Minnesota has more COVID-19 showing up in its wastewater, but worsening trends haven't yet produced the severe outcomes of previous pandemic waves.

Sampling at the Metropolitan Wastewater Treatment Plant in St. Paul found an 11% increase over the past week in the average amount of viral material in sewage, according to an update on Friday. Rising levels were detected this week in all seven surveillance regions across Minnesota as well, based on sampling at 40 treatment plants accounting for 67% of the state's population.

The highly transmissible BA.2 coronavirus subvariant is responsible for 97% of the viral material found in sewage in the Twin Cities, but sampling identified the first traces of a faster-spreading BA.2.12.1 variant that is driving up COVID-19 cases in the northeastern United States. Genomic sequencing of positive specimens from Minnesotans with COVID-19 also found this variant in eight cases earlier this month.

Neither variant is producing the level of COVID severity Minnesota encountered in earlier pandemic waves, and health officials believe high immunity levels from infections and vaccinations are playing a protective role. Minnesota reported 276 COVID-19 hospitalizations on Thursday, an increase from 183 on April 10. However, only 8% of the hospitalizations required intensive care, compared with a peak rate of 30% at different points last year during the delta variant wave.

"What we're seeing in the hospital is different than last fall and last winter right now," said Dr. Mark Sannes, an infectious disease specialist with HealthPartners, which operates Regions Hospital in St. Paul and Methodist Hospital in St. Louis Park.

"About half of our patients that have been identified by testing as having COVID are in with something other than COVID — so their clinical syndrome is something else," he added.

Minneapolis-based Allina Health similarly reported an increase over the past three weeks in the positivity of outpatient COVID-19 testing from 3.8% to 8.2%. However, the increase hasn't produced a comparable rise in hospital admissions.

Wastewater sampling is considered a purer measure of COVID-19 activity than case counts, which can be thrown off by whether people with mild infections seek publicly reportable diagnostic tests. Right now, both measures agree on the trend.

The Minnesota Department of Health reported 1,979 infections Friday and the seven-day average of new infections increased from 374 per day in the week ending March 20 to 1,053 per day on April 23. Minnesota reported five COVID-19 deaths on Friday, raising its pandemic toll to 12,508. However, the seven-day trend of COVID-19 deaths has declined to two per day.

An estimated 61% of Minnesotans already have had COVID-19 over the past year or two, based on a re-examination of blood specimens submitted since early September for medical tests. Experts from the Centers for Disease Control and Prevention cautioned this doesn't mean 61% of Minnesotans are protected — because immunity wanes over time — and there doesn't appear to be any herd immunity rate that stifles the spread of the coronavirus.

"We would expect seroprevalence to continue to rise over time, ultimately approaching 100 percent," said Dr. Jefferson Jones, a CDC preventive medicine specialist, although some people after a year or two will end up with undetectable levels of COVID-19 antibodies in their blood.

Immunity through vaccination and infection is playing some role, especially because half of Minnesota's identified COVID-19 cases occurred since last fall, Sannes said. "It's why we are seeing a downturn in the severity of illness. We have a lot of folks that have immunity from a couple different mechanisms. The unknown remains: How long does that last?"

A CDC update Thursday showed that Olmsted and Wabasha counties in Minnesota were at high pandemic risk levels based on current infection and hospitalization rates. Minnesota and Wisconsin are the only states with high-risk counties other than in the Northeast, where the BA.2.12.1 variant is the dominant source of viral spread. Mask-wearing in indoor public spaces is recommended in counties with high levels.

While the rest of Minnesota is in the moderate or low range, Minneapolis responded to local trends on Thursday with a mask-wearing recommendation for the city.

A high-risk designation means hospitalizations have already reached concerning levels, so Minneapolis is trying to be "proactive" and encourage people to protect themselves before that happens, said Luisa Pessoa-Brandao, an epidemiology manager for the Minneapolis Health Department. "We know masks are a good way to tamp down transmission. Why wait until we are in a situation where we're at a high community level?"

Health officials encourage more people to seek COVID-19 vaccinations. The state is stuck at 49% of eligible residents 5 and older being up to date with vaccinations.