Stable or slightly increasing levels of COVID-19 in Minnesota are mostly driven by a fast-spreading BA.2 subvariant that has fueled outbreaks elsewhere in recent weeks.

Sampling of Twin Cities wastewater detected a 2% increase in viral load over the past week, and that 78% of the viral material involved BA.2. Friday's wastewater data from the Metropolitan Council agreed with the latest genomic sequencing results from COVID-19 testing labs that found BA.2 in 62% of infections in the week ending March 25.

The rising presence of BA.2 leaves Minnesota in a wait-and-see mode as COVID-19 numbers have flattened over the past two weeks. COVID-19 hospitalizations in Minnesota declined from a peak of 1,629 on Jan. 14 to 201 on March 25 but have hovered at that level for two weeks. There were 200 COVID-19 hospitalizations in Minnesota on Thursday.

"Some other states are starting to rise a bit now," said Curtis Storlie, a creator of the Mayo Clinic COVID-19 predictive model that forecasts a mild increase in coronavirus infections in Minnesota over the next two weeks. "I would be surprised if we didn't see a bit of an uptick in Minnesota in a month or so. Beyond that … it is always hard to say."

BA.2 is believed to spread 30% faster than an earlier version of the omicron variant that caused record COVID-19 cases in Minnesota this winter. The subvariant is largely responsible for recent waves in parts of Europe, but it's unclear if it will fuel an uptick in Minnesota.

Only 48.9% of Minnesotans 5 and older are considered up to date with COVID-19 vaccines, meaning they recently completed the initial series or received scheduled booster doses after earlier shots, according to state data. However, that vaccination rate combined with the large number of people with temporary immunity after recent omicron infections could shield Minnesota.

Variants of concern haven't always produced COVID-19 waves. The beta variant didn't spread widely in Minnesota last spring after it was identified in Brazil, but the delta and omicron variants emerged in the fall and winter and doubled the state's number of coronavirus infections to more than 1.4 million.

COVID-19 deaths in Minnesota increased from 7,734 through last June to 12,440, including six deaths reported on Friday. People younger than 60 made up only 8% of Minnesota's COVID-19 deaths through June, but 18% of the deaths since that time as they have been less likely to seek vaccine.

The state has reported 154 COVID-19 deaths in March, down from 1,078 in December at the peak of the delta wave and 517 in February.

Dr. Gregory Poland, director of Mayo Clinic's Vaccine Research Group, urged people to stay up to date with COVID-19 vaccines and avoid complacency over the improving numbers. In any other context, Americans would be shocked if 30,000 people were becoming sick per day and 500 to 1,000 were dying, he said.

"That is COVID as we know it right now, today," he said. "And what are we doing? We are pretending the pandemic is over."

Minnesota saw an uptick with nearly 40,000 COVID-19 vaccine doses administered last week after federal health authorities OK'd second booster doses to restore immunity levels. The state ranks second in the U.S. with 62% of fully vaccinated adults receiving first boosters to maintain immunity. However, more than 1 million Minnesotans 5 and older have received no vaccine, and some fully vaccinated people have lost immunity without boosters.

New variants such as XE already are emerging and could present threats even if BA.2 doesn't produce a COVID-19 wave. Poland said fully vaccinated people with low risks or recent breakthrough infections could wait and observe pandemic trends before getting a second booster, but people who are vulnerable to COVID-19 should consider it right away.

Wastewater sampling has become an increasingly important measure of pandemic activity as other statistical measures have weakened. Models based on COVID-19 cases have been challenged by the growth in at-home rapid tests, which aren't included in public tallies.

The positivity rate of COVID-19 testing has been a stable indicator of pandemic severity in Minnesota. But data from April 4 onward could be less reliable because some labs are no longer required to report negative test results that are used in the calculation.

Minnesota's positivity rate was 3% in the week ending March 30, well below the peak of 23.5% on Jan. 10 but also an increase from a low of 2.7% on March 20.