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The coronavirus variant that has pummeled Britain was identified Wednesday in Southern California, the second confirmed infection in the United States of what scientists believe to be a more contagious strain of the pathogen.

The news broke just hours after Colorado officials revealed they are investigating their second suspected infection involving the variant, and as federal officials pledged to ramp up their monitoring of coronavirus mutations.

The California case involved a 30-year-old man who was tested Wednesday, officials said. He had no known travel history. The same is true of the two people involved in the Colorado cases. That suggests the variant, believed by scientists to be more transmissible but not more likely to sicken or kill, is freely circulating in some communities in the United States.

“Because there is no travel history, we believe this is not an isolated case in San Diego County, and there are probably other cases of the same strain in San Diego County,” County Supervisor Nathan Fletcher said at a news conference.

The rapid-fire developments in two states underscored the need to improve the country’s scattered surveillance of the coronavirus, which jumped from an unknown animal into the human species late last year and appears to be evolving as it adapts to its new host.

“Just an hour or so ago we were informed that this new variant, this new strain that we’ve identified obviously from the United Kingdom … has been identified here in the state of California, in Southern California,” Gov. Gavin Newsom said on a Facebook Live broadcast.

California Gov. Gavin Newsom (D) said Dec. 30 that a new variant of coronavirus, known as B.1.1.7, had been “identified” in the state. (California Governor/Facebook)

Federal health officials said that a new surveillance system, created by the Centers for Disease Control and Prevention in November to track new variants of the coronavirus, will eventually be able to analyze as many as 3,500 virus genomes per week to look for mutations of interest — a capability scientists say is essential to identify and protect against new strains with mutations that might evade testing and be impervious to vaccines or certain treatments.

In a statement released Wednesday in response to questions about the pace of the program, the CDC did not offer a timetable, saying it “has been working on the surveillance for several months and has some components in place. This is the time to accelerate the process to better help public health and safety.”

Both the U.K. variant and one spreading rapidly in South Africa are believed by scientists to carry mutations that enhance transmissibility for reasons not clearly understood. However, they are not thought to change the severity of the illness, or pose any issues for the efficacy of the newly developed coronavirus vaccines. They also do not appear able to cause reinfections in people who have already survived a recent bout with the virus.

But a more transmissible virus means more infections, an unwelcome development amid the cold-weather surge of cases, hospitalizations and deaths in the United States and many other countries trying to survive this brutal pandemic winter.

The variants “could lead to more cases and put even more strain on our heavily burdened health-care systems,” said Henry Walke, head of the CDC’s response to covid-19, the disease caused by the virus.

The United Kingdom variant, named B.1.1.7, has been identified in at least 19 countries. Walke said that no one knows how widely it has actually spread in the United States or globally. The South Africa variant has been seen in a total of four countries, but not in the United States so far.

He and others said the identification of the variant in this country should spur people to follow guidelines designed to limit the virus’s spread.

“If there was a reason to work really hard on stopping community transmission, we have an even better reason now, because we’re up against a more formidable enemy,” said Francis Collins, director of the National Institutes of Health. “Things are getting bad enough already, just from the previous viral strain.”

Colorado authorities echoed those admonitions on Wednesday as they described their scrutiny of a second case they described as “highly suspicious.”

Both infected individuals are members of the National Guard who were deployed Dec. 23 to the Good Samaritan Society assisted-living facility in Simla, Colo., in Elbert County, where all 26 residents tested positive for the familiar strain of the virus and four died, officials said.

The facility confirmed that an “allied health worker” tested positive with the new variant strain of the virus and said the state health department had been on site to test employees.

“We look forward to beginning vaccinations at this location next week,” said Randy Fitzgerald, regional vice president of the Good Samaritan Society.

State epidemiologist Rachel Herlihy said the new variant has not been detected among the facility’s residents. She said the two National Guard personnel were among six deployed to boost staffing and were not the cause of the outbreak, which began much earlier.

Herlihy added that it was not clear where the two people might have been exposed. Both are in isolation and recovering, officials said.

The fact that the individual with the confirmed infection, described as a man in his 20s, had no known travel history “logically implies that there’s more spread throughout the state,” said Anuj Mehta, a pulmonary and critical care physician at Denver Health who has been involved in the state’s pandemic response.

“We have to assume he got it from community spread,” Mehta said. “That could mean two other people had it, or it could mean 200 other people had it. Time will tell how widespread it is.”

Most mutations have no practical consequence. Since all viruses mutate, there are many variants of the coronavirus, known as SARS-CoV-2. But one mutation that appeared early this year is now seen in all new coronavirus cases, and many scientists say it enhanced infectivity. Now the United Kingdom and South Africa variants are seizing the attention of scientists and public health officials.

“We expect to see new variants emerge over time,” Walke said.

The U.K. variant, which contains 17 mutations, including some affecting the spike protein on the exterior of the virus, first appeared there in September and has become dominant across the country, leading to a lockdown in London and southern England and travel bans by other countries hoping to prevent its importation.

Officials in the United States, where surveillance of viral sequences is spotty, say they are not surprised it has been detected in this country.

“I would have been amazed if this variant was not present in the U.S. given that it’s been bouncing around in the U.K. since September and people do go back and forth,” Collins said.

At least one epidemiologist said it is unlikely the new variant is a driving force in the disease surges in Los Angeles and other locations. Although the United States is sequencing only a small fraction of cases — and missing many infections because people are asymptomatic — the new strain would probably have been picked up if it had spread at that scale, said John Brownstein, an epidemiologist and chief innovation officer of Boston Children’s Hospital.

But given the paucity of sequencing, finding one or two cases in Colorado suggests there are several hundred that have been missed, he said.

“It could drive a future surge, especially given the challenges with the vaccine rollout,” Brownstein said. He added that greater numbers of infections also translate to additional opportunities for the virus to mutate in potentially problematic ways. “The sheer amount of transmission allows more chances for it to mutate,” he said.

Among those problems could be reduced effectiveness of monoclonal antibodies, as mutations may affect how they neutralize the virus, said Jesse Goodman, who directs the COMPASS program at Georgetown University, which focuses on science-based public health policy. Some monoclonal antibody treatments, such as the one President Trump received when he had covid-19 and hailed as a cure, contain more than one antibody, making resistance less likely to develop.

Goodman said that although preliminary evidence suggests the changes in the new variant are unlikely to reduce the vaccines’ effectiveness, that may not be true of future mutations. Still, the messenger RNA platform used in two newly authorized vaccines is comparatively easy to modify to handle mutant strains, he said.

“We are still learning every day about this virus,” Goodman said. “We don’t know when or how often we may need to make changes in a coronavirus vaccine.”

Bruce Gellin, president of global immunization at the Sabin Vaccine Institute, said the shifts in the coronavirus reflect a pattern that mimics what goes on with influenza, where scientists routinely monitor changes in the strain.

With other coronaviruses — such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), the current strain of the novel coronavirus and now the new variant — scientists are constantly playing catch up, said Gellin, who advocates a Manhattan Project-type approach to produce a universal vaccine that could protect against any strain of the coronavirus or flu.

“We need to have an approach that will prevent these problems before they show up, rather than quash after they arrive,” he said.