Omicron infection immunity?

WITHOUT vaccination, an infection with omicron fails to confer robust immunity against other Covid-19 variants, finds a study.

In experiments using mice and blood samples from donors who were infected with omicron, researchers at Gladstone Institutes and UC San Francisco (UCSF) in the US, found that the omicron variant induces only a weak immune response.

In vaccinated individuals, the response, while weak, helped strengthen overall protection against a variety of Covid strains. In those without prior vaccination, however, the immune response failed to confer broad, robust protection against other strains, revealed the study published in the journal Nature.

In the unvaccinated population, an infection with omicron might be roughly equivalent to getting one shot of a vaccine,” said Melanie Ott, the director of the Gladstone Institute of Virology. “It confers a little bit of protection against Covid-19, but it’s not very broad,” Ott added.

The team of researchers found that despite the milder symptoms, the immune system in mice infected with omicron generated the T cells and antibodies typically seen in response to other viruses.

In order to gauge how the immune response against omicron fared over time, the researchers collected blood samples from mice infected with the ancestral delta or omicron variants of Sars-CoV-2. They then measured the ability of their immune cells and antibodies to recognise five viral variants – ancestral (WA1), alpha, beta, delta and omicron.

Blood from uninfected animals was unable to neutralise any of the viruses. Samples from WA1-infected animals could neutralise alpha and, to a lesser degree, the beta and delta virus but not omicron. Samples from delta-infected mice could neutralise delta, alpha and, to a lesser degree, the omicron and beta virus.

However, blood from omicron-infected mice could only neutralise the omicron variant. The team confirmed the results using blood from 10 unvaccinated people who had been infected with omicron, that their blood was not able to neutralise other variants. When they tested blood from 11 unvaccinated people who had been infected with delta, the samples could neutralise delta and, as had been seen in mice, the other variants to a lesser extent.