The World Health Organization is currently tracking a few dozen cases of two additional subvariants of the highly transmissible Omicron strain of SARS-CoV-2 to determine if they are more infectious or dangerous.
On Monday, the WHO announced that it had added BA.4 and BA.5 to its watch list. The organization already tracks other members of the Omicron family, including BA.1 and BA.2 – the now globally dominant sub-variant – as well as BA.1.1 and BA.3.
The WHO said it started tracking them because of their “additional mutations that need to be further studied to understand their impact on immune evasion potential.”
Viruses mutate all the time, but only certain mutations affect their ability to spread or evade immunity prior to vaccination or infection, or the severity of the disease they cause.
For example, BA.2 now accounts for almost 94% of all sequenced cases and is more transmissible than its siblings, but evidence so far suggests it is not more likely to cause severe disease.
According to the WHO, only a few dozen cases of BA.4 and BA.5 have been reported to the global database GISAID.
BA.4 cases found in several countries
The UK Health Security Agency said last week that BA.4 was found in South Africa, Denmark, Botswana, Scotland and England from January 10 to March 30.
All of the BA.5 cases were in South Africa 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 year olds who were fully vaccinated and suffered from 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 Center for Epidemic Response. & Innovation in South Africa in a Monday article series shared on Twitter.