The Omicron variant of coronavirus may reduce the incidence of severe COVID-19 disease, and the infection may become less disruptive to individuals and society in future, according to a study conducted by researchers in South Africa.

The findings of the yet-to-be peer-reviewed study are consistent with the previous observations of Omicron displacing Delta since the variant can elicit immunity which neutralises Delta. The researchers from Africa Health Research Institute observed in samples from 23 people infected with Omicron in November and December that the variant escapes neutralising immunity elicited by Delta infection. This indicates that Omicron can re-infect Delta infected individuals but not vice-versa, giving Omicron an advantage over Delta, they 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," the authors of the study noted.

The finding is an update to the study by the same research team which found enhancement of immunity against Delta variant with Omicron infection. "We were able to add study participants to see more clearly the effect of vaccination," Professor Alex Sigal, from Africa Health Research Institute tweeted on 18 January.

The earlier part of the study, posted on the pre-print repository MedRxiv, used data from 15 previously vaccinated and unvaccinated people who were infected with the Omicron variant. The scientists used plasma, a blood product that contains antibodies, from the participants to test the ability of the antibodies to control both Omicron and Delta in the lab -- a so-called 'neutralisation' test.

The results show a developing antibody response to Omicron, with neutralisation increasing 14-fold over this time. However, the team also observed that the participants developed some enhanced immunity against the Delta variant, with Delta neutralisation increasing 4.4-fold.

The study also showed that vaccinated participants were able to mount a better neutralising response against Delta, while the response in unvaccinated participants was more variable. "Hopefully, all this means Delta is on its way out as Omicron may shut the door on Delta re-infections. Provided enough people vaccinate. The unvaccinated lose out on the extra Omicron protection and don't gain a boost to Delta," said Sigal.

The Omicron variant of SARS-CoV-2, the virus which causes COVID-19, was first identified in November last year in South Africa and Botswana. The variant has been shown to be highly transmissible and have extensive evasion of neutralising antibody immunity elicited by vaccination and previous SARS-CoV-2 infection.