Do you need to get a flu vaccination again in 90 days?

Otherwise healthy adults, teens and children over 10 only need a single vaccination for the flu to be fully protected. After about 2 weeks from the time of the vaccination you will be protected. Younger children need a series of two flu vaccinations, usually given a month apart. After around another 2 weeks from the time of the second vaccination, they are protected. Babies under 6 months old do not have immune systems mature enough to get vaccinated for the flu.