People who received flu shots were protected from the illness for up to six months post-vaccination, which is the duration of most flu seasons, according to a study presented at the 2015 International Conference on Emerging Infectious Diseases.
Researchers at the Naval Health Research Center in San Diego assessed flu vaccine protection declines using data from 1,720 Department of Defense non-active duty beneficiaries who sought care at three clinics for fever, cough or sore throat throughout four flu seasons. Swabs were taken from the patients and were tested for the flu.
The study results showed that giving flu vaccines in the fall can prevent the greatest number of infections. While researchers found people had moderate protection for up to six months after getting the flu shot, they saw a marked decline in protection after the six-month mark, meaning yearly vaccination would be best.