The omicron coronavirus sub-variant known as BA.2 has been found across Africa and countries should sequence more coronavirus samples so the extent of its spread can be determined, the World Health Organization said. 

So far, the strain has been found in Senegal in West Africa, Kenya in East Africa and Malawi, Botswana and South Africa in southern Africa, Nicksy Gumede-Moeletsi, a virologist with the WHO, said Thursday on a conference call.

“We’re a bit concerned that we may have missed some of this BA.2 in some of the samples that we’ve screened previously,” she said. 

BA.2 is worrying scientists as studies show that it appears to be more transmissible than the original omicron strain, the discovery of which was announced by South Africa and Botswana in November. 

Research also shows that getting a mild infection with either of the two strains may not give a robust-enough immune response to protect against another omicron infection. Early data from BA.2 infections in Denmark and the U.K. indicate that the strain doesn’t cause more severe disease.

BA.2 is spreading rapidly in South Africa and has been found in seven of the country’s nine provinces, Tulio de Oliveira, a bio-informatics professor who runs gene-sequencing institutions and advises the government on the pandemic, said in a presentation on Wednesday. It has the potential to cause a second surge of infections in the current wave, he said.