You have COVID booster shot questions. We have answers.

·12-min read

This week, the Centers for Disease Control and Prevention endorsed COVID-19 booster shots of the Moderna and Johnson & Johnson vaccines, as well as a mix-and-match approach that will allow tens of millions of Americans to get COVID-19 vaccine booster shots and offer them the flexibility to choose a shot that is different from their primary series.

CDC Director Dr. Rochelle Walensky signed off on the measure late Thursday following a CDC advisory committee’s recommendation that Americans be allowed to choose among all three available COVID-19 booster shots. Before this decision, only Pfizer recipients and immunocompromised patients were eligible for the booster shots, but now many more Americans will be able to seek theirs out as early as Friday.

“These recommendations are another example of our fundamental commitment to protect as many people as possible from COVID-19,” Walensky said in a statement. “The evidence shows that all three COVID-19 vaccines authorized in the United States are safe – as demonstrated by the over 400 million vaccine doses already given. And they are all highly effective in reducing the risk of severe disease, hospitalization and death, even in the midst of the widely circulating Delta variant,” she added.

Yahoo News spoke recently to Dr. Lucy McBride, who specializes in internal medicine, to break down what Americans need to know about boosters and the new mix and match approach.

Why are boosters necessary?

According to McBride, “COVID-19 boosters are necessary to optimize the immune protection for our highest risk populations” as well as “protect people from death and severe disease from COVID-19.”

As the Delta variant of the coronavirus has spread around the world, U.S. and international data, particularly from Israel, has shown vaccine effectiveness declining over time. This reduction in protection is significant for those age 65 and older in particular.

Last month, the CDC first approved boosters for recipients of the Pfizer vaccine after the company submitted compelling data that suggested a decline in vaccine effectiveness against infection, hospitalization and death over time.

The data on vaccine effectiveness for the Moderna vaccine presented to the CDC this week, however, suggests the shot remains highly effective against serious illness and death in most people under 65. But the CDC committee said Thursday one of the reasons it was important to endorse and expand the Moderna boosters to other groups is because recommending boosters for Pfizer recipients only created inequity for recipients of the other two vaccines.

When it comes to the Johnson & Johnson vaccine, experts expected long ago that booster doses would be necessary, as the vaccine effectiveness for this shot has been shown to be consistently inferior in numerous studies compared to the mRNA vaccines.

According to a CDC report published last month, for example, vaccine effectiveness against COVID-19 hospitalization from March 11 to Aug. 15, 2021, for the Johnson & Johnson vaccine was only 71 percent compared to that of the Moderna vaccine (93 percent) and the Pfizer-BioNTech vaccine (88 percent).

McBride and other experts, however, emphasize that the need for boosters does not mean that the current vaccines do not work. On the contrary, recent studies show that those who aren’t vaccinated are five times more likely to be infected, 10 times more likely to be hospitalized and 10 times more likely to die from COVID-19 than those who are vaccinated.

“The reason some people need booster shots, despite the extraordinarily high effectiveness of the vaccines, is because there is a very tiny percentage of people who, if exposed to the coronavirus and get a breakthrough infection, are at particularly high risk for poor outcomes. So we’re really trying to protect those most vulnerable populations without confusing the general public and suggesting that the vaccines aren’t supremely effective,” McBride said.

How effective are the booster shots?

McBride said that boosters help optimize our antibody levels, as well as our T-cells and our memory B cells, which play an important role in building immune responses against viruses.

“We know from real-world data that the booster shots do an excellent job at adding protection for our most vulnerable populations,” McBride told Yahoo News.

But now there’s also scientific evidence to support that claim. A recent study conducted by Pfizer and published on Thursday also found that boosters are extremely effective. Results from the first randomized controlled trial of a booster conducted by the pharmaceutical company of more than 10,000 people suggests that a booster dose of its COVID-19 vaccine is 95.6 percent effective against the disease compared with those receiving two shots and a placebo. The study also found that the booster dose was effective regardless of age, sex or race.

Who is eligible for a booster shot now?

People fully vaccinated at least six months ago with the Pfizer or Moderna mRNA COVID-19 vaccines who are at least 65, or who are at least 18 and at high risk of severe COVID-19 due to underlying medical conditions could receive a booster shot.

A complete list of those medical conditions can be found on the CDC’s website.

For those with a condition that is not listed on the CDC’s website, but may still be at greater risk of severe illness from COVID-19, the agency recommends consulting with their health care provider to discuss whether or not they may benefit from one of the boosters now available.

Also included in the updated CDC recommendations are individuals 18 and older who have frequent institutional or occupational exposure to the virus such as health care workers, teachers and grocery store employees, as well as those who live in high-risk settings such as long-term care facilities.

The full list of groups who qualify can also be found on the CDC’s website, and the agency’s director said at a White House COVID-19 response team press briefing on Friday that eligibility may expand in the future as more data becomes available.

“We are following the data in real time and we are looking at its ongoing efficacy, as well as the potential for waning in our other age groups, and we will update our recommendations as soon as we have more data for recommendations for other age groups,” Walensky said Friday.

COVID-19 vaccine boosters were first approved in August for people with compromised immune systems who received either the Pfizer or Moderna mRNA vaccine.

This segment of the population, which comprises about 3 percent of Americans, is more vulnerable to COVID-19 due to weakened immune systems. For this reason, the CDC recommends that this group receive a booster shot within one month after their primary series.

What are the latest recommendations on booster shots? What does “mixing and matching” vaccines mean?

Americans under the categories above who are fully vaccinated with the Pfizer or Moderna mRNA vaccines are now eligible to receive a booster six months after their primary series. To be considered fully vaccinated, one must receive two doses of the mRNA vaccines or one shot of the Johnson & Johnson shot. For those receiving the mRNA vaccines, it is recommended that both shots that constitute the primary series be of the same brand.

The Pfizer and the Johnson & Johnson booster doses are exactly the same as the primary doses. The Moderna COVID-19 single booster, on the other hand, consists of half of the dose (50 micrograms) that is administered for a primary series dose. However, those who are immunocompromised are recommended to get a full dose (100 micrograms) of the Moderna shot as a booster.

For the almost 15 million people who were initially inoculated with the one-dose Johnson & Johnson vaccine, both the FDA and the CDC recommended they get a booster shot two months after receiving their first shot.

Americans eligible for boosters will now have the flexibility to choose any of the three authorized vaccines to better protect themselves. The clinical term for mixing and matching vaccines is called “heterologous.”

For example, those who received the Johnson & Johnson vaccine may receive a single booster dose of the same COVID-19 vaccine, Moderna (half dose) or Pfizer vaccine at least two months after receiving their Johnson & Johnson primary vaccination.

Furthermore, Americans who received the Moderna and Pfizer-BioNTech mRNA vaccines that fell into one of the authorized categories for boosters may receive a booster dose of the Moderna (half dose), Pfizer or Johnson & Johnson vaccine at least six months after completing their primary vaccination.

Which booster should I choose?

There’s not a clear consensus regarding which booster people should pick. CDC Director Dr. Rochelle Walensky said at a White House COVID-19 briefing on Friday that the agency “will not articulate a preference.”

However, White House chief medical adviser Anthony Fauci told CNN on Friday that even though Americans can now choose a COVID-19 booster shot that is different from their original shot, the recommendation is to stick with the vaccine they got first if it is available.

“It’s generally recommended that you get the booster that is the original regimen that you got in the first place,” Fauci said.

“But for one reason or other — and there may be different circumstances with people, availability or just different personal choices — you can, as we say, mix and match,” Fauci added.

McBride told Yahoo News that she is making certain recommendations to patients based on their specific needs. For example, there’s a blood-clotting disorder, thrombosis with thrombocytopenia syndrome (TTS), which has been associated with the J&J vaccine. Although it is rare, it has caused severe illness and even death in a handful of cases. Women under 50 seem to be most prone to TTS, McBride says, so for patients in this age group who are at higher risk in general for blood clots from this shot, the advice is to get a single mRNA dose for their vaccine booster.

Similarly, there is a condition called myocarditis, which is an inflammation of the heart muscle that has been associated with the mRNA vaccines. These cases are very rare and have been most commonly reported among young men after a second dose. McBride says “men ages 18 to 24, who are at higher risk for vaccine-induced myocarditis from the mRNA vaccine, are the people who don't really necessarily need a third dose,” unless they are immunocompromised. In that case the internal medicine doctor says she would choose a Johnson & Johnson booster for that patient “because of the rare but real side effects of myocarditis.”

If you are eligible and not sure which booster you should receive, experts recommend having a conversation with your health care provider to better understand the risks and benefits of each shot.

But McBride said we should feel confident in the effectiveness and safety of these vaccines.

“In terms of mixing and matching vaccines, I think we need to keep a sight of the big picture, that these are extraordinarily effective vaccines, and it would almost break our understanding of immunology to think that the Pfizer and Moderna were that different in terms of being that brand for your third vaccine dose. So I think we are seeing some mixed messaging, but at the end of the day, whichever vaccine you get as your third dose, if you are eligible, is going to offer wonderful protection.”

What is the advantage of mixing and matching booster shots?

The data is not so clear, but some studies have suggested that mixing and matching vaccines may offer better protection. Several research groups have found that mixing one dose of AstraZeneca, which is a vaccine that uses a similar technology to the Johnson & Johnson vaccine, with either one dose of Pfizer or Moderna induces a stronger immune response than two doses of the same vaccine.

In addition, a recent National Institutes of Health study, which influenced the FDA and the CDC decision to endorse the mix and match strategy, found that for recipients of the Johnson & Johnson vaccine antibody levels rose 76-fold after a Moderna booster and 35-fold after a Pfizer booster, compared with fourfold after a J&J booster.

Leana Wen, an emergency room physician and the author of “Lifelines: A Doctor’s Journey in the Fight for Public Health,” told Yahoo News that the ability of mix and matching also offers great flexibility to local health departments, pharmacies and other vaccine providers who are now able to more rapidly administer boosters. She adds that it also empowers people to choose based on their preferences and medical circumstances.

“The convenience of accessibility is really important because we’re in the middle of a pandemic. We need to get booster shots out to meet many millions of people,” Wen said. “If we had to match the exact brand, and every provider had to carry all three brands of the vaccines, that would delay things, and it would delay the booster rollouts and in particular will hurt those who have less access to care to begin with,” she added.

What are the side effects?

McBride said the side effects of the booster shots are similar to those from the primary series. The most common symptoms include fatigue and pain at the injection site, but most symptoms are mild to moderate.

“We need to be transparent about the side effects,” McBride said. Those symptoms post-vaccine, she said, “are normal and expected and evidence of your immune system working appropriately.”

When and where can you get a booster shot? Are they free?

If you are eligible under the categories mentioned above, you can receive a booster shot as early as Friday, Oct. 22.

At Friday’s press briefing, Jeff Zients, White House pandemic response coordinator, said thousands of locations, including pharmacies, grocery stores and community centers across the country, are ready to offer the booster shots to tens of millions of eligible Americans.

For more information about eligibility and locations, visit

All COVID-19 vaccines are free in the United States and no health insurance or ID are necessary to receive the shot.


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