With an unpremeditated spike in Omicron cases worldwide, often coupled with infections caused by the Delta variant, a study led by an international team of researchers shows that the vaccine-evading newer variant enhances the neutralising immunity of the Delta variant.
The study — carried out by researchers from South Africa, the US and Germany, posted on a pre-print server and is yet to be peer-reviewed — included both previously vaccinated and unvaccinated individuals who were infected with SARS-CoV-2 in the Omicron infection wave in South Africa soon after symptom onset.
The team then measured their ability to neutralise both Omicron and Delta virus at the times of enrollment versus a median of 14 days after enrollment. The findings showed that neutralisation of Omicron increased 14-fold over this time, indicating the development of antibody response to the variant.
Importantly, there was an enhancement of Delta virus neutralisation, which increased 4.4-fold.
"The increase in Delta variant neutralisation in individuals infected with Omicron may result in decreased ability of Delta to re-infect those individuals," said Professor Alex Sigal, a virologist at the Africa Health Research Institute.
"Comparing Omicron and Delta neutralisation showed that vaccinated participants were able to mount a better neutralising response against Delta virus, while the response in unvaccinated participants was more variable," Sigal said.
While emerging data indicates that Omicron, at this time in the pandemic, is less pathogenic than Delta, the study outcome may have positive implications in terms of decreasing the Covid-19 burden of severe disease, he noted.
The Omicron variant of SARS-CoV-2, first identified in November 2021 in South Africa and Botswana, has been shown to have an extensive but incomplete escape from immunity elicited by vaccines and previous infections, with boosted individuals showing effective neutralisation, even though vaccine and booster efficacy may wane over time.
While Omicron infections are rising steeply, many countries still have high levels of infection comprising the Delta variant.
The results of the study are also consistent with Omicron displacing the Delta variant, "since it can elicit immunity which neutralises Delta making re-infection with Delta less likely. In contrast, Omicron escapes neutralising immunity elicited by Delta and therefore may re-infect Delta infected individuals," Sigal said.
"The implications of such displacement would depend on whether Omicron is indeed less pathogenic than Delta. If so, then the incidence of Covid-19 severe disease would be reduced and the infection may shift to become less disruptive to individuals and society," Sigal noted.
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