Four Twin Cities metro counties are among 21 in Minnesota considered to pose at least moderate COVID-19 risk based on infection and hospitalization rates.

Hennepin, Carver, Scott and Washington counties were all listed at moderate risk by the Centers for Disease Control and Prevention, while indoor mask-wearing was recommended in Pennington County in northwestern Minnesota because of high risk.

The latest CDC risk data matches wastewater sampling across Minnesota that is showing more evidence of the coronavirus that causes COVID-19. The Metropolitan Wastewater Treatment Center in St. Paul reported on Friday a 21% increase in the average viral load in sewage that was sampled over the past week.

State leaders remained hopeful, though, because COVID-19 hospitalizations and deaths haven't increased at the same rate. Of the 297 people hospitalized with COVID-19 in Minnesota on Thursday, 24 needed intensive care.

Gov. Tim Walz said vaccination progress has likely reduced the rate of infections that cause serious hospitalizations and driven Minnesota's COVID-19 death rate to its lowest level in the pandemic. The state's numbers have been at their lowest during the summers over the past two years, he added.

"If this thing tracks itself, we should see a lull here over the summer," Walz said Wednesday before receiving his second COVID-19 booster. "We're probably going to see spikes in the southern states coming up very shortly in the summer months when they move inside, and then our preparations are for [increased viral activity in] October."

Not everyone is as optimistic. New, faster-spreading variants could emerge and upset any apparent seasonal patterns, said Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy.

"It's impossible to predict what will happen," he said.

The fast-spreading BA.2 coronavirus subvariant made up 97% of the viral material found in the Twin Cities' wastewater samples over the past week. About one fifth of the BA.2 viral material involved an even faster-spreading form called BA.2.12.1, which has caused elevated COVID-19 activity in the Northeast.

Wastewater sampling has proven over time to be a faster indicator of COVID-19 trends — revealing the start and the peak of this winter's omicron pandemic wave a week or so before infection numbers shifted.

Wastewater and infection numbers are in sync right now. The viral load in Twin Cities wastewater has been rising but remains four times lower than at the peak of the omicron wave. The seven-day average of new infections in Minnesota has risen from 374 per day in the week ending March 20 to nearly 1,600. The rate was 13,000 per day in mid-January.

Minnesota reported four more COVID-19 deaths on Friday, raising the state's pandemic toll to 12,525. More than 80% of the deaths have been among seniors, but Friday's report included a Ramsey County resident in the 45 to 49 age range.

Walz encouraged people to protect themselves with vaccinations, which have shown in studies to reduce COVID-19 hospitalizations and severe illness even in people who have already been infected. Almost 1.5 million Minnesotans have tested positive for coronavirus infections since the start of the pandemic in March 2020, but federal estimates indicate as many as 3.3 million people in the state actually have been infected.

Minnesota reported Friday that 3.9 million Minnesotans have received at least a first COVID-19 vaccine dose and 2.5 million are up to date, meaning they have completed the initial vaccine series and received boosters as recommended. Another 250,000 Minnesotans have received second boosters, which the CDC approved to maintain immunity for people 50 or older, with weakened immune systems, or who only received the less-effective Johnson & Johnson vaccine.

The CDC's weekly risk designations are based on local infection and hospitalization rates, and are primarily designed to warn communities when their hospitals might be at risk of being overburdened by COVID-19. The measure has shown volatility; southeastern Olmsted and Wabasha counties were listed at high risk last week but downgraded this week.

Minneapolis issued an indoor public mask-wearing recommendation a week ago in expectation of rising infection numbers and a CDC high-risk designation at some point for Hennepin County. The rate of people always wearing masks in Hennepin increased slightly over the past week to 39% while the statewide rate is 28%, according to COVIDcast survey data.