Many people are not aware of the seriousness of influenza infection and some believe that the vaccine can cause the flu. Influenza vaccine produced in the United States cannot cause influenza. The only type of influenza vaccine that has been licensed in the United States is made from killed influenza viruses, which cannot cause infection. An influenza vaccine that is made with live influenza viruses has been developed and may be marketed in the future. This vaccine is made with viruses that can confer immunity but do not cause classic influenza symptoms.
Some people worry about the side effects of influenza vaccine.
While influenza vaccine, like any other vaccine or medicine, is capable of causing serious problems such as severe allergic reactions, the risk of the vaccine causing serious harm, or death, is extremely small. Almost all people who get influenza vaccine have no serious problems from it. The most common side effect from influenza vaccination is soreness at the site of the injection. The soreness can last up to 2 days but is usually mild and does not affect a person's ability to perform their normal daily activities. Some people, usually children who have not been exposed to influenza virus in the past, may have fever and body aches after vaccination.