LONDON—The U.K. is emerging as a testing ground in the battle for dominance between the new Omicron variant of the coronavirus and Delta, the earlier strain that is currently driving most infections in the U.S. and Europe.
How Britain fares against Omicron will offer clues to the U.S. and the rest of the industrialized world about how the variant behaves in a highly vaccinated population, how sick those who are infected get and if its dozens of mutations have given Omicron enough of an advantage on the evolutionary ladder to starve Delta of the hosts it needs to stay on top.
