2nd boosters: what do we know?


A: With BA.2 on the rise, getting your next booster shot if you’re eligible (50+ or immunocompromised, in the U.S.) can keep your protection high with little downside.

What we know right now is that a second booster shot poses few risks, but the benefits vary from person to person. And we don’t yet have a perfectly clear picture of who will benefit the most from a 4th shot. The higher your risk of severe outcomes from COVID-19, the more you stand to gain from another booster.

We’re going to do an in-depth review of this subject, so buckle up for a long post.

✨ Who can get another booster?

In the United States, eligibility for a second booster shot now includes any adult age 50 and older and anyone who is moderately to severely immunocompromised. J&J recipients who already got one mRNA booster are eligible for another one if you are 50+ or immunocompromised. And all J&J recipients who also got a J&J booster are also eligible for another (mRNA) booster.

You are considered moderately to severely immunocompromised if you:

💊 take chronic medication that suppresses your immune system (like steroids used long-term)
💊 have had an organ or bone marrow transplant
💊 have untreated HIV
💊 have a genetic primary immunodeficiency syndrome
💊 are actively being treated for cancer with chemotherapy

This is very different in other places. For example in EU countries, a 4th shot is only available to people who are over age 80 at this time.

✨ What is the evidence that a booster is needed?

TBH it’s pretty slim at this point. Broadly speaking, there is little (or no) evidence that immunity is waning among *most* people who have had their primary vaccine + one booster.

However, not every person in the general population has the same level of immunity. Our immune systems become less responsive with age, and some of us have weak immune systems for reasons other than age. As the pandemic goes on (and on, and on) we want to offer as much protection as possible to those who have the highest risk of their vaccine failing. We can think of the 4th booster as an extra layer of protection just for those who may need it, at this point.

Israel started giving their older-aged population a 4th dose of Pfizer vaccine a few months ago. Among those people older than age 60 who got a 4th dose, there were fewer deaths than in the same-age population who got just one booster. However, the group that got a second booster wasn’t randomized, so the conclusions we can draw from this are limited.

Another study out of Israel looked at the benefits of 2nd booster shots in a relatively healthy, younger population of healthcare workers. Some study participants got a 4th shot. These were matched to controls who had three shots. In this study, the benefit of a 4th dose was marginal or nonexistent. There were no cases of severe disease in either group, and the 4th dose only protected against mild disease a tiny bit. Both studies were conducted when Omicron was the dominant strain.

Because of these two studies, we think that the second booster is most important for older people and people who have conditions that make their immune system less responsive. For everyone else, at this point there’s little evidence that it is helpful (though, also no evidence that another dose is harmful).

✨ What are the risks of taking another booster?

Very few. They are about the same as taking the first booster: many will have symptoms associated with reactivating the immune system like fever, fatigue, muscle aches or headache. As we know from our first booster, for the majority of people these are mild and can be managed with rest and over-the-counter medications like Tylenol. There is a very small risk of severe allergic reaction, like anaphylaxis. But if you’ve already taken 3 vaccines without an allergic reaction, the risk of a new reaction to the 4th is all but nonexistent.

There is no evidence to support concerns about over-stimulating your immune response with repeating vaccine doses.

The very low risks of a 4th dose are the reason it’s been authorized for people who may benefit the most, even though the evidence for their efficacy is currently slim.

✨ When will the general population need another booster?

If you are younger than 50 and not immunocompromised, we don’t know if or when the recommendation for a second booster will arrive. It could happen, given the way the original vaccine series and first booster dose recommendations were rolled out by age group. We also haven’t yet heard whether health care workers and others at high risk for being exposed to COVID-19 on the job will be recommended to take another booster. The studies from Israel did not show a benefit for hospital workers who are otherwise low risk.

✨ When should I get my 4th dose? Should I wait until right before vacation or the fall back-to-school wave?

There are just too many unknowns to say what the optimal timing is. We don’t know when the next wave is coming. We don’t know how long the immunity boost lasts from a 4th dose. The good news is that the CDC has been proactive about adjusting booster guidelines in response to the latest evidence, and we are optimistic that they will revise again as needed.

✨ Should I wait for a variant-specific booster?

More unknowns! We don’t know when we’ll have variant-specific boosters. But we also don’t know if a variant-specific booster would be more effective at all–so this unknown is not a good reason to wait, particularly if you are at high risk for severe disease from COVID-19.

We DO know that vaccine manufacturers are working on variant-specific boosters and even a combined COVID-flu annual vaccine. It seems very, very unlikely that this is going to be your last COVID shot, so there’s no reason to worry that if you get one now, you won’t be eligible again later. You probably will be.

✨ What if I just had COVID?

If you were among the many hundreds of thousands of people who were sick during the Omicron wave in December-January, you DID get a boost to your immunity. We’ll hopefully know more about this soon as data is collected and studies are put together. For now, if you have recently recovered from COVID, it’s reasonable to wait a few months before seeking another booster.


With BA.2 on the rise, getting your next booster shot if you’re eligible (50+ or immunocompromised) can keep your protection high with little downside.

P.S. There is VERY strong evidence showing that your first booster is important, so if you are still waiting on that one, please get it ASAP!

Stay Safe. Stay Sane.
Those Nerdy Girls

Additional Links:

CDC Press release on boosters

Conditions that increase your risk of COVID-19

Where to get your primary or booster doses

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