‘Natural immunity’ from COVID-19 omicron is weak and limited

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Scientists from Gladstone Institutes and UC San Francisco found that in unvaccinated people, infection with the omicron variant of COVID-19 provides little long-term immunity against other variants.

The research is published in the journal Nature and was conducted by Melanie Ott et al.

As the omicron variant of SARS-CoV-2 spread around the globe in late 2021 and early 2022, evidence quickly mounted that it was causing less severe symptoms than delta and other variants of concern.

However, scientists weren’t initially sure why that was, or how a weaker infection might impact long-term immunity against COVID-19.

In experiments using mice and blood samples from donors who were infected with omicron, the team found that the omicron variant induces only a weak immune response.

In vaccinated people, this response—while weak—helped strengthen overall protection against a variety of COVID-19 strains.

In those without prior vaccination, however, the immune response failed to confer broad, robust protection against other strains.

The team analyzed blood samples from ten unvaccinated people who had been infected with omicron—their blood was not able to neutralize other variants.

When they tested blood from 11 unvaccinated people who had been infected with delta, the samples could neutralize delta and the other variants to a lesser extent.

But vaccinated people with confirmed omicron or delta breakthrough infections all showed the ability to neutralize all the tested variants, conferring higher protection.

These results are useful not only to inform individuals’ decisions on vaccination but also for the design of future COVID-19 vaccines that confer broad protection against many variants

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