Influenza Virus Vaccine Influenza, also known as the flu, is a contagious disease that is caused by influenza viruses. Influenza viruses infect the respiratory tract (nose, throat, and lungs) in humans. The flu is different from a cold, mainly because the symptoms and complications are more severe. Influenza usually comes on suddenly and may include these symptoms: fever, headache, malaise (a feeling of being ill and without energy that can be extreme), cough, sore throat, nasal congestion and body aches. A lot of the illness and death caused by the flu can be prevented by a yearly flu vaccine. People in high-risk groups and people who are in close contact with those at high risk should get a flu vaccine every year as recommended by the Advisory Committee on Immunization Practices (ACIP) . A flu vaccine can be given to anyone who wants to avoid the flu (persons over 6 months of age). Persons who provide important community services (such as police, fire department personnel, emergency medical services) should consider getting a flu vaccine so that those services are not disrupted during a flu outbreak. Seasonal Information -     2004-2005     2003-2004     2002-2003     2001-2002     2000-2001   Influenza Prevention and Control (CDC) Draft Pandemic Influenza Preparedness and Response Plan Workshop on Development of Clinical Trial Plan for Pandemic Influenza Vaccines Questions and Answers on FluMist (Influenza Virus Vaccine Live, Intranasal) Can inactivated influenza virus vaccine be used after its expiration date? FDA does not recommend the use of any vaccine beyond the labeled expiration date. The primary purpose of the expiration date is to ensure that vaccines used in clinical practice meet their release specifications, which ensures that they continue to be safe and efficacious. Release specifications include potency (strength), content of excipients, and sterility. The maintenance of vaccine release specifications over time (stability of the product) is monitored by each manufacturer for representative lots of influenza vaccine under controlled, documented storage conditions. The expiration date of a vaccine is based on these studies. Although vaccine under proper storage conditions may maintain release specifications beyond the expiration date, the potency of inactivated influenza vaccines is generally declining gradually from the time of manufacture, and the rates of decline may vary. Variation in the rate of decline is partly related to differences in the specific strains used from year to year for vaccine production. An increased rate of decline occurs when the vaccine is exposed to temperatures outside the range recommended for optimal storage (generally 2-8°C). To ensure maximal safety and efficacy of inactivated influenza virus vaccines, particularly for patients at risk of complications from influenza virus infection, FDA strongly recommends the use of only vaccine that is not past its expiration date. Vaccine for the upcoming flu season is available in the late summer to early fall in most years. If the composition of inactivated influenza virus vaccine remains the same, is it necessary to be re-immunized? ACIP recommends annual re-immunization. Antibodies to hemagglutinins, a part of the virus, are the most important feature of protection against influenza virus infection. After immunization with inactivated influenza virus vaccine (two doses for young children and one dose for older children and adults), hemagglutination inhibition antibody titers in the blood reach a peak within 2-3 weeks, but decline over the next several months back toward the baseline.   Updated August 27, 2004   CBER Home Page | CBER A-Z Index | CBER Search | Contact CBER FDA Home Page | Search FDA Site | FDA A-Z Index | Contact FDA | Privacy | Accessibility | HHS Home Page FDA / Center for Biologics Evaluation and Research