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 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 will get booster doses every 2–3 years. It is also recommended during an outbreak (when a disease happens in greater numbers than expected in a particular area), with a booster dose given a year later if the outbreak continues.
• DTaP/Tdap: This vaccine is given as a series of 5 injections when kids are 2 months–6 years old. They get booster shots at age 11–12, 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 injections when they're 2 months–6 years old. People 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. They also recommend that everyone age 6 months or older get an updated COVID-19 vaccine for the 2023–24 season. The number of additional doses kids need this season depends on their age, health status, and how many COVID-19 vaccines they've already had. It also depends on whether they get the vaccine made by Pfizer-BioNTech or the one made by Moderna. Some children may need as many as 3 shots this season, spread out over a few months, while others may only need 1 shot.

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 in order to fight the viruses as they change over time. They don’t just boost previous immunity — they provide new immunity. So instead of “booster shots,” health care 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 you might still hear people refer to them that way.