Why are so many doses needed for each vaccine?

One dose of a vaccine is not enough to protect a child against some diseases. Depending on the vaccine and the disease, more than one dose is needed to build high enough immunity to prevent the 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, such as flu. This is because what’s in most childhood vaccines is inactive (i.e. dead) viruses or bacteria, which is why vaccines can’t get you sick. But because the viruses or bacteria are inactive, the immune system needs to respond to it multiple times for full protection. Scientists and medical providers study the best combination of timing and number of doses needed for full protection against diseases.

Learn more about this concept, known as waning immunity.

Source: CDC: The Childhood Immunization Schedule


You’ve got questions. That’s a good thing.

As parents, determining how best to protect our children can be overwhelming and confusing. We’re here to help.

Related Questions

The vaccine’s safety was studied in approximately 3,100 children ages 5 through 11 who received the vaccine and no serious side effects have been detected in the ongoing study…
Minors, 5 through 17 years of age, need parental consent to be vaccinated…


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About I Vaccinate

I Vaccinate provides information and tools based on real medical science and research to help Michigan parents protect their kids. Support is provided by the Michigan Department of Health and Human Services and the Franny Strong Foundation.

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