You Are Unlikely to Catch Omicron Variant if You Had Omicron

You Are Unlikely to Catch Omicron Variant if You Had Omicron

Finally some good news for the pandemic-weary: a study shows that previous infection with the widely circulating Omicron varian BA.1 version provides strong protection against its relative BA.2, which is growing in prevalence. The results suggest that BA.2 is unlikely to cause a major wave of infections in communities that have experienced a BA.1 wave.

“When I read it, I said, ‘This is definitely reassuring,’” says Eric Topol, a genomicist at Scripps Research in La Jolla, California. The study, which was published on the preprint server medRxiv, has not yet been peer reviewed.

According to World Health Organization (WHO), currently designated COVID variants of concern are:

The two strains diverged around a year ago — months before scientists identified them — and they have since accumulated substantial genetic differences, leading scientists to wonder whether BA.1 infection would provide protection against BA.2. Earlier this month, researchers found that the Omicron variant BA.2 spreads more quickly than BA.1 variant. It also causes more severe disease in hamsters — a common model for studying respiratory illnesses — than does the BA.1 subvariant2, raising concerns that it would cause another spike in cases.

To investigate such worries, Troels Lillebaek, a molecular epidemiologist at the State Serum Institute in Copenhagen, and his colleagues plunged into Denmark’s extensive medical registries. Close to two million Danish residents tested positive for COVID-19 from late November to mid-February, but only 1,739 people had results classed as a reinfection: two positive tests separated by 20–60 days.

The researchers sequenced viral samples from 263 of these people and found that only 47 had contracted BA.2 after an infection with BA.1. By contrast, 140 people had contracted BA.2 after infection with the Delta variant.

Battle of Omicron variants

Omicron variant BA.2 has been proliferating in Denmark since the start of this year, and currently comprises about 88% of all coronavirus cases. But Lillebaek says the wave of BA.1 variant that preceded BA.2 variant is offering protection. “There’s a build-up of immunity at the moment that is preventing a disaster,” he says.

Sarah Otto, an evolutionary biologist at the University of British Columbia in Vancouver, Canada, says these findings are consistent with other recent studies. For example, two laboratory studies (study 1, study 2) have shown that antibodies against BA.1 can protect cells from infection with BA.2, and a UK survey of reinfections in early February did not identify any cases in which a BA.2 infection followed a BA.1 infection. “If BA.2 arrives in a community late, when the BA.1 Omicron wave is nearly over, immunity by Omicron infection and/or by boosting is likely to keep BA.2 from driving a second Omicron wave,” Otto says.

Hope for spare

Topol says the study’s results mean that many communities can relax. “Instead of thinking that [BA.2] is the new bad variant, I think we can put that aside. I see it as not a worry,” he says.

Lillebaek says the study provided one extra piece of good news: it supports the idea that vaccines provide protection against Omicron, including BA.2. “It’s predominantly young, unvaccinated persons where we see this reinfection with BA.2. It kind of indicates that vaccination does give you some protection,” he says.