The race is on to track the spread of Omicron

Governments around the world are urgently scouring databases for recent cases of Covid-19 infections, screening travellers and decoding the viral genomes of the new variant as they try to measure how far it has spread.

The pace of the work highlights the pressure on governments and public health authorities to decide quickly whether they need to take unpopular, economically damaging steps to curb Omicron's...