New research shows infection with the SARS-CoV-2 Omicron variant creates a neutralising immune response against the Delta variant.

The work, led by Africa Health Research Institute’s Professor Alex Sigal, has been submitted as a preprint to medRxiv and is available here.

The research team enrolled 15 previously vaccinated and unvaccinated people who were infected with the Omicron variant into the study. They used plasma, a blood product which 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. They measured this close to when the participants had symptoms, and again around two weeks later.

As expected, 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 researchers also show that vaccinated participants were able to mount a better neutralising response against Delta, while the response in unvaccinated participants was more variable.

“The increase in Delta variant neutralisation in individuals infected with Omicron may result in decreased ability of Delta to re-infect those individuals,” said Prof Sigal. “If Omicron does prove to be less pathogenic, then this may show that the course of the pandemic has shifted – Omicron will take over, at least for now, and we may have less disruption of our lives.”

Top image: Enhancement of Delta neutralization by Omicron infection. (A) Omicron (A) or Delta (B) virus neutralisation by blood plasma from n=13 participants infected in the Omicron infection wave at enrollment (median 4 days post-symptom onset) and at follow-up (median 14 days post-enrollment).