With the availability of two types of vaccines,decisions about which one to use will be based on a variety of factors, including cost, route of administration,and side effects.9,10,17 Differential vaccine efficacy will also be a major consideration in the choice of vaccine. Unlike the situation in children — particularly, but not limited
to, those younger than 6 years of age, for whom the live attenuated vaccine appears to be superior to the inactivated vaccine18 — the relative and even absolute efficacies of the live attenuated vaccine in adults have not previously been
well established.3,5