Omicron could ‘push Delta out’ by boosting immunity against it, study suggests

People previously infected by Omicron variant developed more immunity to Delta, potentially reducing its ability to reinfect, South African research finds

There could be wider implications for the pandemic if Omicron displaces Delta, but experts warn further evidence is needed that the former causes milder illness

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Early signs have suggested Omicron causes a milder illness. Photo: AFP

Published: 6:00am, 29 Dec 2021

New findings from South Africa suggest that the Omicron coronavirus variant could muscle out its highly transmissible predecessor Delta for good, according to researchers studying how the body’s immune system responds to the two variants.

Their data, released by the researchers on Monday in a paper that has not been peer-reviewed, indicated that previous infection with the Omicron variant enhances immune protection against the Delta variant, potentially reducing Delta’s ability to reinfect people after Omicron infection.

This suggests that the rapidly spreading Omicron – already identified in more than 110 countries – could displace the previously dominant Delta, the researchers said, on the basis that Delta could have little room to spread in an Omicron-dominant area.

That displacement, they argued, could in turn have implications for the trajectory of the pandemic itself, if early signs that Omicron causes more mild illness are confirmed.

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“Along with emerging data indicating that Omicron, at this time in the pandemic, is less pathogenic than Delta, such an outcome may have positive implications in terms of decreasing the Covid-19 burden of severe disease,” wrote lead author Alex Sigal, of the Africa Health Research Institute in Durban, and his colleagues, who have been at the forefront of research on Omicron since it was first reported in November.

The latest results are based on a small-scale laboratory study involving blood samples from 13 participants, both vaccinated and unvaccinated, who were at the time infected with the Omicron variant. Their antibody levels against the two strains were measured first when they were enrolled soon after the onset of symptoms, and again at a median of 14 days after enrolment.