Discovery of Virus Variant in Colorado and California Alarms Scientists

“I would expect a similar trajectory” in the United States, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle. The variant probably accounts for fewer than 1 percent of cases now, he estimated, but might constitute the majority of cases by March.

The variant has 23 mutations, compared with the original virus discovered in Wuhan, China. Seventeen mutations appeared since the virus diverged from its most recent ancestor, said Muge Cevik, an infectious disease expert at the University of St. Andrews in Scotland and a scientific adviser to the British government.

The speed with which the virus acquired so many alterations worries scientists, who had expected the coronavirus to evolve far more slowly.

Current vaccine candidates should continue to protect people from illness, several experts said. But the appearance of the new variant, which contains at least one mutation that weakens the body’s immune protection, makes it likely that vaccines may need regular adjustment, much as they do to remain effective against the influenza virus.

Scientists are still unsure how much more easily the mutant spreads. Initial estimates were around 70 percent greater transmissibility, but the figure has since been revised to 56 percent and may dip even lower, Dr. Cevik said.

But with every new person it infects, the coronavirus also has more chances to mutate, and therefore more chances to happen upon mutations that give it an advantage — by making it more transmissible, for example, or less susceptible to the immune system.

“If you have enough of that going on, huge amounts of virus replication throughout the world, then you are going to get many different variants,” said Dr. Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston.