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.

What Booster Shots Do People Get and When Do They Get Them?

Booster shots are given for many vaccines that kids and adults get. These include:

• Hib: The Haemophilus influenzae type b vaccine is given to kids in 2 or 3 doses when they're 2–6 months old. They get a booster dose when they're 12–15 months old.
• MenACWY: This meningococcal vaccine is given at age 11–12 years. A booster dose is given at age 16. Kids who have a weak immune system might need to get the primary dose earlier, and then booster doses every few years.
• MenB: This meningococcal vaccine is usually offered as optional at age 16–18, but is recommended as routine for kids 10 years and older who have specific conditions that weaken their immune system. They'll get a booster dose a year after the primary dose and then every 2–3 years for as long as they're at higher risk for meningococcal disease. The vaccine also is recommended if there is an outbreak of the disease (when it happens in greater numbers than expected in a particular area).
• DTaP/Tdap: This vaccine is given as a series of 3 shots when kids are 2, 4, and 6 months old. They get booster shots at ages 15–18 months, 4–6 years, 11–12 years, and then every 10 years. Pregnant women get a booster shot as well.
• IPV: Kids get this vaccine to protect from polio as a series of 4 shots when they're 2 months–6 years old. Adults who are at risk for exposure to polio can get a one-time booster dose.

Are the Flu and COVID-19 Vaccines Considered Booster Shots?

Experts recommend that everyone age 6 months or older:

• get a flu vaccine every year
• stay up to date on their COVID-19 vaccine, which can mean more doses as time goes on

Even though these repeated flu and COVID-19 vaccines work by “boosting” the immune system response, experts don't call them booster shots. That's because they differ from the previous vaccines. They've been updated to fight the viruses as they change over time. They don’t just boost previous immunity — they provide new immunity. So health experts call them the annual flu vaccine and updated COVID-19 vaccine. But COVID-19 vaccines given after the primary series were called booster shots, so some people still call them that.