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Flu Vaccine (cont.)

Side Effects or Reactions to Flu Vaccines and Flu Vaccine Safety (Seasonal and Pandemic)

In general, all medications, including intramuscular, intradermal, and nasal-spray vaccines, have side effects and the potential for allergic reactions. For most medicines and vaccines, the side effects or reactions are infrequent and are minimal if they do occur. The seasonal and pandemic vaccines (including nasal sprays and intradermal vaccine) are no different. What is different about the side effects of flu vaccines is that the occasional side effects seen with all flu vaccines usually resemble the flu disease; about 5%-10% of people experience mild side effects, such as headache, nasal congestion, low-grade fever, sore throat, or muscle cramps, for about a day after vaccination. Although these are short-lived, some people think they contracted the flu from the vaccine. This is a myth. The intramuscular and intradermal vaccines contain no live virus, so the vaccine cannot transmit the disease. Although the nasal-spray vaccines contain live virus, it contains weakened (attenuated) virus. The vast majority of viruses that are attenuated (altered so they will not replicate or do so poorly) will not be able to cause influenza in people with normal immune systems and good health because the attenuated viruses replicate poorly or not at all in these people. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past, but they can occur in some adults. About one-third or fewer of those vaccinated develop soreness and occasional redness at the injection site. Allergic reactions are rare; however, people allergic to eggs should not get the intramuscular or nasal-spray vaccine. Intramuscular vaccine shots are usually mildly painful when injected into muscle tissue, the new intradermal shots use a very small needle and require 40% less viral antigen, and most people find them to be far less painful than the intramuscular shots.

The CDC published safety data on the H1N1 vaccine. They concluded the vaccine showed a good safety profile. These studies are ongoing since H1N1 strains were part of the trivalent seasonal vaccine for the two years following the outbreak. Currently, the CDC concludes that the seasonal trivalent vaccines are safe, but they are still monitoring the vaccines for any problems, as with all vaccines. In addition, the new quadrivalent vaccines have undergone similar safety tests; this flu season, the new vaccines will also be retrospectively examined for any changes in effectiveness as compared to previous trivalent vaccines.

Medically Reviewed by a Doctor on 9/2/2014

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