Skip to main content

Health library

Back to health library

Who needs an additional COVID-19 shot?

A woman in a face masks walks down a sidewalk. COVID-19 vaccines have been very good at keeping most fully vaccinated people out of the hospital. But that's not always been the story for people with weakened immune systems.

Not only do they face a higher risk of severe illness from COVID-19, but their bodies may not mount as robust of an immune response to the vaccines. That leaves them more vulnerable to breakthrough infections.

That's where an additional shot comes in. The Centers for Disease Control and Prevention (CDC) now recommends a third dose of mRNA vaccines for some people with weakened immune systems. Studies suggest the extra dose may help increase their protection. This additional shot is different from a booster shot.

Who needs a third shot?

About 3% of adults in the U.S. are moderately to severely immunocompromised. If you're one of them, CDC recommends getting an additional shot if it has been at least 28 days since your second dose of either the Pfizer or Moderna vaccine. (CDC says they don't have enough data yet to recommend an additional shot to people who got the Johnson & Johnson [J&J] vaccine. But they expect to know more about that soon.)

You may be eligible for an additional shot if you:

  • Are being treated for cancer.
  • Have a condition that lowers your immunity, such as advanced HIV.
  • Have had a stem cell transplant in the past two years.
  • Take high doses of steroid drugs.
  • Take other drugs that suppress your immune system, including after an organ transplant.

If you're not sure if you should get an additional shot, talk to your doctor.

What about everyone else?

While the vaccines have been effective against severe illness so far, there is some concern that their protection may fade over time. So CDC also says that all adults who received the Pfizer or Moderna vaccine are eligible for a booster 6 months after their initial series.

People 18 and older who received the J&J vaccine are eligible 2 months after their initial shot.

Your booster does not have to be the same as the vaccine you originally received. You can stick with the same vaccine if you want, or you can choose one of the other available vaccines.

If you have questions about what's right for you, talk with your doctor.

You can learn more about all three vaccines in our Coronavirus topic center.

Reviewed 11/22/2021

Read more breaking news Related stories