Introduction Each year, as flu season approaches, health experts recommend getting a flu vaccine. Yet many wonder: why does the flu vaccine change every year? Why can’t one shot protect us for life like vaccines for other diseases? The answer lies in the complex, ever-evolving nature of the influenza virus. This article dives into the science behind flu strains, how the virus changes, and why vaccine formulations must adapt annually to provide effective protection. Understanding the Influenza Virus Influenza viruses belong to the Orthomyxoviridae family and primarily infect the respiratory tract. There are four types of influenza viruses: The two…