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How Omicron Evades Antibodies in Vaccinated and Unvaccinated People

The current wave of Covid-19 highlights a high risk of re-infection with the Omicron variant of SARS-CoV-2. Why is it? The researchers analyzed the neutralizing ability of antibodies from 120 people infected with the original SARS-CoV-2 strain, or the Alpha, Beta, Gamma, Delta, Zeta or Omicron (BA.1 subvariant) variants. They found that unlike its predecessors, Omicron appears to be able to evade antibodies generated by all other variants, the University of Geneva said in a press release.

The researchers, from the University Center for Emerging Viral Diseases and the University Hospital of Geneva, published their findings in Nature Communications.

In vaccinated individuals, if the capacity for neutralization is also reduced, it remains much higher than natural immunity alone. This could explain why Omicron is responsible for a sharp increase in vaccine-related infections, but not hospitalizations, according to the statement.

The research team took blood samples from 120 volunteers previously infected with one of the different variants, unvaccinated, or vaccinated and infected, either before or after vaccination.

The objective was to determine to what extent the antibodies generated during the first infection were able to neutralize the different variants of SARS-CoV-2. “Omicron was found to be most effective in evading pre-existing natural immunity, as well as, to a lesser extent, that induced by vaccination,” the statement quoted researcher Benjamin Meyer as saying. Indeed, antibody levels against ancestral SARS-CoV-2 in vaccinated people are about 10 times higher than in people who have only developed post-infection immunity. Moreover, the combination of the two, known as hybrid immunity, appears to maintain even higher and broader levels of reactive antibodies.

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Thus, Omicron may evade existing immunity and cause infection, but hospitalizations and deaths from Covid-19, even with Omicron, are still reduced after vaccination, the statement said. “Nevertheless, SARS-CoV-2 retains an astonishing ability to mutate… Vigilance is always in order, especially since the epidemiological curves have risen sharply since the appearance of BA.5,” said researcher Isabella Eckerle.

(Source: University of Geneva)

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