Medical specialists said Tuesday that a recently emerged variant of the coronavirus is unlikely to be more deadly than the previous strain and will probably respond to the vaccines now being distributed, but that its ability to spread more easily means more people could catch the dangerous virus.
As the US confronts its first known case of the mutated variant — this one in Colorado — Boston-area doctors who are studying the pandemic said the development is concerning but not surprising. They encouraged people to continue taking precautions such as social distancing, wearing face masks, and frequently washing their hands.
“Even with this new variant, high filtration masks will still stop transmission,” said Dr. Abraar Karan, an internal medicine physician at Harvard Medical School and Brigham and Women’s Hospital. “Physical distancing, better ventilation — all of the strategies that we’ve been talking about already — are all the more important.”
After first being identified in the United Kingdom in September, the mutated variant, which is roughly 55 percent to 70 percent more easily transmitted than other strains of COVID-19, led to an emergency lockdown in London over Christmas.
Colorado’s governor announced Tuesday that the first case of the variant in the United States had been found in a man in his 20s who had “no travel history” and is in isolation in Elbert County.
This month, Maria Van Kerkhove, the World Health Organization’s technical lead on COVID-19, told the BBC that the vaccines now being distributed likely would be effective against the variant virus, and several drugmakers said they believed their vaccines’ efficacy would remain unaffected.
Karan said the vaccines are likely to work on the variant but added, “I think it’s too early to say with certainty.”
“We suspect that the vaccine should still be highly effective against this, but we just don’t know for sure yet,” he said.
The variant caused 62 percent of COVID-19 infections in London in the first full week of December, up from 28 percent in early November, according to researcher Paul Hunter, a professor of medicine at the University of East Anglia’s Norwich School of Medicine.
After first being identified in the UK, the variant was soon found in more than a dozen other countries, including Australia, Canada, Germany, Italy, Japan, Lebanon, the Netherlands, Singapore and South Korea.
It was inevitable that the variant would reach the United States, Karan said. “It was just a matter of time for us to sequence it and detect it.”
Since the Colorado man reportedly had not been traveling, he likely was infected through community spread, suggesting that the variant has been in the United States for some time, doctors said.
“This is incredibly concerning because it probably only represents the tip of the iceberg,” said Dr. Cassandra M. Pierre, an assistant professor of medicine at Boston University School of Medicine and a physician at Boston Medical Center. “We believe that there probably are more variants within the United States.”
So far only “a small fraction” of coronavirus infections are subjected to genetic sequencing, Pierre said, so it’s unclear how many variants of the virus exist.
“There could be many more out there,” she said. “We don’t know.”
Karan said his concern is that a more easily spread virus will mean more people become sick enough to require hospitalization, leading to overwhelmed hospitals.
International travelers could bring more cases of this or other COVID-19 variants into the country, and domestic travel over state lines could spread variants around the country, Pierre said.
New travel restrictions could help slow that spread, she said, but it’s too late to do anything about the holiday trips that many Americans have made in recent days. And to make interstate restrictions more effective, there needs to be much more genetic sequencing of the virus to determine where variants are present, she said.
Karan said travel restrictions can be effective if put in place quickly, but the apparent community spread of the variant in Colorado suggest that it’s too late for such measures to work. And travel restrictions can have unintended consequences, leading to overcrowding on routes of travel that are abruptly shut down or that remain open when other routes are closed.
Asked whether Massachusetts was considering new travel restrictions in response to the Colorado case, a spokesman for Governor Charlie Baker pointed to the Commonwealth’s existing rules for visitors from out of state.
“Massachusetts has implemented strict travel restrictions that require travelers to the Commonwealth to quarantine or produce a negative COVID-19 test result unless they meet a limited number of exceptions,” the spokesman, Terry MacCormack, said in an e-mail. “The Administration has contacted the CDC and the federal government requesting more information about the new variant.”
The variant has not been associated with a higher risk of death, though its higher transmission rates will inevitably lead to greater numbers of people dying, Pierre said.
“The more people who are infected, the more hospitalizations we will have, and … more deaths will come with that,” she said. “It’s a question of numbers rather than the overall virulence of the strain.”
Material from Bloomberg News was used in this report.
Jeremy C. Fox can be reached at email@example.com. Follow him on Twitter @jeremycfox.