BA.4 found so far in South Africa, Denmark, Botswana and parts of the U.K.
The World Health Organization is now tracking a few dozen cases of two additional sub-variants of the highly transmissible Omicron strain of SARS-CoV-2 to assess whether they're more infectious or dangerous.
On Monday, the WHO announced it has added BA.4 and BA.5 to its list for monitoring. The organization is already tracking other members of the Omicron family, including BA.1 and BA.2 — the sub-variant now globally dominant — as well as BA.1.1 and BA.3.
The WHO said it had begun tracking them because of their "additional mutations that need to be further studied to understand their impact on immune escape potential."
Viruses mutate all the time but only some mutations affect their ability to spread or evade prior immunity from vaccination or infection, or the severity of disease they cause.
For instance, BA.2 now represents nearly 94 per cent of all sequenced cases and is more transmissible than its siblings, but the evidence so far suggests it is no more likely to cause severe disease.
Only a few dozen cases of BA.4 and BA.5 have been reported to the global GISAID database, according to the WHO.
BA.4 cases found in multiple countries
The UK's Health Security Agency said last week BA.4 had been found in South Africa, Denmark, Botswana, Scotland and England from Jan. 10 to March 30.
All the BA.5 cases were in South Africa as of last week, but on Monday Botswana's health ministry said it had identified four cases of BA.4 and BA.5, all among people aged 30 to 50 who were fully vaccinated and experiencing mild symptoms.
Despite the increase in the percentage of genomes, BA.4 and BA.5 are not yet causing a spike in infections in South Africa, and further evolution of the Omicron variant was expected, said Tulio de Oliveira, director of the Centre for Epidemic Response & Innovation in South Africa in a Monday series of posts shared on Twitter.
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