The flu vaccine typically takes about 2 weeks after vaccination to become effective. Its protection generally lasts throughout the current flu season, which is usually around 6 months. However, the effectiveness can gradually decrease over time, starting around 41 days after vaccination, with protection waning approximately 9% every 28 days in adults. Because flu viruses constantly change each season, and immunity wanes, it is recommended to get a flu vaccine annually to maintain optimal protection. Protection duration depends on factors such as age, health, and how well the vaccine matches circulating flu strains. Special high-dose vaccines are available for people 65 and older to provide stronger protection, as immunity tends to decrease faster in this age group. Even though the vaccine may not fully prevent flu, it helps reduce the severity and duration of illness if one contracts the virus after vaccination.
