What are vaccines and how do they work? Why do some vaccines seem to be more successful than others? For example, vaccines such as the MMR, HPV, and polio vaccines typically lead to lifelong immunity after an initial dose and 2-3 boosters. On the other hand, vaccinations for influenza and tetanus must be given every year or every few years, respectively. How does the host’s immune system and its responses to different types of antigens impact the efficacy of certain vaccines? How do the genetics of certain organisms (such as influenza) influence vaccine efficacy?
