The coronavirus Omicron strain XBB.1.5, which has become the dominant strain in the U.S. in just a matter of weeks, could drive a new wave of cases, a World Health Organization official told reporters Wednesday.“We are concerned about its growth advantage, in particular in some countries in Europe and the Northeast part of the United States, where XBB.1.5 has rapidly replaced other circulating sub-variants,” said Maria Van Kerkhove, the WHO’s Covid-19 technical lead.What we know: Public health officials have detected the strain in 29 countries, but it could be circulating in many more, Van Kerkhove said.He advised people to get their bivalent booster, to test before attending large gatherings or before meeting with elderly or immunocompromised people and to wear a high-quality mask in crowded indoor spaces.The WHO is working on an analysis of the new strain’s severity that it will publish in the coming days, Van Kerkhove said."