WHO has added the BA4 and BA5 sub-strains to its watch list.
The World Health Organization (WHO) tracks dozens of infections with two new highly contagious omicron sub-strains of the coronavirus to assess whether they are more infectious or dangerous.
On Monday, the WHO said it had added the PA4 and PA5 sub-strains of the original Omicron PA1 strain to its watch list. It is already tracing the PA1 and PA2 strains now circulating the world and PA1.1 and PA3 strains.
The organization stated that it had begun tracing them because of "the additional mutations that need to be studied further to understand their effects on the possibility of overcoming immunity."
Viruses mutate all the time, but only some mutations affect their ability to spread or overcome immunity acquired from vaccination, previous infection, or the severity of the disease they cause.
For example, the PA2 strain currently accounts for nearly 94 percent of all sequential cases. It is more likely to spread than other Omicron subspecies. Still, the evidence indicates that it is not expected to cause severe disease.
The World Health Organization says that only a few dozen infections with the two strains (PA4) and (PA5) have been detected in the global database (Global Initiative for the Exchange of All Influenza Data).
Last week, Britain's Health Security Agency said that the BA4 sub-strain had been detected in South Africa, Denmark, Botswana, Scotland, and England from January 10 to March 30.