Teenagers are fueling a slight uptick in COVID-19 activity in Minnesota, which on Tuesday reported an increase in the positivity rate of diagnostic testing to 3.9%.

The Minnesota Department of Health has reported 6,818 more diagnosed cases of COVID-19 in the seven-day period ending Tuesday, and 10% involved teenagers 15 to 19 years old, whose risks for viral transmission increased earlier this year with the return to in-person classes and youth sports activities.

Since Feb. 1, no other five-year age bracket has sustained more confirmed infections with the novel coronavirus that causes COVID-19. Seven percent of infections reported in the past two weeks have involved children 10 to 14 years old — equating that age group's share of the total population for the first time in the yearlong pandemic.

While severe COVID-19 is rare among children and young adults, state health officials remain concerned about their ability to spread the infectious disease to others at greater risk.

State Health Commissioner Jan Malcolm said basic prevention measures such as mask-wearing and social distancing are still needed to slow viral transmission even as schools reopen and bars, restaurants and entertainment venues are allowed to host larger groups.

"We just need to keep attending to those basic prevention steps that we know are so critical for helping to control spread of the virus as we continue to make progress on vaccinations," she said.

The state on Tuesday reported that 1,265,430 people in Minnesota have received COVID-19 vaccine, and 729,294 have completed the series either by receiving two doses of the Moderna and Pfizer versions or a single dose of the Johnson & Johnson vaccine.

An estimated 76% of Minnesota's senior citizens have received at least a first dose — having been prioritized for vaccination because their age group has suffered 89% of the state's COVID-19 deaths.

The state on Tuesday launched its sixth permanent COVID-19 vaccination site at River's Edge Convention Center in St. Cloud and will use its Connector database to identify people who are eligible for shots and send appointment invitations.

Priority groups for vaccine include health care workers, educators, long-term care residents, seniors and non-elderly adults with certain underlying health conditions or high-risk occupations. Alternatives for vaccination include clinics, public health events and pharmacies — including five chain pharmacies that are part of a federal vaccine distribution program in Minnesota.

Minnesota in total has reported 498,926 diagnosed infections and 6,749 COVID-19 deaths, including 716 infections and two deaths that were added on Tuesday.

The positivity rate of diagnostic testing for COVID-19 rose from 3.5% to 3.9% in early March, but remains below a state caution threshold of 5% for viral activity.

Some of the growth in teen COVID-19 cases is fueled by more aggressive testing in that population and the identification of asymptomatic cases.

Following the reopening of many schools to in-person learning, the Minnesota Department of Health recommended that K-12 students seek testing once every two weeks and that young athletes seek testing weekly and three days before any competitions.

"If we're going to stay ahead of this, all young people across the state should be getting tested," said Dan Huff, assistant state health commissioner. "It's how we avoid more pauses in sports and how we keep our kids in the classroom."

State data through the week ending March 6 showed an increase in both the rate of testing in the 10- to 19-year-old group and the positivity rate of the results. Increases in both numbers at the same time are signals to health officials that viral activity is actually increasing beyond any growth in testing.

An outbreak in Carver County has been centered on youth sports activities, but it includes viral transmission that occurred at schools, fitness clubs, child care centers and other locations.

At least 32 of 140 cases in that suburban outbreak have been found through genomic sequencing of lab samples to involve a more infectious B.1.1.7 variant of the virus that causes COVID-19. Samples from another 67 cases were pending as of Monday.

More than 250 infections traced to that variant have been identified in Minnesota, which is a concern because that viral variant spread rapidly among teens and young adults when it was first identified in England, said Michael Osterholm of the University of Minnesota's Center for Infectious Disease Research and Policy.

"We are actually seeing a higher proportion of younger-aged cases being hospitalized" in areas where that variant is spreading, he added.

Variant concerns did not dissuade Gov. Tim Walz last week from rescinding some COVID-19 restrictions that among other things will allow fans back in professional arenas and concert venues again.

Malcolm said rapid spread of variant-driven COVID-19 could end up being manageable without more restrictions if enough older and high-risk people are vaccinated and hospitalizations don't increase.

"Whether the cases produce the same pattern or different patterns, more or less because of the variants and the vaccine, will be very important," she said.

Educators have been prioritized for early supplies of COVID-19 vaccine, in part to protect them so they can safely teach live classes. About 64% of K-12 and preschool educators had received vaccine last week.

Vaccination of senior citizens also partly explains why teens are making up a greater proportion of COVID-19 cases reported each week in Minnesota. People 70 and older made up 10% of all infections reported in December, but only 5% of cases reported in the last week.