What Are Booster Shots?

Medically Reviewed by Sabrina Felson, MD on March 05, 2024
Written by Shishira Sreenivas
3 min read

Vaccines help protect us from dangerous viruses and bacteria. Once you've had a shot for a particular disease, you might think you're always safe from it. But that's not necessarily the case.

For some diseases, you need more than one shot to build strong immunity. For others, your protection wears off over time. And some viruses change, or mutate, over time, making your vaccine less effective.

For most vaccinations, you need one more jab after the initial series to get more protection. This extra dose of a vaccine is known as a booster shot.

A vaccine contains weakened forms of the disease-causing virus or bacteria, or parts of these germs. Or it may be made of an altered genetic "blueprint" for the germ that can make you sick.

The shot triggers your immune system to attack the foreign organism, like it would if you actually got the disease.

This helps your immune system "remember" the disease-causing germ. If you’re exposed to it again, the antibodies can recognize and kill it before it causes harm.

Research has shown that booster shots train your body to recognize the virus or bacteria and defend itself. Depending on the type of vaccine and the manufacturer, you might get a booster weeks, months, or even years after your first shot.

You may get booster shots as a baby, teen, or adult. You may also need to re-up some vaccinations depending on your lifestyle, travel, or job (for example, if you're a health care worker).

Vaccine boosters that children need include:

Vaccine boosters you may need as a teen or adult include:

Experts recommend that both children and adults get the seasonal flu shot each year. While it’s not 100% effective, it may prevent severe illness. Flu shots are especially important for pregnant women, older adults, and those who have chronic conditions like diabetes or high blood pressure.

During each pregnancy, women need the Tdap vaccine to protect against whooping cough. You usually get it between weeks 27 and 36 of your pregnancy. Along with the flu and Tdap vaccine, health care workers should stay up to date on their hepatitis B, MMR, chickenpox, and meningitis shots.

International travelers may need certain vaccines, depending on their destinations. Antibodies from these vaccines wear off over time, so make sure you're up to date on vaccines for diseases like typhoid. The CDC's Traveler's Health page can help you find out which ones you need.

If you’re not sure which disease you need a booster for, ask your doctor.

Most people who got a vaccine against COVID-19 are already protected against serious illness from the coronavirus. Much depends on whether you are already immunocompromised.

But even highly effective vaccines often become less effective over time, and the coronavirus vaccines are no exception. Initial evidence on mRNA vaccines like Pfizer and Moderna suggest they start to lose some of their power against infection and serious illness, regardless of variant of the virus (i.e. Alpha, Beta, Delta, Omicron, etc.).

None of the updated 2023-2024 COVID-19 vaccines is preferred over another and the CDC recommends the updated COVID-19 vaccines: Pfizer-BioNTech, Moderna, or Novavax, to protect against serious illness from COVID-19. 

It suggests that everyone aged 5 years and older get one dose of an updated COVID-19 vaccine to protect against serious illness. Children aged 6 months–4 years need multiple doses of COVID-19 vaccines to be up to date, including at least 1 dose of updated COVID-19 vaccine. 

Those who are moderately or severely immunocompromised may get additional doses of the updated COVID-19 vaccine.

People aged 65 years and older who received 1 dose of any updated 2023-2024 COVID-19 vaccine (Pfizer-BioNTech, Moderna, or Novavax) should receive one additional dose of an updated COVID-19 vaccine at least 4 months after the previous updated dose. 

COVID-19 vaccine recommendations will be updated as needed.