Worrisome signs are surfacing that a more contagious version of the pandemic virus is spreading in Minnesota, even as the state continues to see fewer COVID-19 deaths and cases.

The Minnesota Department of Health announced last week that the number of B.1.1.7 variant cases confirmed across the state more than doubled in one week from 18 to 40. The state public health lab, meanwhile, is performing genetic sequencing on a growing number of samples used in tests where the results suggest the variant might have caused infections.

First detected last year in the United Kingdom, the variant has raised worries the pandemic might accelerate and intensify despite growing protection from vaccines.

"I'm fearing we're at the beginning of an exponential curve," said Sara Vetter, interim assistant director of the state public health lab in St. Paul. "Maybe I'm wrong — maybe next week it will be really low. But between these two weeks, it appears that we're doubling."

While the variant's spread was not unexpected, the one-week surge in known cases is troubling, Vetter said.

Some of Minnesota's first cases were connected with travel, but health officials say more variant infections now stem from spread within the state. They believe that given limited surveillance, there are more cases of the variant in Minnesota than have been identified thus far.

"This variant is associated with more transmission and in the U.K. was associated with increased severity," Dr. Ruth Lynfield, the state epidemiologist, said. "We do not want to be in a situation of exponential growth again, especially with a variant that may be more severe."

Lynfield added: "We should be concerned and we should use this concern to be vigilant in prevention measures."

The Health Department on Saturday reported 884 new coronavirus cases across the state and 11 more deaths linked to COVID-19. The seven-day rolling averages for new cases and deaths are at levels last reported in September, down sharply from peaks in November and December.

The statewide tally for people who have received at least one vaccine dose increased by 14,679 in Saturday's data release, for a total of 742,760 people so far. That's about 13.4% of the state's population, according to Star Tribune estimates.

Health experts have expressed varying degrees of concern about future cases with the emergence of coronavirus variants from the U.K., South Africa and Brazil, all of which are thought to be more contagious.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, has focused on the B.1.1.7 variant, which seems to be outpacing the others. The federal government is reporting a total of more than 1,500 cases of the B.1.1.7 variant across 42 states, including more than 400 in Florida.

In recent weeks, Osterholm has said the emergence of the variant could drive a surge of cases in the coming months. Cases from B.1.1.7 across the U.S. are starting to double about every 10 days, Osterholm said in a podcast last week, adding that the U.K. knocked down growth in variant cases only with a stringent lockdown.

"Beyond the horizon is this dangerous Category Five hurricane — it's there," he said during the podcast. "The hurricane, of course, is the new variants of COVID-19."

But Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, said the variants might simply slow the rate at which case numbers are falling.

"I think that the vaccine and natural infection provide enough immunity that we're not going to see huge numbers of cases of these new variants coming through," Pekosz said during a Thursday call with reporters.

David Montefiori, a virologist at Duke University, said there continues to be much uncertainty about the variants. While the strain that's emerged in South Africa is particularly worrisome for evading some protection created by vaccines, Montefiori said, the shots "work just as well" with the U.K. variant.

Some regions in the U.S. might be hit harder by variants than others, said William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, who said he's closely watching the situation in Florida. But coronavirus infections, in general, tend to peak in January, Hanage said, and protection from vaccines is growing.

"I don't think there's going to be a definitive national surge, at least not in the next few months, but there may well be locally significant events." he said last week.

Dr. Jonathan Temte, an associate dean for public health at the University of Wisconsin, called B.1.1.7 a "significant threat," but said there's also a "delicate interplay" between existing immunity, the vaccines, adherence to public health measures, seasonality of the virus and varying risks for different subgroups of the population. He added via e-mail that the situation should become clearer over the next two weeks "as we are detecting significant increases in B.1.1.7 across Minnesota and Wisconsin."

The variant threat is one reason Osterholm has joined other health experts in saying the U.S. should consider delaying second doses of vaccines so more people can get first shots quicker.

The idea is controversial and prompted the New England Journal of Medicine last week to publish opposing articles on the question while posting an online poll for readers. As of Saturday afternoon, nearly 7,500 people — not necessarily all doctors — had responded with 53% supporting the standard two-dose regimen and 46% recommending a delay in second doses.

The U.S. is quickly trying to expand sequencing work to better monitor variants. Minnesota's public health lab increased the number of genetic sequences it runs each week from about 50 to 90 in January to about 150 per week now, said Vetter of the state public health lab.

The lab has a goal to increase the weekly count to 300 genetic sequences in the coming weeks, she said.

Christopher Snowbeck • 612-673-4744