How much should people worry about Covid’s newly-dominant XBB.1.5 variant? Our medical analyst explains

A new Covid-19 variant, XBB.1.5, is spreading rapidly throughout the United States. In December 2022, the proportion of new Covid-19 infections due to this Omicron offshoot have increased from 4% to 18%, according to a January 6 release from the US Centers for Disease Control and Prevention, and is projected to rise further still. In some parts of the country, it constitutes more than half of all new infections. According to the World Health Organization, XBB.1.5 is the most transmissible form of Omicron yet.

What should people know about XBB.1.5? Do vaccines and treatments work against it? Can tests pick it up? Will hospitals become overwhelmed again? Should kids wear masks to school again? And could there be even more worrisome variants that emerge in the future?