Health Library

What Are Booster Shots?

A booster shot is a dose of vaccine given after a person has had the original vaccine (sometimes called a primary dose or, if more than one dose, primary series). Immunity from the original vaccine can fade over time, and a booster shot can help the immune system “boost” the protection it provides.

Boosters aren’t new. They are given for many vaccines that kids and adults get. For example, kids get vaccines around the time they start school to boost the vaccines they got as infants and toddlers. Pregnant women get a Tdap booster to protect their newborn from pertussis. And anyone over 6 months old should get a flu shot each year, which is also a type of booster.

Why Do People Need a COVID-19 Booster Shot?

Safe and effective COVID-19 vaccines are recommended for all adults and children ages 6 months and up. They are very good at preventing serious illness, hospitalization, and death due to COVID-19.

As with other vaccines, the immune protection from the COVID-19 vaccine can fade over time. Booster shots are recommended for everyone age 6 months and older. The type of booster shot used and when it’s given after the primary series may differ depending on a child’s age and health status. As time goes on, people might need additional booster shots. Talk to your doctor if you have questions about the different types of booster shots and when your child might be eligible for one.

Is a COVID-19 Booster Shot the Same as an “Additional Dose”?

No. An additional dose is an extra dose of vaccine given as part of the primary series when a person is first vaccinated. Some people with weak immune systems might get a poor response from the primary series of the COVID-19 vaccine. This can include people who are being treated for cancer, have had an organ transplant, or take medicines that weaken the immune system. This added dose helps their immune system reach the same level of protection as in people with stronger immune systems.

Kids ages 6 months through 4 years with a weak immune system may need an additional dose. This depends on which vaccine they get:

• Kids who get the Pfizer-BioNtech vaccine get 3 doses in their primary series. This is true for both healthy kids as well as those with weak immune systems. No additional doses are needed for this group.
• Kids who get the Moderna vaccine get 2 doses in their primary series. Kids with weak immune systems get an additional dose at least 4 weeks later.

Kids ages 5 and older get 2 doses in their primary series. Those with weak immune systems get an additional dose at least 4 weeks later.

Kids who get additional doses in their primary series will still need booster shots as time passes, just like everyone else.

What Does It Mean for My Family?

Being up to date on COVID-19 vaccination might mean a different number of doses for kids in different health situations. But it’s an important way to protect kids and adults from getting very sick. Talk to your doctor if you aren’t sure if your child needs an additional dose after their primary COVID-19 vaccine series, or to see when your child might need a booster shot.

The CDC has more information about COVID-19 vaccines and booster shots.