WHO reports new Omicron subvariant cases detected in 29 countries worldwide

A new COVID-19 subvariant, XBB.1.5, is causing concern in the US, where it has been spreading rapidly since December.

Data from the US Centers for Disease Control and Prevention (CDC) has estimated that XBB and XBB.1.5 accounted for 44.1% of US COVID-19 cases in the week of 31 December, compared to 25.9% in the previous week. XBB.1.5 has also been detected in 29 other countries worldwide, the World Health Organization (WHO) reported.

XBB.1.5, which is another descendant of the Omicron variant, is “the most transmissible subvariant that has been detected yet”, WHO COVID-19 technical lead, Maria Van Kerkhove, said at a press conference this week.

The reason for this is because of the mutations XBB.1.5 contains, allowing it to adhere to cells and replicate easily.

"We are concerned about its growth advantage, in particular in some countries in Europe and in the US, particularly the northeast part of the US where XBB.1.5 has rapidly replaced other circulating variants," Van Kerkhove said.

WHO said it does not yet have any data on the severity of XBB.1.5, but currently has no indication that this would have increased. “That is something that we are watching closely through experimental studies in the lab and in real world data,” Van Kerkhove said. “Our concern is how transmissible it is.”

Those who have had COVID-19 before are still susceptible to infection, but vaccines are helping to protect against serious illness. As with other variants of the virus, the risk of becoming seriously ill remains highest for people who are elderly or who have significant underlying health conditions.

WHO’S Technical Advisory Group on Virus Evolution (TAG-VE), which meets regularly to review the latest scientific evidence on circulating SARS-CoV-2 variants and advises WHO on whether a change in public health strategies is warranted, is currently evaluating the rapidly increasing proportion of XBB.1.5 in the US and other countries.

The CDC previously said it was keeping ‘a close eye’ on the XBB variant in November, when it announced that the two new Omicron subvariants, BQ.1 and BQ.1.1, accounted for over 44% of US COVID-19 cases for the week ending 12 November.