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Study finds Pfizer vaccine boosts, not destroys, immunity from past COVID-19 infection

September 15, 2022 GMT

CLAIM: A study published in the New England Journal of Medicine found that the effectiveness of Pfizer’s COVID-19 vaccine becomes “negative” within five months and destroys immunity garnered from prior infection with COVID-19.

AP’S ASSESSMENT: False. While the study found that the vaccine’s efficacy in children decreased over time, the study also determined that vaccination actually boosted the immunity of children who had previously been infected with COVID-19, compared to those who had only been infected, the lead author of the study told The Associated Press.

THE FACTS: A blog post claiming that the Pfizer COVID-19 damages immunity acquired from prior infection has spread widely across social media platforms over the past week.

The blog post, titled, “Covid Vaccine Destroys Natural Immunity, NEJM Study Shows,” was shared widely on Twitter, Facebook, Reddit, and Instagram. The post states that the study “shows not only that the effectiveness of the Pfizer Covid vaccine becomes negative (meaning the vaccinated are more likely to be infected than the unvaccinated) within five months but that the vaccine destroys any protection a person has from natural immunity.” One tweet promoting the blog post was shared more than 10,000 times.

But the post misrepresents the study’s findings, according to the study’s lead author, Danyu Lin, a biostatistics professor at the University of North Carolina at Chapel Hill.

“The evidence we have supports the finding that natural immunity is boosted by vaccination rather than being destroyed by vaccination as claimed,” Lin said.

The study analyzed vaccination histories and clinical outcomes of children aged 5 to 11 between Nov. 1, 2021, and June 3, 2022 — when the omicron variant was on the rise — to assess the protection offered by the Pfizer COVID-19 vaccine. The analysis also incorporated data on infections among children in that age group dating back to March 2020, to scrutinize the protection offered by prior infection.

The study, which has been peer-reviewed and was published Sept. 7 in the New England Journal of Medicine, found that while two doses of the Pfizer vaccine were protective, the protection they offered decreased over time. Immunity from prior COVID-19 infection also diminished over time, though the vaccine proved more effective among children who had previously been infected than those who had not been infected.

“Both the BNT162b2 vaccine and previous infection were found to confer considerable immunity against omicron infection and protection against hospitalization and death,” the study states. “The rapid decline in protection against omicron infection that was conferred by vaccination and previous infection provides support for booster vaccination.”

The blog post misrepresents diagrams published as part of the study, Lin told the AP. For example, one diagram shows a steep drop-off in the protection offered by prior infection with the Delta variant against reinfection among vaccinated children. That chart was cited in the blog post as evidence that immunity from prior infection is eliminated over time following vaccination. But the analysis lacked sufficient data after three months to reliably estimate what came after the apparent reduction, Lin said.

“The effectiveness of prior infection with omicron against reinfection with omicron is actually higher among children who are vaccinated than among the children who are unvaccinated,” he added. “The conclusion is completely opposite to what they claim in their article.”

Lin added that while two other diagrams show the vaccine’s effectiveness going negative over time, that portion of the curve is highly uncertain and unreliable, as the study lacked sufficient data. The study did not determine that the vaccine itself makes children more susceptible to COVID-19, only that its protection waned over time.

He described the claim that the vaccines are destroying people’s natural immunity as “really misleading.”

The blog post “completely misrepresents” what the study shows, said Dr. Otto Yang, a professor of medicine, microbiology, immunology and molecular genetics at the University of California, Los Angeles.

“These are models, statistical models, and so these lines have been extended further than they are supposed to be and extended beyond where the data goes,” Yang said. “If you look at the actual numbers that are reported in the paper, you can see that the vaccines continue to protect kids from being hospitalized or dying. And that’s the bottom line.”

In a statement provided to the AP, Kit Longley, a spokesperson for Pfizer, said that the study’s findings support the efficacy of vaccination.

“Real-world evidence and recent findings, such as those published by The New England Journal of Medicine, reinforce the urgent need for updated vaccines targeted to the Omicron sublineages, including the newly authorized bivalent boosters,” he wrote.

“The NEJM study says two important things—neither of which are that the vaccines somehow don’t work or backfire,” Jeremy Faust, an emergency physician at Brigham and Women’s Hospital and an instructor at Harvard Medical School, wrote in an email to the AP. “First, the study shows that prior infection is indeed protective against hospitalization in future infections.”

“However, children with prior infections should indeed still be vaccinated because; Second, even with the protection that a prior infection offers, the vaccines were shown to still add benefit,” he added.


This is part of AP’s effort to address widely shared misinformation, including work with outside companies and organizations to add factual context to misleading content that is circulating online. Learn more about fact-checking at AP.