Virus Experts Say If You Want a Booster, Don't Do This Right Now

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After months of debating the need for booster shots, the U.S. Food and Drug Administration (FDA) has authorized an additional dose for select recipients of the Pfizer and Moderna vaccines and all of those who initially got Johnson&Johnson's one-dose vaccine. While Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky, MD, still has to sign off on her agency's official recommendations for Moderna and Johnson&Johnson booster doses, millions of eligible recipients are already getting their Pfizer shots. But now that the FDA has just authorized mixing and matching vaccines, some people eligible for the Pfizer booster are weighing their options. For their part, virus experts say this may not be the best idea.

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Jeremy Levin, MD, former chairman of the Biotechnology Innovation Organization and founder of Ovid Therapeutics, says people should get their booster shot as soon as possible and as soon as it is recommended. "Waiting increases the probability that the immunity gained by the original vaccination will diminish," Levin warns.

This is particularly pertinent to at-risk Pfizer recipients who received their second dose at least six months ago, according to J. Wes Ulm, MD, a physician-scientist and medical researcher. Both the FDA and the CDC have already authorized and recommended Pfizer boosters for anyone 65 years and older or those 18 and older with underlying conditions or high risk occupational or institutional exposure to COVID.

"It's best to simply go ahead and arrange the booster if there has been a substantial gap since the second Pfizer vaccine dose and not await further optimization based on Moderna or Johnson&Johnson data," Ulm explains. "This is especially true for vulnerable populations—particularly the elderly and those with multiple comorbidities such as obesity and hypertension."

The only eligible Pfizer recipients who should wait on boosters might be those who had an adverse reaction with either of the first two doses. "As a rule of thumb, a patient who's had an adverse reaction with a previous vaccine may benefit most from talking with their doctors about alternatives," Ulm advises.

This goes for the other two vaccines as well. For example, Vivek Cherian, MD, an internal medicine physician at Amita Health in Illinois, says Johnson&Johnson recipients who experienced a rare blood clot after their first dose wouldn't necessarily want to get an additional shot of that vaccine. "When in doubt it's always a good idea to touch base with your doctor and have a conversation weighing the risks and benefits and then make a decision that works best for you," Cherian advises.

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If you do decide to wait despite already being eligible and having no previous adverse reactions, experts say you can still benefit from talking to your doctor. "It's important to ask your physician for their advice," Levin says, noting that booster doses for all three vaccines have been shown to be effective.

Early data on mixing and matching vaccines from the National Institutes of Health (NIH) and the National Institute of Allergy and Infectious Diseases (NIAID) study has indicated that Johnson&Johnson recipients might benefit more from an mRNA booster, however. According to the study, which was preprinted on Oct. 13 and not yet peer reviewed, Johnson&Johnson recipients who got a Moderna booster had their neutralizing antibody levels rise 76-fold within 15 days, while a Pfizer booster raised their antibody levels 35-fold. A Johnson&Johnson booster only increased the levels 4-fold.

But experts caution against putting too much weight into this study. "We don't have all the data yet, and this one small study only measured antibody levels which don't give us the complete picture regarding a person's immunity," Cherian says.

He adds, "In general we've had data now for a number of months for studies that suggest mixing and matching booster doses have a more robust antibody response than getting a booster of your initial vaccine. That being said, it will take time and more data to know which combinations will prove to be most effective. The takeaway message, though, is if you are approved for a booster, don't wait."

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