Your Questions About Booster Shots, Answered

COVID vaccine booster shots were originally limited to people over 65 and others with higher risk, but as of early December, all adults and some adolescents are now eligible.

When should you get a booster? And will it ward off new variants like omicron?

We spoke with David Buchholz, MD, senior founding medical director for primary care at ColumbiaDoctors, and Marcus Pereira, MD, assistant professor of medicine in the Division of Infectious Diseases at Columbia University Vagelos College of Physicians and Surgeons, for answers to frequently asked questions about booster shots.

Why are booster shots recommended?

Pereira: Scientists from the FDA and CDC have closely monitored data and confirmed that vaccine protection may decrease over time. For example, studies in the United States have found that among essential workers, vaccine effectiveness against infection waned in July, though severe disease remained rare.

Are booster shots safe?

Pereira: Yes, booster shots are proven to be safe. Pfizer released a study of 10,000 participants in which half of them received a booster dose and half a placebo. In terms of safety, they found no new adverse events, meaning it was consistent with what has been seen in previous studies. For those concerned about myocarditis or pericarditis, inflammation of the heart muscle or the outer lining of the heart, no cases of either were observed. In fact, the placebo group had more serious adverse events than the booster group.

Who should get a booster shot, and when?

Pereira: A booster shot is now recommended for anyone over the age of 18 who finished their mRNA series [Pfizer or Moderna] at least six months ago or received the Johnson & Johnson vaccine at least two months ago.

By changing the eligibility criteria, the guidance is now less confusing. They’re telling the general public, absolutely get a booster. And the time to do it is now, before the holidays and the new year.

Can you mix and match vaccines?

Pereira: The FDA and CDC now allow for a mix-and-match approach for booster doses. That means that those who are eligible to receive a booster shot have the option of getting any of the approved vaccines. Data show that this is safe and effective and, in some cases, particularly in the case of the J&J vaccine, mixing and matching elicits a stronger immune response.

The National Institutes of Health released a study on mixing and matching that looked at antibody data. It found that the mRNA vaccines resulted in higher antibody titers in the first 28 days after the boost. If you were to really split hairs, getting a Moderna booster looks to produce slightly better antibodies of the three, but not by much compared to Pfizer—it’s almost tied. But if I got the Johnson & Johnson, I’d choose a Moderna or Pfizer booster.

Also, remember this data is based on antibodies, so what it means in the real world is hard to know. It is up to each individual to determine which type of vaccine to get as a booster shot, so I’d recommend speaking to your doctor for more specific guidance.

Will a booster help against omicron?

Pereira: The question of whether prior infection or vaccination is protective against omicron has been on everyone's minds. 

A number of labs throughout the world have been working on this since omicron was identified, and we are now seeing some early reports. The early findings, unfortunately, suggest that omicron is indeed able to evade some antibodies, whether those are formed from natural infection or vaccines.

That being said, it's not all bad news. Most experts think that breakthrough infections should lead to milder symptoms. Even more reassuringly, it seems that booster vaccine doses can significantly improve protection against omicron.

The key here is that, more than ever, we need to get everyone who is eligible vaccinated and boosted. You want to be as protected as much as possible from these new variants, since we still don't know much about them in terms of severity and long-term outcomes.

But obviously there’s still a lot that’s unknown about omicron, and we’ll continue to find out more in the upcoming weeks.

What if I’m immunocompromised? Does the timing of the third shot differ?

Buchholz: People who were immunocompromised when they had their first set of shots never got quite the level of immunity we would hope for, and so we have been recommending for a long time now that they get a third shot. We don't call that a booster; that’s an additional dose. We're trying to keep that language separate and that population separate.

So if you were immunocompromised during the time that you got your first shots, you really should get a third shot as long as it's been a month or more since your second shot. Other adults need a booster if it's been six months since their last dose.

Why should I get vaccinated if the vaccine already needs a booster shot to protect me? Are vaccines not effective?

Buchholz: Three-shot vaccines are very common. And that's why resistance or criticism of a booster doesn’t make sense to a clinician. I'm a general pediatrician, and we give the same shots at 2, 4, and 6 months of age. And then we boost them somewhere between 12 and 18 months of age, we boost them again at age 4, and then we boost them again at 12. This whole concept of boosting immunity against high-risk diseases is well established.

We're constantly boosting. We get boosters for measles, mumps, and rubella before we go to college. We give a booster shot for tetanus, diphtheria, and pertussis (Tdap) to every woman who's pregnant—every time they're pregnant—because we're trying to boost their immunity against pertussis, which is also called whooping cough, so that they're not getting whooping cough and giving it to their baby. We boost all the time.

We know that the vaccine is not perfect; people do get breakthrough infections. But understand that the vaccine is as much about preventing serious disease—that means preventing hospitalization and death—as it is about preventing infection. Our goal with these vaccines is to prevent those more serious cases. And the vaccines are very, very effective in that regard.

Once in a while, you get a celebrity—an actor, an athlete, somebody with a public persona—who will say, “I've been fully vaccinated and I got COVID anyway, and it was serious! I was sick, I was in bed!” And that influences people’s perception of the vaccine and its effectiveness. Yes, there will still be vaccinated people who get sick and need to stay home, drink fluids, and get rest. But they aren't often hospitalized. They don’t often die. That’s the vaccine working. It’s frustrating, because serious COVID cases are still incredibly rare in vaccinated people, but they get a lot of press.

Should we expect more COVID-19 booster shots to follow, like an annual flu shot?

Buchholz: The most common boosters that people think of, of course, are flu boosters. There are changes in the shot most years to adapt to the variant of flu, because flu is constantly creating variants. And so we change the flu shot to a variant booster and we get boosted again. That’s just like if we were to get a fourth booster shot for COVID. Someday, the COVID vaccines probably will be tweaked to adjust to a variant, just like a flu shot is, and that is normal. It's expected. We will continue to boost for as long as the disease is in the community.

If the disease goes away, we'll stop giving COVID shots and we won't need boosters. Smallpox is a perfect example: We gave smallpox shots for decades, but we don't do smallpox shots at all anymore because we eradicated it from the population due in large part to the vaccine.

Is the timing of my booster shot important, relative to other vaccines? Can I get it at the same time as my flu shot, or along with another vaccination, like shingles?

Buchholz: There’s no harm in having them at the same time. When the COVID-19 vaccines first came out, we recommended not getting the vaccine within two weeks of another shot. We needed data to confirm that your immune response to the COVID-19 vaccines wasn’t reduced by getting another shot at the same time. Once we had data that confirmed a COVID-19 shot with another shot on the same day or within two weeks of each other didn’t affect your immune response, we dropped the recommendation.

Side effects are also not additive or worse if you get multiple shots together. Using my pediatric example again, at 2 months of age, we immunize infants against eight different diseases with minimal or no side effects. And it’s convenient to get shots together so you don’t have to schedule multiple visits. I got my Pfizer booster and flu shot on the same day at the same time.

Are people more likely to have fever, aches, etc. (or “vaccine reactogenicity”) after a third dose? How should I prepare for my booster shot?

Pereira: Pain at the injection site and headaches were commonly reported side effects, but the booster dose has been shown to have a lower likelihood of side effects than the second dose.

The CDC has been monitoring injection site reactions and systemic reactions (fatigue, fever, body aches) as well as health impacts, such as the ability to work or perform daily activities. In terms of these factors, the reactions from the booster appear to be less disruptive than the reactions experienced from the second dose.

Buchholz: If those symptoms would potentially disrupt your ability to work, you might want to get the shot the day before a day off, just so that you don't have that issue at work. Be prepared, but know that you may not even get those symptoms, and if you do, you can take some acetaminophen or ibuprofen to help make you feel better.

If I had COVID-19 and am fully vaccinated, do I still need a booster?

Periera: Pfizer did study those who had prior COVID infection, and the data suggests that a booster dose is protective for that population and certainly not harmful.

Closing thoughts?

Buchholz: Booster shots are an important tool but getting everybody vaccinated is even more important.

Tens of millions of eligible Americans have yet to receive a single dose. If you haven't been vaccinated, we are asking you to please get vaccinated for your health and the health of your family.