Now that the CDC recommended booster doses of all three U.S.-approved COVID-19 vaccines, many may be wondering how exactly the agency concluded that those who've been vaccinated can get a booster shot made by a different company than their initial regimen.

The boosters give "flexibility" to the vaccinated, according to Dr. Shobha Swaminathan, Rutgers New Jersey Medical School associate professor, and are safe and effective as indicated by clinical trial data.

Not only that, Swaminathan said, but in those whose antibody levels may have decreased since receiving their primary vaccine series, a booster — in keeping with its name — can restore those levels to what they were, or even higher.

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Swaminathan said preliminary research even suggests that for those who got the one-dose Johnson & Johnson vaccine, following up with one of the other makers' shots, something called heterologous boosting, may produce more antibodies than a J&J booster would.

"If you initially got the J&J vaccine, you might probably be better off getting a booster with one of the messenger RNA vaccines, either the Moderna or the Pfizer vaccine," Swaminathan said.

In the primary series stage, Johnson & Johnson was seen to have an advantage because it was one-and-done. But now, the CDC has recommended boosters for all who received that brand, instead of for just the high-risk groups who got the others.

"Since everybody who got the one-and-dones needs to get a 'second shot,' or a booster, it's a level playing field, because you could get a booster with one shot," Swaminathan said.

So what about being "fully boosted"? Full antibody protection is considered achieved two weeks after receiving the Johnson & Johnson shot, or a second dose of Moderna or Pfizer.

But the immune response to a booster could be observed in as little as 10 days, Swaminathan said, because contrary to getting the initial doses, those who have been vaccinated now have a baseline of COVID antibodies to build upon.

"You really needed to wait for the full two weeks after your second shot to be 'fully protected,' right?" she said. "But currently, those that are going in for boosters are not starting from zero."

Swaminathan suggested that the antibody response created by the Pfizer and Moderna vaccines, despite the breakthrough cases caused by the Delta variant, has been so strong that boosters are not being urged at this time for recipients with no underlying conditions.

Still, she said lining up for an extra shot isn't totally worthless for these people.

"We all know of people in our circle, young, healthy people who want to get the booster, and that's OK. And I think these data show that you're not going to have any significant bad outcomes thus far," Swaminathan said.

If you have questions, Swaminathan said to talk to your doctor, read up on the latest CDC guidance, and if you do get a booster shot and have an adverse side effect, report it.

The booster decisions that have been made are the right ones, she said, but were based on much smaller studies, so more information is always needed.

Patrick Lavery is New Jersey 101.5's afternoon news anchor. Follow him on Twitter @plavery1015 or email

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