The current wave of Covid-19 highlights a high risk of reinfection by the Omicron variant of SARS-CoV-2. Why is this? Researchers analysed the antibody neutralisation capacity of 120 people infected with the original SARS-CoV-2 strain, or with the Alpha, Beta, Gamma, Delta, Zeta or Omicron (sub-variant BA.1) variants. They found that unlike its predecessors, Omicron appears able to evade the antibodies generated by all other variants, the University of Geneva said in a press release.
The researchers, from the University’s Centre for Emerging Viral Diseases, and the Geneva University Hospital, have published their findings in Nature Communications.
In vaccinated individuals, while the neutralisation capacity is also reduced, it remains far superior to natural immunity alone. This could explain why Omicron is responsible for a net increase in vaccine breakthrough infections, but not in hospitalisations, the release said.
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 aim was to determine how well the antibodies generated during the first infection were able to neutralise the different variants of SARS-CoV-2. “Omicron proved to be the most effective at evading pre-existing natural immunity, as well as, to a lesser extent, that induced by vaccination,” the release quoted researcher Benjamin Meyer as saying. Indeed, antibody levels against ancestral SARS-CoV-2 in vaccinated people are roughly 10 times higher than in people who have only developed post-infection immunity. Moreover, the combination of the two, known as hybrid immunity, seems to maintain even higher and broader reactive antibody levels.
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Thus, Omicron can evade existing immunity and cause an infection, but hospitalisation and death due to Covid-19, even with Omicron, is still reduced after vaccination, the release said.“ Nevertheless, SARS-CoV-2 retains an astonishing ability to mutate… Vigilance is still required, especially as the epidemiological curves have been rising sharply since the appearance of BA.5,” it quoted researcher Isabella Eckerle as saying.
(Source: University of Geneva)