By Amy Orciari Herman

Edited by Susan Sadoughi, MD, and André Sofair, MD, MPH

A SARS-CoV-2 variant that was identified in the U.K. in mid-September and seems more transmissible than other strains led to strict lockdown measures in London and surrounding areas over the weekend, according to media reports.

The variant contains 23 genetic mutations, several of which affect the virus’s spike protein. It accounted for 28% of COVID-19 cases in London in mid-November, the Wall Street Journal reports. By mid-December, this had risen to 62%. “It is becoming the dominant variant; it is beating all the others in terms of transmission,” the U.K. government’s top scientific adviser said on Saturday.

A modeling analysis suggests it could be 70% more transmissible than other SARS-CoV-2 strains. But another U.K. scientific adviser was cautious: “I think we need to have a little bit more experimental data,” she told the New York Times. “We can’t entirely rule out the fact that some of this transmissibility data might be related to human behavior.”

In South Africa, a similar variant has been identified in 90% of samples analyzed, the Times reports. Scientists there also emphasized that “human behavior was driving the epidemic, not new mutations whose effect on transmissibility had yet to be quantified.”

U.K. scientific advisers said that for now, the new variant does not seem to cause more severe illness or fatality than other strains and it should not render vaccines ineffective. Nonetheless, a U.S. evolutionary biologist told the Times, “It’s a real warning that we need to pay closer attention.”