Pictures of huddled, unmasked teenagers at a high school prom prompted warnings Thursday from Minnesota health officials about the risks of the pandemic and the need even for teenagers to be careful and seek out a vaccine.

Although the latest pandemic wave appears to be easing and teens are at lower risk of severe COVID-19, a lack of caution in this age group could upset Minnesota's progress, said Kris Ehresmann, state infectious disease director.

"We need people to do their part, even when it's hard, especially when it's hard," she said, encouraging mask-wearing in crowds, social distancing and staying home when sick to reduce chances for viral transmission.

More than 1,000 COVID-19 infections have been reported in pre-K through 12th-grade levels in Minnesota in each of the last two weeks, according to a weekly report released Thursday by the Minnesota Department of Health. Those numbers exceeded the weekly counts during the severe pandemic wave late last year and raised concerns about school-age children and teens fueling viral spread.

The state on Thursday reported 15 COVID-19 deaths and 1,921 infections with the coronavirus that causes the respiratory disease — raising Minnesota's pandemic totals to 7,128 deaths and 573,938 known infections.

State health officials hoped to make COVID-19 prevention easier for teens on one front this week by prioritizing access for 16- and 17-year-olds at appointments for the Pfizer vaccine at the Mall of America site. Only the Pfizer vaccine is approved for those ages. The cutoff for the Moderna and Johnson & Johnson vaccines is 18.

Gov. Tim Walz on Wednesday said teens are important to Minnesota's goal of a statewide 80% COVID-19 vaccination rate that could stifle the spread of the virus.

"To get to herd immunity we need to protect as many people as possible, and that includes teens," Walz said.

Pictures from last weekend's Marshall High School prom showed students, indoors and outdoors, huddled without masks. Ehresmann said health officials checked and found that the school did enforce COVID-19 protocols and that some pictures were taken off-site.

One picture showed 20 students packed together in the high school cafeteria, but Marshall Superintendent Jeremy Williams said it was a brief moment before students were sent back to their tables. "At no time would we ever intentionally put our students' health and safety at risk," he said.

Health officials also are concerned about infections emerging from the outdoor demonstrations in Brooklyn Center following the April 11 fatal police shooting of Daunte Wright. Ehresmann said 11 infections have been found among law enforcement personnel and 11 among demonstrators who were at the site, although there hasn't been genomic sequencing done to link their cases.

The lack of infections following the George Floyd demonstrations last summer surprised health officials — given the amount of shouting and singing and even the police use of tear gas that caused heavy breathing — but new viral variants could elevate risks this year.

An estimated 60 to 70% of infections in Minnesota right now are believed to be caused by a more infectious B.1.1.7 variant first identified in England.

The state also has found 88 infections involving the B1351 variant first found in South Africa and 65 involving the P.1 variant first found in Brazil.

The hospitalization rate is higher in these two infection groups, and the average age of the hospitalized patients is only 37, Ehresmann said. "We're seeing these variants impacting younger ages, we're seeing higher case severity and we're seeing more evidence of domestic transmission."

Despite the emergence of variants, key indicators suggest the latest wave is easing. The seven-day average positivity rate of diagnostic testing in Minnesota has declined from 7.5% on April 8 to 6.4%.

Pressure on hospitals has lessened, too. The number of COVID-19 cases in Minnesota hospital inpatient beds had increased from 210 on March 6 to 699 on April 17, but declined to 644 on Wednesday.

Increased surveillance testing likely is padding the number of infections found in students, including in those who have no symptoms.

Deaths and severe cases are rare in children and teenagers, though Minnesota reported its third COVID-19 pediatric death this week, coincidentally in Marshall, of a first-grader.

State health officials said it is important to identify even asymptomatic infections in students to try to slow the pandemic and maintain in-person learning as well as proms and graduations.

Infection numbers involving pre-K-12 educators have not increased in this latest wave, largely because they were prioritized along with senior citizens for the earliest limited supplies of COVID-19 vaccine. Nearly 800 infections were found among pre-K-12 educators in the week ending Nov. 14, compared with less than 200 last week.

Minnesota on Thursday reported that more than 2.5 million people have received some COVID-19 vaccine — amounting to 57% of the state's eligible population — and that more than 1.8 million people have completed the one- or two-dose series.

Nearly 87% of senior citizens in Minnesota have received some vaccine — a key target group that has suffered 89% of the state's COVID-19 deaths. State health officials believe vaccination progress in that group explains why COVID-19 deaths have not increased over the past month at the same rate as infections and hospitalizations.

Jeremy Olson • 612-673-7744