Research by South African scientists suggests that Omicron infection enhances neutralizing immunity against the Delta variant of the coronavirus.

The study, which has not been peer-reviewed, found that people who were infected with Omicron, especially those who were vaccinated, developed enhanced immunity to the Delta variant.

The analysis enrolled 33 vaccinated and unvaccinated people who were infected with the Omicron variant in South Africa.

While the authors found that the neutralization of Omicron increased 14-fold over 14 days after the enrollment, they also found that there was a 4.4 fold increase of Delta virus neutralization.

"The increase in Delta variant neutralization in individuals infected with Omicron may result in decreased ability of Delta to re-infect those individuals," the scientists said.

Alex Sigal, a professor at the Africa Health Research Institute in South Africa, said on Twitter on Monday that if Omicron was less pathogenic as it looked from the South African experience, "this will help push Delta out".

According to an earlier South African study, there is reduced risk of hospitalisation and severe disease in people infected with the Omicron coronavirus variant compared with the Delta one, though the authors say some of that is likely due to high population immunity.

The Omicron variant, first detected in southern Africa and Hong Kong in November, has since spread worldwide and threatened to overwhelm hospitals and disrupt travel plans this holiday week.