Omicron sub-variants are showing signs of “increased transmissibility and properties of immune escape”, the World Health Organization has warned, but reduced surveillance has limited efforts to understand the ramifications.
At a press conference Dr Maria Van Kerkhove, the head of the UN agency’s technical team for Covid, said that more than 300 versions of omicron are now circulating globally. These are not causing more severe disease, but they are developing some qualities “of concern”.
“All of these variants of omicron are showing increased transmissibility and properties of immune escape,” she said. “We don’t see a change in severity yet and our vaccines remain effective, but we have to remain vigilant.”
Although no single variant is currently dominant, three are spreading quickly: XBB, which has driven a new wave of infections in Singapore, and BQ.1 and BQ.1.1, which are spreading in Europe and are now responsible for around 11 per cent of cases in the United States.
Available data suggests XBB, which has been spotted in 26 countries, may be the best at evading immunity. In one study by researchers in China, the variant partially evaded antibodies generated by a previous infection with BA.5, an older omicon sub-variant.