What you need to know about COVID-19 boosters

Health officials are developing a plan to begin offering COVID-19 booster shots to all people in the U.S. as soon as this fall to maximize vaccine protection.

The Mayo Clinic News Network team sat down with Dr. Melanie Swift, co-chair of the Mayo Clinic COVID-19 Vaccine Allocation and Distribution Work Group. In this Q&A, Dr. Swift answers questions about COVID19 booster shots:

What is a booster vaccine?

A booster vaccine is intended to be a reminder to your immune system. Right now, we’re in a situation where we can see that over time immunity that people achieve from the COVID-19 vaccine does start to wane.

The good news is that it’s waning mostly against mild infection. We still do have protection from those early vaccine doses against severe infection. But we want to stop transmission and we want to keep people from getting any form of infection. So boosters are going to be recommended for everyone.

How is a booster different from an additional dose, which has been recommended for people who are immunocompromised?

They’re really different things with different purposes. The primary vaccination series is intended to build an initial immune response.

Think of it like painting your house. You sometimes can get good coverage with one coat of paint, but occasionally you might need three coats of paint to get that good coverage. It’s the same way with vaccines. Some people might have a great response to one dose, but most people need two doses of the messenger RNA vaccines to get a great response.

But what we’ve learned is that some people actually need a third dose to get a better response to that initial vaccine. And those people are immunocompromised. Their immune systems aren’t working very well, and they do need additional doses of vaccine to respond.

Over time, once you’ve achieved that initial response, your immunity may still wane and you could need a booster. So you might need another coat of paint down the road when the initial one starts to wear thin or get stains on it. Giving another coat of paint is like giving a booster.

Will the booster shots be the same vaccine?

Right now, we are giving that third dose and planning to give that booster dose with the same formulation of the original vaccine. But that could change over time.

The manufacturers — Pfizer and Moderna — are studying variants of that initial messenger RNA vaccine that can be designed to cover mutations that some of the variants of concern are exhibiting. It may be that we get annual boosters, and over time each year, that might be a different vaccine that helps provide better protection against the coronavirus strains that are currently circulating — much like we do with flu vaccine.

We already have this concept. We get a new flu vaccine every year, and it covers different strains than previous years.

What will be the possible side effects of a third dose?

So far, it looks like this side effect profile from a third dose is very similar to what was experienced with a second dose — not any worse and perhaps a little milder. That probably has to do with the time that’s elapsed since you last had that vaccine.

Getting that initial series, you’re taking a vaccine three or four weeks after you just had it and your immune system is really responding robustly, giving people more of those side effects. But after months later, with a booster dose, it doesn’t look like there’s any more robust immune symptoms that people would have. They can expect to have those typical vaccine side effects: a headache, they could feel tired, they could have a low-grade fever, they could have some muscle aches. And those still happen really quickly and resolve on their own within two to three days.