Other persons who wish to reduce the likelihood of becoming ill with the flu. In the United States, the flu usually occurs from about November until April. The number of flu cases is normally low until December, and peak flu activity is seen between late December and early March. Adults and older children are vaccinated in the upper arm muscle and young children in the thigh muscle. The benefits of the flu vaccine last less than one year, so it is necessary to be revaccinated each year.
Most people report no side effects from the flu vaccine.
The most serious side effect that can occur in people receiving the vaccine is an allergic reaction in those who have a serious allergy to eggs, since the viruses used in the vaccine are grown in hens' eggs. For this reason, people who have an allergy to eggs should not get the flu vaccine. Some people do not receive the flu vaccine because they erroneously believe that the vaccine may cause the flu. This is not possible, since the vaccine is manufactured from killed influenza viruses, which are not capable of causing infection. References American Academy of Family Physicians Centers for Disease Control and Prevention.