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Your Guide To Adult Vaccines

8 Things to Know About COVID-19 Booster Shots

Extra vaccine doses are now available to millions of Americans. Here's the latest on what to expect

A nurse marks a coronavirus vaccination card with a third "booster" dose of the Pfizer COVID-19 vaccine in Pasadena, Calif.

ROBYN BECK / Getty Images

A nurse marks a vaccination card with a third dose of the Pfizer COVID-19 vaccine.

En español | Millions of Americans who had the Pfizer-BioNTech vaccine are now eligible for a booster shot, which is meant to wake up the immune system so it stays sharp if confronted with COVID-19. And boosters for Moderna and Johnson & Johnson vaccine recipients will likely be here soon.  

Here’s what you need to know about these additional doses as the shots roll out:

1. Boosters are available, but not everyone qualifies right now 

Nearly 188 million Americans are fully vaccinated, according to the Centers for Disease Control and Prevention (CDC), but only a portion of this population can get a booster shot at this time. That’s because Pfizer is the only vaccine maker authorized by the U.S. Food and Drug Administration (FDA) for boosters, so the additional doses are currently limited to the roughly 100 million Americans who were fully vaccinated with Pfizer’s product. 

What’s more, the CDC is recommending that only some Pfizer vaccine recipients get the booster, including adults 65 and older, people living in long-term care facilities and people 50 to 64 with underlying medical conditions. The booster should be administered at least six months after completion of the primary vaccine series, so people vaccinated during the spring and summer still need to wait to meet this mark. 

Individuals ages 18 to 49 with chronic health issues and people over 18 whose work puts them at high risk for COVID-19 can also get a Pfizer booster, depending on their individual risk of getting COVID and the benefit another shot could provide, the CDC says. Young and otherwise healthy adults whose jobs don't put them at risk are encouraged to hold off on a booster shot for now. 

2. Moderna and J&J boosters could here soon

The wait for boosters could soon be over for people who initially received the Moderna and Johnson & Johnson vaccines. Both companies have requested emergency use authorization from the FDA, and the agency’s advisory committee voted on Oct. 14 and 15 in favor of authorizing the products. The panel recommends authorizing Moderna’s booster for people 65 and older and those at high risk for COVID-19 due to an underlying health condition or their work, at least six months after the initial series is completed. And it’s endorsing an authorization for J&J’s booster for people 18 and up, at least two months after the first shot. 

If the FDA accepts its committee’s recommendations and gives the green light for these two booster products, a similar process will take place at the CDC. Its advisory committee will review and debate the data before offering its recommendations to the agency. An official OK from the CDC’s chief signals that the shots can go in arms.


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3. Booster shots could rev up waning protection in some  

While the coronavirus vaccines can help to thwart infection (vaccinated people are eight times less likely to get COVID-19 than unvaccinated individuals, according to the CDC), their primary function is to prevent serious illness, explains Anna Durbin, M.D., a vaccine and infectious disease expert at Johns Hopkins Bloomberg School of Public Health. And the COVID-19 vaccines are still highly effective at doing just that — they’re keeping people out of the hospital and preventing them from succumbing to the disease. Very few fully vaccinated Americans have been hospitalized or have died from COVID-19 — about 0.009 percent, according to the most recent data.

That said, multiple studies show that some populations are starting to see protection against disease dwindle, including older adults, who account for the majority of the severe breakthrough infections. And top public health experts have said that the current protection could continue to diminish in the months ahead, “especially among those who are at higher risk or were vaccinated during the earlier phases of the vaccination rollout.”  

It’s not unusual to see this waning response. “Even highly effective vaccines become less effective over time,” U.S. Surgeon General Vivek Murthy, M.D., explained in a White House COVID-19 task force briefing. And other vaccines require booster shots to wake up the immune system, like the tetanus, diphtheria and pertussis (Tdap) vaccine.

Israel started administering booster shots to its 60-plus population this summer and has seen a significant reduction in the risk of infection and severe disease, Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, explained in a recent briefing.

Many experts argue the data isn’t strong enough to support booster shots for younger populations who are showing a slower decline in immune protection — at least right now. “And we shouldn't be giving a valuable resource just because we can,” Durbin says about booster doses for everybody. “It really needs to be indicated, I think, by the epidemiology of the disease and of the illness,” she notes, adding that the science could change.

4. Don’t expect any new or unusual side effects

Let’s start with booster that’s already been authorized: The Pfizer data reviewed by FDA shows that booster shots do not appear to have different safety risks than the first two vaccine doses, Mark McClellan, M.D., a former FDA commissioner and director of the Duke-Margolis Center for Health Policy at Duke University, told AARP in a statement. And evidence on boosters from Israel and elsewhere “seems to show benefits in people who are older or are at higher risk of serious complications because of health conditions, without unusual side effects,” McClellan adds.

Pfizer’s booster trial reported symptoms similar to what some people experienced after their first and second doses: temporary pain at the injection site, fever, chills, headache, fatigue, vomiting, diarrhea, and joint and muscle pain. And data presented on Sept. 22 by a vaccine safety group within the CDC’s advisory committee found that a third dose of the mRNA vaccines brought on fewer side effects than the second shot.

An FDA review of Moderna’s booster data details similar findings. The booster — which unlike the other brands, is half the dose of the first two shots — caused side effects similar to those seen after the second dose of the vaccine. The most common among adults 65 and older were injection site pain, fatigue, headache, muscle aches and joint pain. No serious adverse events or serious safety concerns were reported. 

When it comes to J&J booster shots, about 40 percent of clinical trial participants 60 and older reported pain at the injection site after the shot, an FDA review of the data shows. Roughly 29 percent experienced headache and fatigue, about 26 percent noted muscle pain, 12.4 percent had nausea, and 2.3 percent had a fever.   

5. Hold off on mixing and matching vaccines — for now

A lot of people are asking, “Does it matter if I mix and match the brands?” 

The current advice from experts on so-called mixing and matching is to stick with the same vaccine for your booster that you had the first time around. However, this could change. A new study funded by the National Institutes of Health (NIH) found that J&J vaccine recipients who were boosted with either the Pfizer or Moderna vaccine saw a spike in antibody levels much higher than those boosted with the J&J vaccine, which suggests an increase in protection. What’s more, no safety concerns were identified. 

This data, which has yet to be peer reviewed, was presented to the FDA’s advisory committee on Oct. 15, but no action regarding authorization has been taken.

6. Booster doses should be widely available   

Wondering how you can get your booster shot? The same way you got the first shot: Health clinics, pharmacies and other official vaccination sites will continue to administer the COVID-19 vaccines, as well as the boosters. You may need an appointment, so it’s good to check ahead of time.

Health officials have confirmed that the government has adequate supplies, so no shortages are expected. And just like the initial series, the booster shots will be free in the U.S. — no ID or insurance card is required. It is, however, a good idea to bring your paper vaccination record so the date of your booster shot can be added.

“The bottom line is that we are prepared for boosters and we will hit the ground running,” said Jeffrey Zients, White House coronavirus response coordinator. 

7. It’s unclear whether boosters will be needed annually

Experts aren’t sure if the COVID-19 vaccine will be needed on a regular basis, like the flu shot. One thing that could make that scenario more likely, Durbin says, is “if we are unable to control this pandemic — if we continue to see surges that are requiring hospitalization and really taxing health care systems.”


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However, if we can control the spread of COVID-19 and bring down the levels of severe disease we’re seeing, “we may not need booster shots every year,” Durbin adds. “But a lot of that is going to depend on the epidemiology of the pandemic.”

8. There could be a new standard for 'fully vaccinated'

Now that boosters are available, our definition of “fully vaccinated” could change. Currently, people are considered fully vaccinated if they have had two doses of the Pfizer or Moderna vaccines or a single dose of the J&J vaccine.   

“I anticipate, over time, that may be updated,” CDC Director Rochelle Walensky, M.D., recently said in a COVID-19 news briefing. “But we will leave that to our [CDC Advisory Committee on Immunization Practices] to give us some recommendations.”

So stay tuned.

​Who Qualifies for Pfizer’s Booster Shot?

The CDC recommends the following people get a COVID-19 booster at least six months after getting shots one and two in the Pfizer-BioNTech series:

  • People 65 years and older and residents in long-term care settings. 
  • People ages 50–64 years with underlying medical conditions.
  • People ages 18–49 years with underlying medical conditions, based on their individual benefits and risks.
  • People ages 18–64 years who are at increased risk for COVID-19 exposure and transmission because of their occupation (i.e., health care workers, teachers, grocery store employees), based on individual benefits and risks.

Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.

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