Key Facts about Seasonal Flu Vaccine from the Centers for Disease Control and Prevention Why should people get vaccinated against the flu? Influenza is a serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and influenza infection can affect people differently. Even healthy people can get very sick from the flu and spread it to others. Over a period of 31 seasons between 1976 and 2007, estimates of flu-associated deaths in the United States range from a low of about 3,000 to a high of about 49,000 people. During a regular flu season, about 90 percent of deaths occur in people 65 years and older. The seasonal flu season in the United States can begin as early as October and last as late as May. During this time, flu viruses are circulating in the population. An annual seasonal flu vaccine (either the flu shot or the nasal-spray flu vaccine) is the best way to reduce the chances that you will get seasonal flu and lessen the chance that you will spread it to others. When more people get vaccinated against the flu, less flu can spread through that community. How do flu vaccines work? Flu vaccines (the flu shot and the nasal-spray flu vaccine (LAIV)) cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine. The seasonal flu vaccine protects against three influenza viruses that research indicates will be most common during the upcoming season. Three kinds of influenza viruses commonly circulate among people today: influenza B viruses, influenza A (H1N1) viruses, and influenza A (H3N2) viruses. Each year, one flu virus of each kind is used to produce seasonal influenza vaccine. What kinds of flu vaccines are available? There are two types of vaccines: The flu shot an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. The flu shot is approved for use in people older than 6 months, including healthy people and people with chronic medical conditions. There are three different flu shots available: o a regular flu shot approved for people ages 6 months and older o a high-dose flu shot approved for people 65 and older, and
o an intradermal flu shot approved for people 18 to 64 years of age. The nasal-spray flu vaccine a vaccine made with live, weakened flu viruses that is given as a nasal spray (sometimes called LAIV for Live Attenuated Influenza Vaccine ). The viruses in the nasal spray vaccine do not cause the flu. LAIV is approved for use in healthy* people 2 through 49 years of age who are not pregnant. Seasonal flu vaccines protect against the three influenza viruses (trivalent) that research indicates will be most common during the upcoming season. The viruses in the vaccine can change each year based on international surveillance and scientists estimations about which types and strains of viruses will circulate in a given year. While some manufacturers are planning to produce a quadrivalent (four component) vaccine in the future, quadrivalent vaccines are not expected to be available for the 2012-2013 season. About 2 weeks after vaccination, antibodies that provide protection against the influenza viruses in the vaccine develop in the body. Information specific to the 2012-2013 season including the flu vaccine formulation, can be found at 2012-2013 Flu Season. Who Should Get Vaccinated This Season? Everyone who is at least 6 months of age should get a flu vaccine this season. It s especially important for some people to get vaccinated. Those people include the following: People who are at high risk of developing serious complications like pneumonia if they get sick with the flu. This includes: o People who have certain medical conditions including asthma, diabetes, and chronic lung disease. o Pregnant women. o People 65 years and older People who live with or care for others who are high risk of developing serious complications. This includes: o household contacts and caregivers of people with certain medical conditions including asthma, diabetes, and chronic lung disease. A detailed list is available at Who Should Get Vaccinated Against Influenza. A complete list of health and age factors that are known to increase a person s risk of developing serious complications from flu is available at People Who Are at High Risk of Developing Flu-Related Complications.
Who Should Not Be Vaccinated? There are some people who should not get a flu vaccine without first consulting a physician. These include: People who have a severe allergy to chicken eggs. People who have had a severe reaction to an influenza vaccination. Children younger than 6 months of age (influenza vaccine is not approved for this age group), and People who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated.) People with a history of Guillain Barré Syndrome (a severe paralytic illness, also called GBS) that occurred after receiving influenza vaccine and who are not at risk for severe illness from influenza should generally not receive vaccine. Tell your doctor if you ever had Guillain-Barré Syndrome. Your doctor will help you decide whether the vaccine is recommended for you. When Should I Get Vaccinated? CDC recommends that people get vaccinated against influenza as soon as flu season vaccine becomes available in their community. Influenza seasons are unpredictable, and can begin as early as October. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against the flu. Flu vaccine is produced by private manufacturers, so availability depends on when production is completed. If everything goes as indicated by manufacturers, shipments are likely to begin in August and continue throughout September and October until all vaccine is distributed. Doctors and nurses are encouraged to begin vaccinating their patients as soon as flu vaccine is available in their areas, even as early as August. Where can I get a flu vaccine? Flu vaccines are offered in many locations, including doctor s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools. Even if you don t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work. The following Flu Near You: Vaccine Locator is a useful tool for finding vaccine in your area.
Why Do I Need a Flu Vaccine Every Year? A flu vaccine is needed every year because flu viruses are constantly changing. It s not unusual for new flu viruses to appear each year. The flu vaccine is formulated each year to keep up with the flu viruses as they change. Also, multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time. Getting vaccinated each year provides the best protection against influenza throughout flu season. Does flu vaccine work right away? No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. In the meantime, you are still at risk for getting the flu. That s why it s better to get vaccinated early in the fall, before the flu season really gets under way. Can I get seasonal flu even though I got a flu vaccine this year? Yes. The ability of flu vaccine to protect a person depends on two things: 1) the age and health status of the person getting vaccinated, and 2) the similarity or match between the virus strains in the vaccine and those circulating in the community. If the viruses in the vaccine and the influenza viruses circulating in the community are closely matched, vaccine effectiveness is higher. If they are not closely matched, vaccine effectiveness can be reduced. However, it s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different, but related strains of influenza viruses. Vaccine Effectiveness Influenza vaccine effectiveness (VE) can vary from year to year and among different age and risk groups. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work? Will This Season's Vaccine Be a Good Match for Circulating Viruses? It's not possible to predict with certainty which flu viruses will predominate during a given season. Flu viruses are constantly changing (called antigenic drift ) they can change from one season to the next or they can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in
advance in order for vaccine to be produced and delivered on time. Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses in the vaccine. How Do We Know if There is a Good Match Between the Vaccine Viruses and Those Causing Illness? Over the course of a flu season, CDC studies samples of flu viruses circulating during that season to evaluate how close a match there is between viruses used to make the vaccine and circulating viruses. Data are published in the weekly FluView. In addition, CDC conducts studies each year to determine how well the vaccine protects against illness. Can the Vaccine Provide Protection Even if the Vaccine is Not a "Good" Match? Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related viruses. A less than ideal match may result in reduced vaccine effectiveness against the virus that is different from what is in the vaccine, but it can still provide some protection against influenza illness. In addition, it's important to remember that the flu vaccine contains three virus viruses so that even when there is a less than ideal match or lower effectiveness against one virus, the vaccine may protect against the other viruses. For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend flu vaccination. This is particularly important for people at high risk for serious flu complications, and their close contacts. In What Years Was There a Good Match Between the Vaccine and the Circulating Viruses? In recent years the match between the vaccine viruses and those identified during the flu season has usually been good. In 18 of the last 22 U.S. influenza seasons the viruses in the influenza vaccine have been well matched to the predominant circulating viruses. Since 1990, there has only been one season (1997-98) when there was very low crossreaction between the viruses in the seasonal vaccine and the predominant circulating virus, and three seasons (1992-93, 2003-04, and 2007-08) when there was low crossreaction.
Vaccine Side Effects (What to Expect) Different side effects can be associated with the flu shot and LAIV. The flu shot: The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. Some minor side effects that could occur are: Soreness, redness, or swelling where the shot was given Fever (low grade) Aches If these problems occur, they begin soon after the shot and usually last 1 to 2 days. Almost all people who receive influenza vaccine have no serious problems from it. However, on rare occasions, flu vaccination can cause serious problems, such as severe allergic reactions. As of July 1, 2005, people who think that they have been injured by the flu shot can file a claim for compensation from the National Vaccine Injury Compensation Program (VICP). The nasal spray (also called LAIV or FluMist ): The viruses in the nasal-spray vaccine are weakened and do not cause severe symptoms often associated with influenza illness. (In clinical studies, transmission of vaccine viruses to close contacts has occurred only rarely.) In children, side effects from LAIV (FluMist ) can include: runny nose wheezing headache vomiting muscle aches fever In adults, side effects from LAIV (FluMist ) can include runny nose headache sore throat cough More information about the safety of flu vaccines is available at Influenza Vaccine Safety.