If You Want a Booster, Don't Wait This Long, Experts Warn

You might not want to put off your appointment if you're already eligible.

Millions of people are now eligible for an additional COVID vaccine shot, with select Moderna and Pfizer recipients eligible to get an additional dose at least six months after their second dose, and all Johnson & Johnson recipients able to get their booster at least two months after their initial shot. More than 15 million people in the U.S. have already gotten a booster dose, according to the latest data from the Centers for Disease Control and Prevention (CDC). It's only been about a month since the U.S. Food and Drug Administration (FDA) authorized the first booster vaccine from Pfizer, while Moderna and Johnson & Johnson boosters were approved less than two weeks ago, so it's clear people are eager for additional shots. But if you've been putting off making an appointment yourself, you might want to move forward sooner rather than later. While the CDC and FDA say you can get your booster at any point, some experts caution against waiting too long.

RELATED: Dr. Fauci Says This Is How to Decide Which Booster to Get.

Gary McLean, PhD, a professor of molecular immunology at London Metropolitan University, recently told Business Insider that waiting too long to get a booster if you're eligible might not be beneficial. "Five, six months after double-jab, immunity tends to wane, and it's a good time for a booster," he told the news outlet.

Six months after getting the AstraZeneca vaccine (which is a two-dose vaccine not available in the U.S.), McLean said he got antibody tested and found that his levels were "really low." In the U.S., that's a similar timeline for the Pfizer vaccine. An Oct. 6 study published in The New England Journal of Medicine found that the antibody response produced by Pfizer's vaccine was "substantially decreased" six months after the second dose. And another study, published Oct. 16 in The Lancet, found that the effectiveness of Pfizer's vaccine against infection dropped from 88 percent to 47 percent after five months.

Originally, health experts were planning for an eight-month timeline between a second shot and the booster. But the new research indicating that Pfizer's protection might drop sooner helped push the U.S. government to a shorter timeline.

According to McLean, you might be fine extending your wait time to eight months "without hopefully too many dramatic effects," but getting your additional dose after two mRNA shots as close to the six month-mark as possible is best. "I think tightening it up is better," he added.

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On the other hand, Peter Chin-Hong, MD, an infectious disease expert at the University of California, San Francisco, told CBS-affiliate WREG in September that the six or eight month argument was mostly arbitrary, except for the fact that spacing out your additional dose for at least six months is important.

"The immune system generally does better in terms of 'remembering' if you wait a few months before the last shot," Chin-Hong explained. "If you get all three shots at the same time, or really close to each other, you may not be doing what you set out to do—i.e. train the immune system to remember (how to fight a virus) for many years."

A study published Oct. 15 in The New England Journal of Medicine also found that all three U.S. COVID vaccines—Pfizer, Moderna, and Johnson & Johnson—still showed signs of a strong immune response eight months after their initial series, even without a booster. But in general, many experts say that if you're eligible, it might be best for you to go ahead and get your booster shot before the winter season rolls in, whether it's been six or eight months since your second shot.

Jeanne Marrazzo, MD, the director of the division of infectious disease at the University of Alabama at Birmingham, recently told The Washington Post that boosters are especially important for those at higher risk of severe COVID—older adults and people with underlying medical conditions—as colder weather and the holiday season approaches.

"Winter is coming," she said. "We really want everybody to think about it like topping off your antibody levels, like topping off the tank before winter comes."

RELATED: Don't Get Your Booster at CVS Before Doing This, Pharmacy Says.

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