A new research on Omicron-infected patients suggests that the current COVID wave, driven by the new strain, appears to cause less severe illness and even provide protection against the deadlier Delta variant.

South Africa-based researchers found that those who previously caught the Delta variant could contract Omicron, while those who get the Omicron strain couldn't be infected with Delta, particularly if they have been vaccinated. "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 Alex Sigal of the Africa Health Research Institute.

"We have an update to our study which found enhancement of Delta immunity with #Omicron infection," he posted in a tweet. Yet to be peer-reviewed, the updated study used samples from 23 people who were infected with Omicron strain in November and December in South Africa.

The researchers, led by Sigal, investigated whether neutralising immunity elicited by Omicron infection would also neutralise the Delta variant and the role of prior vaccination. Some participants were unvaccinated while others were breakthrough cases vaccinated with Pfizer or Johnson and Johnson vaccines.

In vaccinated participants, neutralisation of Omicron increased 13.7-fold over baseline. This compared to a 4.4-fold increase in unvaccinated individuals. Over the same period, Delta virus neutralisation was enhanced 6.6-fold in vaccinated but only 2.5-fold in unvaccinated participants.

"Moreover, vaccinated participants were able to mount a stronger neutralisation response against Delta relative to Omicron virus. This was not the case in unvaccinated individuals, some of whom continued to show low Delta neutralisation," the researchers wrote. According to the study, higher Omicron neutralisation in vaccinated individuals may enable a more effective immune response to Omicron, while enhancement of Delta neutralisation should lead to lower Delta re-infections.

"Given emerging data indicating Omicron is less pathogenic than Delta, such an outcome may have implications in terms of decreasing COVID-19 severe disease," the researchers noted. Citing this study, World Health Organization (WHO) Chief Scientist Soumya Swaminathan said Omicron gave protection against Delta in people who were vaccinated.

"Omicron infection after vaccination increases immunity against #Delta also. But in unvaccinated people, it doesn't generate immunity against other variants. So, infection is not a substitute for vaccination, as some are suggesting," she tweeted. These results are consistent with Omicron displacing the Delta variant since Omicron can elicit immunity which neutralises Delta.

"In contrast, we have observed in this study and others have previously shown that Omicron 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," the researchers argued.

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," they noted.