Confused About COVID-19 Boosters?

John Whyte, MD


November 15, 2021

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JOHN WHYTE: Are you confused about whether you should get a COVID vaccine booster shot? Let me help try to unpack it for you. Why do some people need boosters? Although COVID-19 vaccination remains effective in preventing severe disease, more and more data suggest vaccination is less effective at preventing infection or milder illness with symptoms over time. Basically, our protection decreases over time. We still have a lot of virus circulating, so we need to protect ourselves, our families, and our communities.

Who's eligible for a booster? If you got Pfizer or Moderna, you're eligible for a booster if you're 65 years of age or older. If you're age 18 or older and you live in a long-term care setting. If you're age 18 and older and you have underlying medical conditions. If you're over the age of 18 and you work or live in high-risk settings, such as a grocery store or health care setting.

When to get a booster? At least 6 months after your second shot. If you received Johnson & Johnson's Janssen, you're eligible for a booster if you're 18 years of age or older. There aren't any limitations based on age or health conditions. Basically, if you got the J&J, you should get a booster. When to get a booster? At least 2 months after your shot.

As for which vaccine shot you should choose, most people like me are sticking with the original one they got. I got Moderna, and that's what I'm sticking with. And the booster for Moderna is half the dose.

Others prefer to choose a different one. We really don't know if one vaccine is truly better than the other. The key is to consider getting a booster if you're eligible, and not worry too much about which one it is.

In case you're wondering, you're still considered fully vaccinated 2 weeks after the second dose in a two-shot series, such as Pfizer or Moderna vaccine. Or 2 weeks after a single-dose vaccine, such as the J&J Janssen vaccine.

Now, there is one other category: people who are immunocompromised. Who's considered immunocompromised? This includes people who have cancer and are getting treatment. People who got solid organ transplant and taking immunosuppressive therapy. People with advanced or untreated HIV infection. People who take certain medicines for conditions like rheumatoid arthritis or Crohn's disease.

You might remember that people who are immunocompromised and received Pfizer or Moderna were eligible to receive a booster with either vaccine back in August. We did that because we learned through studies that if you have a compromised immune system, one or two shots aren't going to work as well because your body can't mount the same degree of response. And that puts you at risk of infection.

Now we recommend that these folks consider getting a fourth dose. The purpose of the fourth dose is the same for people who are not immunocompromised: Combat decrease in immunity. Does get a little confusing since the third dose is now not considered a booster, but rather a part of their primary vaccination series if you're immunocompromised.

I do hope that helps to clear everything up. If you're still having questions, drop me a line at

This interview originally appeared on WebMD on November 15, 2021

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