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A fast-spreading coronavirus subvariant appears to be pushing COVID-19 levels up in Minnesota — as it already has in warm-weather states this summer — but not hospitalizations and deaths so far.

Six of seven regions of Minnesota saw the viral load in wastewater increase Sunday — with the southwest and south-central regions reporting their highest levels on record, according to the University of Minnesota.

The growth is the work of the BA.5 subvariant, which was responsible for 71% of infections in the first two weeks of July, according to genomic sequencing of a sampling of positive COVID-19 specimens in Minnesota.

"Like other places in the country and world, we are seeing rapid emergence of this variant of concern," said Mark Osborn, the U microbiologist overseeing the statewide wastewater monitoring.

BA.5 has shown high breakthrough rates of infections in people with immunity from vaccinations or recent COVID-19 cases. More than 54% of infections identified in the final week of June in Minnesota involved people who had received initial vaccinations and boosters, according to the state Department of Health's weekly COVID-19 situation report, updated each Thursday.

Health officials remain optimistic that immunity provides some benefit by lowering the level of severe illness. Minnesota seniors who were not fully vaccinated were 10 times more likely to be hospitalized with COVID-19 in the past two months and seven times more likely to die of the infectious disease than seniors who had received the initial shots and booster doses, the health department reported.

COVID-19 hospitalizations in Minnesota have held steady for more than two months, reaching 406 on Tuesday and including 46 patients needing intensive care. The state reported another 35 COVID-19 deaths over the past week, maintaining its average of five per day — mostly in seniors.

Minnesota's total COVID-19 death toll stands at12,907.

BA.5 produced less severe illness than other variants when it was discovered in South Africa, but it has been harsher in other countries, said Michael Osterholm, director of the U's Center for Infectious Disease Research and Policy.

He discouraged complacency, noting that the current level of COVID-19 hospitalizations and deaths in the U.S. is low in the context of two years of the pandemic but would have been cause for concern earlier.

"It's like Minnesota winters" after a week of subzero temperatures, he said. "You get five days of 20 degrees, and you want to be outside with your coat off."

Vaccines remained protective against earlier omicron subvariants of the coronavirus such as BA.2, according to the latest results from Bloomington-based HealthPartners and nine other U.S. health systems. But their effectiveness waned with time.

COVID-related hospitalizations occurred from January through June in more than 7% of the health systems' unvaccinated adult patients compared with 3% of patients who had received COVID booster doses within six months.

The hospitalization rate rose to almost 7%, though, among patients whose booster shots were six or more months old.

The seven-day average of new coronavirus infections in Minnesota bottomed out at 1,197 per day in the week ending July 5, partly because of reduced testing over the Independence Day weekend. The average rebounded to 1,424 per day in the week ending July 11, the highest rate since mid-June.

July 4 has served as a pivot point for COVID-19's spread over the past two summers, presumably because group gatherings presented new infection opportunities for the virus.

The growth in reported infections is occurring despite the closure of some state testing centers and the rising use of at-home COVID-19 tests that aren't reported publicly.

Viral levels in wastewater are considered a more reliable indicator of changes in COVID-19 activity in Minnesota, reflecting the spread of the virus even among people who don't know they are infected. Sewage sampling has limits as well. The viral loads reached record levels in two southern Minnesota regions, but they are based on results from a combined seven treatment plants and can swing wildly.

The U monitoring data showed an increase in the Twin Cities metro region, based on results from 13 plants in suburbs such as Hastings and Cambridge. Wastewater results for the bulk of the area are reported separately on Fridays.

The CDC on Thursday reported that five Minnesota counties — Kittson, Wadena, Olmsted, Winona and Martin — have high enough infection and COVID-related hospitalization rates to merit high-risk designations and indoor mask-wearing recommendations. Martin is in the south-central region reporting high viral loads in wastewater.

Another 36 counties, including the north and west metro area, were listed at moderate COVID levels.