/Why are so many doses needed for each vaccine?

Getting every recommended dose of each vaccine provides your child with the best protection possible.

Depending on the vaccine, more than one dose is needed to build high enough immunity to prevent disease, boost immunity that fades over time, make sure people who did not get immunity from a first dose are protected, or protect against germs that change over time, like flu.

Every dose of a vaccine is important because they all protect against infectious diseases that are threats today and can be especially serious for infants and very young children.