On Monday, the WHO announced that it had added BA.4 and BA.5 to its watch list. The organization is already monitoring other members of the Omicron family, including BA.1 and BA.2 – the most prevalent sub-variant worldwide – as well as BA.1.1 and BA.3. The WHO said it had begun monitoring them because of “additional mutations that need to be studied further to understand their impact on the immune system’s escape potential”. Viruses are constantly mutating, but only certain mutations affect their ability to spread or prevent previous immunity from vaccination or infection or the severity of the disease they cause. For example, BA.2 now accounts for almost 94 percent of all sequence cases and is more contagious than its siblings, but evidence to date suggests it is less likely to cause serious illness. Only a few dozen cases of BA.4 and BA.5 have been reported in the global GISAID database, according to the WHO.
BA.4 cases found in many countries
The UK Health and Safety Administration said last week that BA.4 had been found in South Africa, Denmark, Botswana, Scotland and England from January 10 to March 30. All BA.5 cases have been in South Africa since last week, but on Monday the Botswana Ministry of Health said it had identified four cases of BA.4 and BA.5, all between 30 and 50-year-olds who had been fully vaccinated and showed mild symptoms. Despite the increase in the genome rate, BA.4 and BA.5 are not yet causing an increase in infections in South Africa and further evolution of the Omicron variant was expected, said Tulio de Oliveira, director of the South Africa Epidemic & Innovation Center in a series of Monday posts posted on Twitter.
