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Pfizer-BioNTech Covid-19 vaccines at a senior living facility in Worcester, Pa., on Aug. 25, 2021.
Pfizer-BioNTech Covid-19 vaccines at a senior living facility in Worcester, Pa., on Aug. 25, 2021. (Hannah Beier/Bloomberg)

The omicron variant dented the protection afforded by two doses of Pfizer's and AstraZeneca's COVID vaccines as feared, researchers found, increasing the risk of infection.

Blood samples collected from people vaccinated with the two different shots and tested against the new strain showed a substantial drop in neutralizing antibodies, a proxy for protection, particularly compared with the delta variant, researchers from the University of Oxford said Monday in a paper.

The results echo other recent findings that emphasize the need for booster shots, especially amid evidence of omicron's ability to drive a tidal wave of infections. The scientists couldn't yet answer another key question, about the vaccines' ability to ward off severe disease. The new mutation has sparked concern around the globe, but reports from South Africa — where it was first discovered — suggest so far cases appear to be milder than during earlier surges.

Omicron's impact should become better documented in a few more weeks, making clear whether new vaccines are needed, according to Teresa Lambe, one of the creators of the shot that Astra developed with Oxford.

"We're hopeful that the current vaccine will protect against severe disease and hospitalization and that's certainly what we've seen before with other variants of concern," Lambe told reporters. "We and other vaccine manufacturers are in a position that if a new variant vaccine is needed, we can go fast."

In the meantime, the rise in infections alone could strain hospitals in places like the U.K. Gavin Screaton, head of Oxford's medical-sciences division and lead author of the paper, called for remaining "cautious, as greater case numbers will still place a considerable burden on health-care systems."

The researchers saw a roughly 30-fold drop in neutralizing antibodies against omicron after two doses of the Pfizer vaccine compared with the delta strain. The impact on the Astra shot was similar. The authors also found evidence of some participants failing to neutralize the virus at all.

Neutralizing antibodies are just one arm of the immune system's defense, and the scientists are now looking at how T cells respond to the variant, with data expected in the coming weeks.

The blood samples were taken from the Oxford-led Com-Cov2 study looking at how mixing and matching vaccines with different intervals impacts the immune response to COVID-19. The findings on omicron were mainly based on those volunteers that had two shots of the same vaccine, the researchers said at a press briefing Monday.

The data was published on the pre-print server medRxiv and has been submitted for peer review.


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