Health Team

Pfizer data suggest third vaccine dose 'strongly' boosts protection against Delta variant

Posted July 28, 2021 8:55 a.m. EDT
Updated July 28, 2021 7:56 p.m. EDT

— A third dose of the Pfizer/BioNTech vaccine can "strongly" boost protection against the coronavirus Delta variant beyond the protection afforded by the standard two doses, new data released by Pfizer on Wednesday suggest.

The data posted online suggest that antibody levels against the Delta variant in people ages 18 to 55 who receive a third dose of vaccine are greater than five-fold than following a second dose. The effect is even more marked among older adults, according to the study.

There's "estimated potential for up to 100-fold increase in Delta neutralization post-dose three compared to pre-dose three," researchers wrote in the Pfizer data slides.

The data, which haven't yet been peer reviewed or published, also show that antibody levels are much higher after a third dose than a second dose against the original coronavirus variant and the Beta variant, first identified in South Africa.

The Centers for Disease Control and Prevention hasn't yet recommended booster shots, despite the Delta variant creating another wave of infections nationwide.

But two Duke University physicians said they expect that guidance to change sooner rather than later.

"The question of when to boost and what to boost with is still an open question," said Dr. David Montefiori, of the Duke Human Vaccine Institute. “If there is an increase in breakthrough infections that lead to more severe disease, that is going to be the trigger to say, now is the time to start boosting people."

"Breakthrough" infections are cases in which fully vaccinated people contract the virus.

A booster shot would likely strengthen the immune response to all of the virus' variants, including Delta, Montefiori said. Studies are underway to determine if people can use any of the approved vaccines as a booster, or whether they need to get another shot of the same vaccine they received previously.

"I think it will be possible to have options available to you when it comes time to be boosted," he said.

Even without a booster, vaccinations are limiting severe cases of COVID-19, said Dr. Cameron Wolfe, with Duke's School of Medicine.

“It is more infectious. You get sicker a little quicker," Wolfe said of the Delta variant. "For the vaccinated, this has been a very mild illness.”

Jennifer Fabius has had her shot, but she also has her concerns.

"I definitely don’t feel the relief I did in May,” Fabius said, adding that she worries Delta won't be the last variant to pose problems.

"[The virus could] keep mutating to the point we don’t really have the protection from the vaccine anymore," she said.

Montefiori agrees that's a possibility if vaccination rates don't pick up enough for society to reach a herd immunity level that would halt the spread of the virus.

"Unless we can shut this pandemic down, it is possible this virus will continue to become more contagious and even more of a problem," he said. "The Delta variant is still very susceptible to those neutralizing anti-bodies. It has not evolved yet to the point it is escaping our vaccines to a substantial degree."

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