vaccine, certain neurologic problems).
    • Protection of people at higher risk for influenza-related complications should continue to be a focus of vaccination efforts as providers and programs transition to routine vaccination of all people 6 months and older.
    • When vaccine supply is limited, vaccination efforts should focus on delivering vaccination to people who
      • are 6 months to 4 years (59 months) of age;
      • are 50 years of age and older;
      • have chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorder (including diabetes mellitus);
      • are immunosuppressed (including immunosuppression caused by medications or by human immunodeficiency virus);
      • are or will be pregnant during the influenza season;
      • are 6 months to 18 years of age and receiving long-term aspirin therapy and who therefore might be at risk for experiencing Reye's syndrome after influenza virus infection;
      • are residents of nursing homes and other chronic-care facilities;
      • are American Indians/Alaska natives;
      • are morbidly obese (body mass index is 40 or greater);
      • are health-care professionals;
      • are household contacts and caregivers of children aged younger than 5 years and adults aged 50 years and older, with particular emphasis on vaccinating contacts of children aged younger than 6 months;
      • are household contacts and caregivers of people with medical conditions that put them at higher risk for severe complications from influenza.

    As each flu season progresses and as the CDC refines its data from previous flu seasons and pandemics, this summary may be modified. The CDC publishes routine updates about the flu at Flu.gov and at http://www.cdc.gov/flu/weekly/fluactivity.htm.

    What is the prognosis (outlook) and complications for patients who get the flu?

    In general, the majority (about 90%-95%) of people who get the disease feel terrible (see symptoms) but recover with no problems. People with suppressed immune systems historically have worse outcomes than uncompromised individuals; current data suggest that pregnant individuals, children under 2 years of age, young adults, and individuals with any immune compromise or debilitation are likely to have a worse prognosis. In most outbreaks, epidemics and pandemics, the mortality rates are highest in the older population (usually above 50 years old). Complications of any flu virus infection, although relatively rare, may resemble severe viral pneumonia or the SARS (severe acute respiratory syndrome caused by a coronavirus strain) outbreak in 2002-2003 in which the disease spread to about 10 countries with over 7,000 cases, over 700 deaths, and had a 10% mortality rate.

    What is the bird (avian) flu?

    The bird flu, also known as avian influenza and H5N1, is an infection caused by avian influenza A. Bird flu can infect many bird species, including domesticated birds such as chickens. In most cases, the disease is mild; however, some subtypes can be pathogenic and rapidly kill birds within 48 hours. Rarely, humans can be infected by these bird viruses. People who get infected with bird flu usually have direct contact with the infected birds or their waste products. Depending on the viral type, the infections can range from mild influenza to severe respiratory problems or death. Human infection with bird flu is rare but frequently fatal. More than half of those people infected (over 650 infected people) have died (current estimates of the mortality [death] rates in humans is about 60%). Fortunately, this virus does not seem to be easily passed from person to person. The major concern among scientists and physicians about bird flu is that it will change (mutate) its viral RNA enough to be easily transferred among people and produce a pandemic similar to the one of 1918. There have been several isolated instances where a person had been reported to get avian flu in 2010; the virus was detected in South Korea (three human cases), resulting in a quarantine of two farms, and in 2012, over 10,000 turkeys died in a H5N1 outbreak with no human infections recorded. Recent research suggests that some people may have had exposure to H5N1 in their past but had either mild or no symptoms.

    In addition, researchers, in an effort to understand what makes an animal or bird flu become easily transmissible to humans, developed a bird flu strain that is likely easily transmitted from person to person. Although it exists only in research labs, there is controversy about both the synthesis and the scientific publication of how this potentially highly pathogenic strain was created.

    Do antiviral agents protect people from the flu?

    Vaccination is the primary method for control of influenza; however, antiviral agents have a role in the prevention and treatment of mainly influenza type A infection. Regardless, antiviral agents should not be considered as a substitute or alternative for vaccination. Most effectiveness of these drugs are reported to occur if the antivirals are given within the first 48 hours after infection; some researchers maintain there is little or no solid evidence these drugs can protect people from getting the flu so some controversies exist regarding these agents.

    The CDC published the following concerning antiviral medications:

    Antiviral medications with activity against influenza viruses are an important adjunct to influenza vaccine in the control of influenza.

    • Influenza antiviral prescription drugs can be used to treat influenza or to prevent influenza.
    • Oseltamivir and zanamivir are chemically related antiviral medications known as neuraminidase inhibitors that have activity against both influenza A and B viruses.

    Learn more about: Tamiflu | Relenza

    The following is the CDC recommended dosage for antiviral medications for the treatment of influenza (flu) for the 2014-2015 season:

    Learn more about: Symmetrel | Flumadine

    Is it safe to get a flu shot that contains thimerosal?

    Thimerosal is a preservative that contains mercury and is used in multidose vials of conventional flu vaccines to prevent contamination when the vial is repeatedly used to extract the vaccine. Although thimerosal is being phased out as a vaccine preservative, it is still used in flu vaccines in low levels. There is no data that indicates thimerosal in these vaccines has caused autism or other problems in individuals. However, flu vaccine that is produced for single use (not a multidose vial) contains no thimerosal; however, these vials are not as readily available to doctors and likely cost more to produce. Consequently, the FDA has published these two questions with clear answers that are quoted below:

    "Is it safe for children to receive an influenza vaccine that contains thimerosal?"
    "Yes. There is no convincing evidence of harm caused by the small doses of thimerosal preservative in influenza vaccines, except for minor effects like swelling and redness at the injection site."

    "Is it safe for pregnant women to receive an influenza vaccine?"
    "Yes. A study of influenza vaccination examining over 2,000 pregnant women demonstrated no adverse fetal effects associated with influenza vaccine. Case reports and limited studies indicate that pregnancy can increase the risk for serious medical complications of influenza. One study found that out of every 10,000 women in their third trimester of pregnancy during an average flu season, 25 will be hospitalized for flu-related complications."

    However, as stated above, the FDA goes on to say that single-dose vial of conventional and other flu vaccines will not contain the preservative thimerosal, so that if a person wants to avoid the thimerosal, they can ask for vaccine that comes in a single-dose vial. The nasal spray vaccine contains no thimerosal, but it is not recommended for use in pregnant women. The CDC further states, that after numerous studies, there is no established link between flu shots with or without thimerosal and autism.

    What are the causes of the flu (influenza)?

    The flu (influenza) viruses

    Influenza viruses cause the flu and are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Influenza type C differs from types A and B in some important ways. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public-health impact of influenza types A and B. Efforts to control the impact of influenza are aimed at types A and B, and the remainder of this discussion will be devoted only to these two types.

    Influenza viruses continually change over time, usually by mutation (change in the viral RNA). This constant changing often enables the virus to evade the immune system of the host (humans, birds, and other animals) so that the host is susceptible to changing influenza virus infections throughout life. This process works as follows: A host infected with influenza virus develops antibodies against that virus; as the virus changes, the "first" antibody no longer recognizes the "newer" virus and infection can occur because the host does not recognize the new flu virus as a problem until the infection is well under way. The first antibody developed may, in some instances, provide partial protection against infection with a new influenza virus. In 2009, almost all individuals had no antibodies that could recognize the novel H1N1 virus immediately.

    Type A viruses are divided into subtypes or strains based on differences in two viral surface proteins called the hemagglutinin (H) and the neuraminidase (N). There are at least 16 known H subtypes and nine known N subtypes. These surface proteins can occur in many combinations. When spread by droplets or direct contact, the virus, if not killed by the host's immune system, replicates in the respiratory tract and damages host cells. In people who are immune compromised (for example, pregnant women, infants, cancer patients, asthma patients, people with pulmonary disease and many others), the virus can cause viral pneumonia or stress the individual's system to make them more susceptible to bacterial infections, especially bacterial pneumonia. Both pneumonia types, viral and bacterial, can cause severe disease and sometimes death.

    Antigenic shift and drift

    Influenza type A viruses undergo two kinds of changes. One is a series of mutations that occurs over time and causes a gradual evolution of the virus. This is called antigenic "drift." The other kind of change is an abrupt change in the hemagglutinin and/or the neuraminidase proteins. This is called antigenic "shift." In this case, a new subtype of the virus suddenly emerges. Type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift and therefore do not cause pandemics.

    The 2009 pandemic-causing H1N1 virus is a classic example of antigenic shift. Research showed that novel H1N1 swine flu has an RNA genome that contains five RNA strands derived from various swine flu strains, two RNA strands from bird flu (also termed avian flu) strains, and only one RNA strand from human flu strains. According to the U.S. Centers for Disease Control and Prevention (CDC), mainly antigenic shifts over about 20 years led to the development of novel H1N1 flu virus. A diagram that illustrates both antigenic shift and drift can be found below (see Figure 2) and features influenza A types H1N1 and bird flu (H5N1), but almost every influenza A viral strain can go through these processes that changes the viral RNA.

    Figure 2. An example of influenza antigenic shift and drift

    What are flu (influenza) symptoms in adults and in children?

    Typical clinical features of influenza may include

    • fever (usually 100 F-103 F in adults and often even higher in children),
    • chills,
    • respiratory symptoms such as
      • cough (more often in adults),
      • sore throat (more often in adults),
      • runny or stuffy nose (especially in children),
    • headache,
    • muscle aches,
    • fatigue, sometimes extreme.

    Although nausea, vomiting, and diarrhea can sometimes accompany influenza infection, especially in children, gastrointestinal symptoms are rarely prominent. The term "stomach flu" is a misnomer that is sometimes used to describe gastrointestinal illnesses caused by other microorganisms. H1N1 infections, however, have caused more nausea, vomiting, and diarrhea than the conventional (seasonal) flu viruses.

    Most individuals who contract influenza recover in a week or two, however, others develop potentially life-threatening complications like pneumonia. In an average year, influenza is associated with about 36,000 deaths nationwide and many more hospitalizations. Flu-related complications can occur at any age; however, the elderly and people with chronic health problems are much more likely to develop serious complications after the conventional influenza infections than are younger, healthier people.

    Unfortunately, people may be contagious about 24-48 hours before symptoms appear and, for those who spontaneously recover, they may shed contagious viruses for about a week.

    How is the flu (influenza) diagnosed?

    The flu is presumptively diagnosed clinically by the patient's history of association with people known to have the disease and their symptoms listed above. Usually, a quick test (for example, nasopharyngeal swab sample) is done to see if the patient is infected with influenza A or B virus. Most of the tests can distinguish between A and B types. The test can be negative (no flu infection) or positive for types A or B. If it is positive for type A, the person could have a conventional flu strain or a potentially more aggressive strain such as H1N1. However, a new test developed by the CDC and a commercial company reportedly can detect H1N1 reliably in about one hour; the test was formerly only available to the military. In 2010, the FDA approved a commercially available test that could detect H1N1 within four hours. Most of the rapid tests are based on PCR technology that identified the genetic material of the virus.

    Swine flu (H1N1) and other influenza strains like bird flu or H3N2 are definitively diagnosed by identifying the particular antigens associated with the virus strain. In general, this testing is done in a specialized laboratory and is not done by many doctors' offices or hospital laboratories unless they have purchased the newest test systems. However, doctors' offices are able to send specimens to specialized laboratories if necessary.

    What is the key to flu (influenza) prevention?

    Flu vaccine

    Most of the illness and death caused by influenza can be prevented by annual influenza vaccination. The CDC's current Advisory Committee on Immunization Practices (ACIP) issued recommendations for everyone 6 months of age and older, who do not have any contraindications to vaccination, to receive a flu vaccine each year.

    Flu vaccine (influenza vaccine made from inactivated and sometimes attenuated [noninfective] virus or virus components) is specifically recommended for those who are at high risk for developing serious complications as a result of influenza infection.

    A new vaccine type, Fluzone Intradermal, was approved by the FDA in 2011 (for adults 18-64 years of age). This injection goes only into the intradermal area of the skin, not into the muscle (IM) like most conventional flu shots, and uses a much smaller needle than the conventional shots. This killed viral preparation is supposed to be about as effective as the IM shot but claims to produce less pain and fewer side effects (see section below).

    Are there any flu shot or nasal spray vaccine side effects in adults or in children?

    Although annual influenza (injectable) vaccination has long been recommended for people in the high-risk groups, many still do not receive the vaccine, often because of their concern about side effects. They mistakenly perceive influenza as merely a nuisance and believe that the vaccine causes unpleasant side effects or that it may even cause the flu. The truth is that influenza vaccine causes no side effects in most people. The most serious side effect that can occur after influenza vaccination is an allergic reaction in people who have a severe allergy to eggs, since the viruses used in the vaccine are grown in hens' eggs. However, a newer form of the vaccine is available that is not grown in chicken eggs. For this reason, people who have an allergy to eggs should not receive the conventional influenza vaccine, but the newer forms may be appropriate for them. Also, the vaccine is not recommended while individuals have active infections or active diseases of the nervous system. Less than one-third of those who receive the vaccine have some soreness at the vaccination site, and about 5%-10% experience mild side effects, such as headache, low-grade fever, or muscle cramps, for about a day after vaccination. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past. The intradermal shots reportedly have similar side effects as the IM shot but are less intense and may not last as long as the IM shot.

    Nevertheless, some older people remember earlier influenza vaccines that did, in fact, produce more unpleasant side effects. Vaccines produced from the 1940s to the mid-1960s were not as highly purified as modern influenza vaccines, and it was these impurities that caused most of the side effects. Since the side effects associated with these early vaccines, such as fever, headache, muscle aches, and fatigue, were similar to some of the symptoms of influenza, people believed that the vaccine had caused them to get the flu. However, injectable influenza vaccine produced in the United States has never been capable of causing influenza because it consists of killed virus.

    Another type of influenza vaccine (nasal spray) is made with live attenuated (altered) influenza viruses. This vaccine is made with live viruses that can stimulate the immune response enough to confer immunity but do not cause classic influenza symptoms (in most instances). The nasal spray vaccine (Flumist) is only approved for healthy individuals ages 2-49 years of age and is recommended preferentially for healthy children aged 2 through 8 who do not have contraindications to receiving the vaccine, if it is readily available. This nasal spray vaccine contains live attenuated virus (less able to cause flu symptoms due to a designed inability to replicate at normal body temperatures). This live vaccine could possibly cause the disease in infants and immunocompromised people and does not produce a strong immune response in many older people. Side effects of the nasal spray vaccine include nasal congestion, sore throat, and fever. Headaches, muscle aches, irritability, and malaise have also been noted. In most instances, if side effects occur, they only last a day or two. This nasal spray has been produced for conventional flu viruses and should not be given to pregnant women or anyone who has a medical condition that may compromise the immune system because in some instances the flu may be a side effect.

    Some people do not receive influenza vaccine because they believe it is not very effective. There are several different reasons for this belief. People who have received influenza vaccine may subsequently have an illness that is mistaken for influenza, and they believe that the vaccine failed to protect them. In other cases, people who have received the vaccine may indeed have an influenza infection. Overall vaccine effectiveness varies from year to year, depending upon the degree of similarity between the influenza virus strains included in the vaccine and the strain or strains that circulate during the influenza season. Because the vaccine strains must be chosen nine to 10 months before the influenza season, and because influenza viruses mutate over time, sometimes mutations occur in the circulating virus strains between the time the vaccine strains are chosen and the next influenza season ends. These mutations sometimes reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby reducing vaccine efficacy. This commonly occurs with the conventional flu vaccines as the specific virus types chosen for vaccine inclusion are based on reasoned projections for the upcoming flu season. Occasionally, the vaccine does not match the actual predominating virus strain and is not very effective in generating a specific immune response to the predominant infecting flu strain.

    Vaccine efficacy also varies from one person to another. Studies of healthy young adults have shown influenza vaccine to be 70%-90% effective in preventing illness. In the elderly and those with certain chronic medical conditions such as HIV, the vaccine is often less effective in preventing illness. Studies show the vaccine reduces hospitalization by about 70% and death by about 85% among the elderly who are not in nursing homes. Among nursing-home residents, vaccine can reduce the risk of hospitalization by about 50%, the risk of pneumonia by about 60%, and the risk of death by 75%-80%. If antigenic drift results in changing the circulating virus from the strains used in the vaccine, vaccine efficacy may be reduced. However, the vaccine is still likely to lessen the severity of the illness and to prevent complications and death.

    Recent studies suggest that in younger children (ages 2-8) the nasal spray flu vaccine may prevent about 50% more cases of flu than the vaccine administered by the flu shot. Therefore, children in this age group who have no contraindications should receive this form of the vaccine if it is available. However, the CDC recommends that vaccination not be delayed if this form is not available; the flu shot should be given in this case.

    Why should the flu (influenza) vaccine be taken every year?

    Although only a few different influenza virus strains circulate at any given time, people may continue to become ill with the flu throughout their lives. The reason for this continuing susceptibility is that influenza viruses are continually mutating, through the mechanisms of antigenic shift and drift described above. Each year, the vaccine is updated to include the most current influenza virus strains that are infecting people worldwide. The fact that influenza viral genes continually change is one of the reasons vaccine must be taken every year. Another reason is that antibody produced by the host in response to the vaccine declines over time, and antibody levels are often low one year after vaccination so even if the same vaccine is used, it can act as a booster shot to raise immunity.

    Because of the vaccine synthesis and distribution problems with the pandemic H1N1 vaccines, a number of companies have begun development of new vaccine synthesis technologies to avoid the variable production quantities of virus and the long growth cycle and purification process in chicken eggs. There are at least five new technologically novel approaches under development (recombinant protein, virus-like particle synthesis, viral vectors, DNA-based vaccines [altered plasmids] and viral vectors that contain specific antigens). The CDC has indicated they plan to overhaul their vaccine distribution system, especially for those instances when a pandemic strain arises. Several vaccines have undergone clinical trials and have been approved for use.

    Many people still refuse to get flu shots because of misunderstandings, fear, "because I never get any shots," or simply a belief that if they get the flu, they will do well. These are only some of the reasons -- there are many more. The U.S. and other countries populations need to be better educated about vaccines; at least they should realize that safe vaccines have been around for many years (measles, mumps, chickenpox, and even a vaccine for cholera), and as adults they often have to get a vaccine-like shot to test for tuberculosis exposure or to protect themselves from tetanus. The flu vaccines are as safe as these vaccines and shots that are widely accepted by the public. Consequently, better efforts need to be made to make yearly flu vaccines as widely acceptable as other vaccines. Susceptible people need to understand that the vaccines afford them a significant chance to reduce or prevent this potentially debilitating disease, hospitalization and, in a few, a lethal flu-caused disease.

    What are some flu treatments an individual can do at home?

    First, individuals should be sure they are not members of a high-risk group that is more susceptible to getting severe flu symptoms. Check with your physician if you are unsure if you are a higher-risk person. Home care is recommended by the CDC if a person is normally healthy with no underlying diseases or conditions (for example, asthma, lung disease, pregnant, or immunosuppressed).

    Increasing liquid intake, warm showers, and warm compresses, especially in the nasal area, can reduce the body aches and reduce nasal congestion. Nasal strips and humidifiers may help reduce congestion, especially while trying to sleep. Some physicians recommend nasal irrigation with saline to further reduce congestion; some recommend nonprescription decongestants. Fever can be treated with over-the-counter acetaminophen (Tylenol) or ibuprofen (Motrin and others); read labels for safe dosage. Cough can be suppressed by cough drops and over-the-counter cough syrup. If an individual's symptoms at home get worse, their doctor should be notified.

    Learn more about: Tylenol

    When should a person go to the emergency department for the flu?

    The CDC urges people to seek emergency medical care for a sick child with any of these symptoms:

    1. Fast breathing or trouble breathing
    2. Bluish or gray skin color
    3. Not drinking enough fluids
    4. Severe or persistent vomiting
    5. Not waking up or not interacting
    6. Being so irritable that the child does not want to be held
    7. Flu-like symptoms improve but then return with fever and cough

    The following is the CDC's list of symptoms that should trigger emergency medical care for adults:

    1. Difficulty breathing or shortness of breath
    2. Pain or pressure in the chest or abdomen
    3. Sudden dizziness
    4. Confusion
    5. Severe or persistent vomiting
    6. Flu-like symptoms improve but then return with fever and worse cough
    7. Having a high fever for more than three days is another danger sign, according to the WHO, so the CDC has also included this as another serious symptom.

    Who should receive the flu vaccine, and who has the highest risk factors? When should someone get the flu shot?

    In the United States, the flu season usually occurs from about November until April. Officials have decided each new flu season will start each year on Oct. 4. Typically, activity is very low until December, and peak activity most often occurs between January and March. Ideally, the conventional flu vaccine should be administered between September and mid-November. It takes about one to two weeks after vaccination for antibodies against influenza to develop and provide protection. The CDC has published a summary list of their current recommendations of who should get the current vaccine:

    Summary of influenza vaccination recommendations
    • All people 6 months and older should be vaccinated annually, unless they have a rare and specific contraindication (for example, severe egg allergy, previous severe reaction to the vaccine, certain neurologic problems).
    • Protection of people at higher risk for influenza-related complications should continue to be a focus of vaccination efforts as providers and programs transition to routine vaccination of all people 6 months and older.
    • When vaccine supply is limited, vaccination efforts should focus on delivering vaccination to people who
      • are 6 months to 4 years (59 months) of age;
      • are 50 years of age and older;
      • have chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorder (including diabetes mellitus);
      • are immunosuppressed (including immunosuppression caused by medications or by human immunodeficiency virus);
      • are or will be pregnant during the influenza season;
      • are 6 months to 18 years of age and receiving long-term aspirin therapy and who therefore might be at risk for experiencing Reye's syndrome after influenza virus infection;
      • are residents of nursing homes and other chronic-care facilities;
      • are American Indians/Alaska natives;
      • are morbidly obese (body mass index is 40 or greater);
      • are health-care professionals;
      • are household contacts and caregivers of children aged younger than 5 years and adults aged 50 years and older, with particular emphasis on vaccinating contacts of children aged younger than 6 months;
      • are household contacts and caregivers of people with medical conditions that put them at higher risk for severe complications from influenza.

    As each flu season progresses and as the CDC refines its data from previous flu seasons and pandemics, this summary may be modified. The CDC publishes routine updates about the flu at Flu.gov and at http://www.cdc.gov/flu/weekly/fluactivity.htm.

    What is the prognosis (outlook) and complications for patients who get the flu?

    In general, the majority (about 90%-95%) of people who get the disease feel terrible (see symptoms) but recover with no problems. People with suppressed immune systems historically have worse outcomes than uncompromised individuals; current data suggest that pregnant individuals, children under 2 years of age, young adults, and individuals with any immune compromise or debilitation are likely to have a worse prognosis. In most outbreaks, epidemics and pandemics, the mortality rates are highest in the older population (usually above 50 years old). Complications of any flu virus infection, although relatively rare, may resemble severe viral pneumonia or the SARS (severe acute respiratory syndrome caused by a coronavirus strain) outbreak in 2002-2003 in which the disease spread to about 10 countries with over 7,000 cases, over 700 deaths, and had a 10% mortality rate.

    What is the bird (avian) flu?

    The bird flu, also known as avian influenza and H5N1, is an infection caused by avian influenza A. Bird flu can infect many bird species, including domesticated birds such as chickens. In most cases, the disease is mild; however, some subtypes can be pathogenic and rapidly kill birds within 48 hours. Rarely, humans can be infected by these bird viruses. People who get infected with bird flu usually have direct contact with the infected birds or their waste products. Depending on the viral type, the infections can range from mild influenza to severe respiratory problems or death. Human infection with bird flu is rare but frequently fatal. More than half of those people infected (over 650 infected people) have died (current estimates of the mortality [death] rates in humans is about 60%). Fortunately, this virus does not seem to be easily passed from person to person. The major concern among scientists and physicians about bird flu is that it will change (mutate) its viral RNA enough to be easily transferred among people and produce a pandemic similar to the one of 1918. There have been several isolated instances where a person had been reported to get avian flu in 2010; the virus was detected in South Korea (three human cases), resulting in a quarantine of two farms, and in 2012, over 10,000 turkeys died in a H5N1 outbreak with no human infections recorded. Recent research suggests that some people may have had exposure to H5N1 in their past but had either mild or no symptoms.

    In addition, researchers, in an effort to understand what makes an animal or bird flu become easily transmissible to humans, developed a bird flu strain that is likely easily transmitted from person to person. Although it exists only in research labs, there is controversy about both the synthesis and the scientific publication of how this potentially highly pathogenic strain was created.

    Do antiviral agents protect people from the flu?

    Vaccination is the primary method for control of influenza; however, antiviral agents have a role in the prevention and treatment of mainly influenza type A infection. Regardless, antiviral agents should not be considered as a substitute or alternative for vaccination. Most effectiveness of these drugs are reported to occur if the antivirals are given within the first 48 hours after infection; some researchers maintain there is little or no solid evidence these drugs can protect people from getting the flu so some controversies exist regarding these agents.

    The CDC published the following concerning antiviral medications:

    Antiviral medications with activity against influenza viruses are an important adjunct to influenza vaccine in the control of influenza.

    • Influenza antiviral prescription drugs can be used to treat influenza or to prevent influenza.
    • Oseltamivir and zanamivir are chemically related antiviral medications known as neuraminidase inhibitors that have activity against both influenza A and B viruses.

    Learn more about: Tamiflu | Relenza

    The following is the CDC recommended dosage for antiviral medications for the treatment of influenza (flu) for the 2014-2015 season:

    Learn more about: Symmetrel | Flumadine

    Is it safe to get a flu shot that contains thimerosal?

    Thimerosal is a preservative that contains mercury and is used in multidose vials of conventional flu vaccines to prevent contamination when the vial is repeatedly used to extract the vaccine. Although thimerosal is being phased out as a vaccine preservative, it is still used in flu vaccines in low levels. There is no data that indicates thimerosal in these vaccines has caused autism or other problems in individuals. However, flu vaccine that is produced for single use (not a multidose vial) contains no thimerosal; however, these vials are not as readily available to doctors and likely cost more to produce. Consequently, the FDA has published these two questions with clear answers that are quoted below:

    "Is it safe for children to receive an influenza vaccine that contains thimerosal?"
    "Yes. There is no convincing evidence of harm caused by the small doses of thimerosal preservative in influenza vaccines, except for minor effects like swelling and redness at the injection site."

    "Is it safe for pregnant women to receive an influenza vaccine?"
    "Yes. A study of influenza vaccination examining over 2,000 pregnant women demonstrated no adverse fetal effects associated with influenza vaccine. Case reports and limited studies indicate that pregnancy can increase the risk for serious medical complications of influenza. One study found that out of every 10,000 women in their third trimester of pregnancy during an average flu season, 25 will be hospitalized for flu-related complications."

    However, as stated above, the FDA goes on to say that single-dose vial of conventional and other flu vaccines will not contain the preservative thimerosal, so that if a person wants to avoid the thimerosal, they can ask for vaccine that comes in a single-dose vial. The nasal spray vaccine contains no thimerosal, but it is not recommended for use in pregnant women. The CDC further states, that after numerous studies, there is no established link between flu shots with or without thimerosal and autism.

    Source: http://www.rxlist.com

    First, individuals should be sure they are not members of a high-risk group that is more susceptible to getting severe flu symptoms. Check with your physician if you are unsure if you are a higher-risk person. Home care is recommended by the CDC if a person is normally healthy with no underlying diseases or conditions (for example, asthma, lung disease, pregnant, or immunosuppressed).

    Increasing liquid intake, warm showers, and warm compresses, especially in the nasal area, can reduce the body aches and reduce nasal congestion. Nasal strips and humidifiers may help reduce congestion, especially while trying to sleep. Some physicians recommend nasal irrigation with saline to further reduce congestion; some recommend nonprescription decongestants. Fever can be treated with over-the-counter acetaminophen (Tylenol) or ibuprofen (Motrin and others); read labels for safe dosage. Cough can be suppressed by cough drops and over-the-counter cough syrup. If an individual's symptoms at home get worse, their doctor should be notified.

    Learn more about: Tylenol

    Source: http://www.rxlist.com

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