LONDON: Two doses of Pfizer and AstraZeneca's Covid vaccines induced lower levels of antibodies against the Omicron variant, 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 neutralising antibodies, a proxy for protection, researchers from the University of Oxford said on Monday in a paper.
The results echo other recent findings that emphasise 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.
In the meantime, the rise in infections alone could strain hospitals in places like the United Kingdom. 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 neutralising antibodies against Omicron after two doses of the Pfizer vaccine compared with the Delta strain. The impact on the Astra shot was similar.
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.
The data was published on the pre-print server medRxiv. bloomberg
