Which of the following vaccines is typically recommended for adults on a booster schedule?

The influenza vaccine is typically recommended for adults on an annual booster schedule. Unlike some vaccines that provide long-term protection after a series of doses, the effectiveness of the influenza vaccine can wane over time due to changes in the virus and the need to update the vaccine to match circulating strains. Therefore, an annual vaccination is recommended to maintain immunity and provide the best protection against seasonal influenza.

In contrast, the MMR vaccine, which protects against measles, mumps, and rubella, is usually administered in childhood with a specific schedule of two doses. Adults who have received the complete series in childhood do not typically require booster doses unless they are at higher risk or during outbreaks. The polio vaccine is generally given during childhood with several doses, and boosters are rarely needed in adults except for specific situations like travel to certain regions or specific occupational exposures. The hepatitis B vaccine also comprises a series of doses, typically given in childhood or adulthood for those at risk, but routine booster doses are not commonly recommended for most adults.