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Coronavirus levels in Twin Cities' wastewater increased 36% over the past week, defying other signs of pandemic progress in Minnesota and also revealing the presence of the BA.2.75 variant in the state.

Friday's reported increase brings viral loads found at the Metropolitan Wastewater Treatment Plant in St. Paul back to levels seen in mid-August, so it could just be a correction following recent declines. The increase also could be exaggerated by an unusually high reading from sewage samples on Sept. 9 alone.

But health officials didn't rule out the start of a fall COVID-19 wave following the social interactions of the Minnesota State Fair and Labor Day weekend. Gov. Tim Walz and Lt. Gov. Peggy Flanagan received recommended booster shots Friday, and urged other Minnesotans to do the same before any fall increase in COVID-19.

"This is the best defense about keeping folks out of the hospital. It's the best defense if we ... see a surge in the fall," said Walz, before receiving his Moderna booster at the State Capitol.

All of the governor's vaccinations have been public events, including his single Johnson & Johnson shot at the Minnesota Vikings training facility last year and his prior boosters at a Cub pharmacy in Minneapolis and then at St. Paul Corner Drug. Walz also had a bout with COVID-19 last December.

The newly recommended boosters are for fully vaccinated people 12 and older and contain additional protection against the omicron BA.4 and BA.5 viral variants. The latter variant was responsible for 90% of the viral material identified in wastewater at the Metro plant in the seven-day period ending Monday.

The boosters are not specifically formulated against BA.2.75, another omicron variant that is being closely monitored because it caused rapid viral spread in other countries. The metro plant found its first signs of that variant, which made up 1% to 2% of the viral load in wastewater sampled over the past week.

Six infections have been identified with the variant as well, based on the state's genomic sequencing of a sampling of specimens from positive COVID-19 cases, according to the Minnesota Department of Health.

BA.2.75 is in the omicron lineage of coronavirus subvariants, making it more similar to the new booster and more likely that the shot still will offer elevated protection, said Dan Huff, state assistant health commissioner.

"It's really about charging your immune system so that it can recognize the coronavirus," he said. "So it's still effective, although it's going to be more effective against BA.4/BA.5."

While omicron variants spread quickly, they have proven less severe than others such as the delta variant — which caused a prolonged COVID-19 wave last fall that increased the rate of deaths among younger, mostly unvaccinated adults in Minnesota.

COVID-19 death rates have declined among all age groups since last winter, but remain highest for seniors. People 65 and older made up more than 90% of Minnesota's COVID-19 deaths this summer.

Other COVID-19 indicators in Minnesota offered more optimism than the metro plant's wastewater results this week. Aggregate wastewater results from 40 other treatment plants showed declining viral loads through Sunday in six of seven reporting regions in Minnesota. A slight increase emerged in the northeast region after weeks of declines there as well.

The state's weekly situation update Thursday showed that the number of infections had declined from more than 1,400 per day for much of the summer to less than 1,200 per day at the end of August.

The infection data is a lagging indicator of pandemic activity, though, and the latest numbers don't account for more recent viral spread. Wastewater sampling is considered a predictive indicator of COVID-19 trends because it isn't dependent on the number of people seeking publicly reported tests for infection.