Two new sub-lineages of the Omicron variant of the coronavirus have been spotted in South Africa, the head of gene-sequencing in the country said on Twitter. The lineages have been named BA.4 and BA.5, and while they are accounting for an increasing proportion of cases in South Africa they have not caused a spike in overall numbers. Omicron, and its sub-lineages, have proved to be extraordinarily transmissible, but much less likely to cause hospitalization and death in those infected than earlier variants such as Delta. The new sub-lineages have also been found in samples from Botswana, Belgium, Germany, Denmark and the U.K., suggesting they will soon be spotted all over the world.