Immunity in unvaccinated people after catching Omicron offers little long-term protection against other variants, a new study has found.
Scientists found that the variant creates a weak immune response in vaccinated people that strengthens overall protection from a variety of other Covid strains.
However, unvaccinated individuals do not receive 'broad, robust' protection from other variants after having Omicron.
An infection with Omicron is roughly equivalent to one shot of a vaccine, reported researchers from Gladstone Institutes and UC San Francisco (UCSF).
"This research underscores the importance of staying current with your vaccinations, even if you have previously been infected with the Omicron variant, as you are still likely vulnerable to re-infection," said co-senior author Jennifer Doudna, PhD.
The researchers explained how when Omicron emerged, people wondered if the strain - which had less severe symptoms than Delta - could essentially act as a vaccine for people who didn't want to get vaccinated.
Their findings show that unvaccinated people ended up with very little protection from other variants.
"When it comes to other variants that might evolve in the future, we can't predict exactly what would happen, but based on these results, I'd suspect that unvaccinated people who were infected with Omicron will have very little protection," said Melanie Ott, MD, PhD, director of the Gladstone Institute of Virology and co-senior author of the new work.
"But on the contrary, vaccinated individuals are likely to be more broadly protected against future variants, especially if they had a breakthrough infection."
Charles Chiu, MD, PhD, a UCSF infectious diseases professor and co-senior author, said: "Our results may be 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."
To determine how much immunity Omicron lent, the team of researchers studied Omicron in mice and blood samples from people who had the strain.
They gauged how the immune response against Omicron fared over time by collecting blood samples from mice infected with the ancestral, Delta, or Omicron variants.
Scientists measured the ability of their immune cells and antibodies to recognise five different viral variants - ancestral, Alpha, Beta, Delta, and Omicron.
Blood from uninfected animals was unable to neutralise any of the viruses - in other words, block the ability of any of the viruses to copy themselves.
They found blood from Omicron-infected mice could only neutralise the Omicron variant.
The team confirmed these results using blood from ten unvaccinated people who had been infected with Omicron. 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.
Then when they repeated the experiments with blood from vaccinated people, the results were different: vaccinated individuals with confirmed Omicron or Delta breakthrough infections all showed the ability to neutralise all the tested variants, conferring higher protection.
The findings were published in the journal Nature .
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