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Simone McCarthy

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Their data, released by the researchers on Monday in a paper that has not been peer-reviewed, indicated that previous infection with the Omicron variant enhances immune protection against the Delta variant, potentially reducing Delta’s ability to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


“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.
The participants’ neutralising immunity against Omicron increased 14-fold during that time, as is expected as the body develops an immune response to an invading virus. However, the researchers also found that participants’ neutralisation of the Delta variant was enhanced, increasing fourfold by the 14-day point.
This signals that Delta could have a decreased ability to reinfect those previously infected with Omicron – a phenomenon not seen in real-life in reverse, with previous infection by Delta seeming not to block reinfection with the rapidly spreading Omicron.
In the latest study, researchers found that vaccinated people had higher levels of immune responses for both variants than unvaccinated participants.
In separate comments on Twitter, Sigal said that the findings suggested Omicron could “help push Delta out”. “If that’s true, then the disruption Covid-19 has caused in our lives may become less,” he wrote.
But experts say it is not yet confirmed that the variant does cause milder disease, and health authorities have stressed that even a milder illness, spreading widely, could overwhelm hospitals.
It is too soon to draw conclusions about Omicron’s illness severity, according to the World Health Organization. Early data from South Africa, Britain and Denmark that suggested a reduced risk of hospitalisation than for Delta was too narrow to give a full picture, the agency said.
Omicron: what we know so far about symptoms, transmissions, vaccines
Its latest technical brief on the variant said it was “still unclear to what extent the observed reduction in risk of hospitalisation can be attributed to immunity from previous infections or vaccination and to what extent Omicron may be less virulent”.
Epidemiologist Ben Cowling, of the University of Hong Kong, said it remained unclear whether the protection against Delta reported in the South African study would be long-lasting, or whether the same observation would be made in other locations which had not experienced large waves of Delta infections.
The South African team also cautioned that participants in their study had probably been infected before Omicron, and more than half were vaccinated – making it unclear whether their results showed specifically Omicron’s ability to neutralise Delta, or “activation of antibody immunity from previous infection and/or vaccination”.
Nonetheless, the results add new data into a question that has followed Omicron as it has spread faster than Delta.


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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



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


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