The World Health Organization says there is so far no epidemiological evidence that coronavirus Omicron subvariants BQ.1 and XBB will be of substantially greater risk than other Omicron sub-lineages.

A WHO advisory group of experts issued a statement on BQ.1 and XBB, which have been detected in some countries, including Japan.

The group says BQ.1 is showing a significant growth advantage over other circulating Omicron sub-lineages in many settings, including Europe and the US.

The experts add that while there are no data from studies with humans, the subvariant may have an immune escape advantage over other circulating Omicron sub-lineages.

They say further investigation is needed to determine whether there is a higher reinfection risk and reduced protection by vaccines.

The advisory group also says available data from some countries, including Singapore, suggest the growth advantage of XBB.

But the experts add that the current data do not indicate there are substantial differences in disease severity for XBB infections.

The WHO says it will continue to closely monitor the two subvariants and is asking countries to be vigilant.