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WHO epidemiologist Dr Maria Van Kerkhove has shared an important Twitter thread on the BA.2 sub-variant of Omicron, which is more transmissible than the BA.1 strain.
Based on available data of transmission, severity, reinfection, diagnostics, therapeutics and impacts of vaccines, BA.2 sublineage of Omicron should continue to be considered a variant of concern and should remain classified as Covid-19 Omicron, the global health body said.
WHO further said that reinfection with Covid-19 Omicron BA.2 following infection with BA.1 has been documented. The initial data from population-level reinfection studies suggest that infection with BA.1 provides strong protection against reinfection with BA.2, it added.
WHO will continue to monitor the BA.2 lineage and has requested countries to continue to be vigilant, to monitor and report sequences and to conduct independent and comparative analyses of the different sublineages.
Calling on public health authorities to keep a strict vigil over the variant, the WHO has said, “BA.2 sublineage should continue to be considered a variant of concern and that it should remain classified as Omicron."
How BA.2 differs from BA.1
BA.2 differs from BA.1 in its genetic sequence, including some amino acid differences in the spike protein and other proteins. Several studies have shown that BA.2 has a growth advantage over BA.1.
WHO said studies are underway to understand the reasons for this growth advantage, but initial data suggest that BA.2 appears to spread faster than BA.1, which currently remains the most common Omicron sublineage reported.
However, this difference in transmissibility appears to be much smaller than the difference between BA.1 and Delta.
Since first being detected in South Africa in late November 2021, Omicron has travelled across the globe, precipitated a massive rise in cases and replaced Delta to become the dominant strain. This spike in Covid infections due to Omicron is now in abeyance.
At the same time, the BA.2 sub-variant is becoming dominant in Denmark, increasing in the UK and also cropping up elsewhere, including India and Pakistan.
“At a global level, the proportion of reported sequences designated BA.2 has been increasing relative to BA.1 in recent weeks, however the global circulation of all variants is reportedly declining," the UN health agency said.
Meanwhile, a Danish study said that reinfection with the BA.2 subtype of the Omicron variant of coronavirus can occur shortly after initial infection with the BA.1 strain.
With the surge of Omicron subvariants BA.1 and BA.2, a large number of reinfections from earlier cases have been observed, the researchers said.
This has raised questions of whether BA.2 specifically can escape the natural immunity acquired shortly after a BA.1 infection, they said.
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