The positivity rate of diagnostic testing for COVID-19 has dipped back below Minnesota's warning threshold — a sign of progress amid continued efforts to vaccinate residents against the infectious disease.

The rate dropped to 4.9% on Minnesota's response dashboard, a decline from 15.5% on Nov. 10 amid a second wave of the pandemic that has now caused 6,140 deaths and 458,633 known infections. The state totals include 16 deaths reported Thursday and 1,335 infections with the novel coronavirus that causes COVID-19.

The state on Thursday reported that 320,347 Minnesotans have received at least the first of two-dose COVID-19 vaccines, which were first prioritized for health care workers and long-term care residents but now have been offered in limited capacities to all senior citizens and teachers.

The state also reported that at least 85,217 people have completed vaccination, and that its total supply of federally controlled vaccine is now 826,625 first and second doses.

"Given that our supply is so limited, and is such a scarce resource right now, I feel like it's gone as well as it probably could," said Dr. Mark Sannes, a leader of the COVID-19 response for the Bloomington-based HealthPartners system.

Health systems are completing vaccinations of health care workers while offering limited open appointments to people 75 and older.

Meanwhile, the state has set up a mass vaccination site at Xcel Energy Center in St. Paul, to give first doses to 15,000 metro-area educators this week, and nine sites statewide to give shots to nearly 10,000 senior citizens and rural teachers.

State health officials have taken steps to increase the rapid administration of vaccine amid concerns that new genetic variants of the SARS-CoV-2 virus could help fuel another wave of the pandemic.

Gov. Tim Walz this week challenged providers to administer 90% of their first doses within three days of receiving them, and 100% within seven days. On Thursday, six of 11 major Minnesota health systems were meeting the seven-day goal but only four were meeting the three-day goal.

HealthPartners was just barely meeting the three-day goal — administering 92% of doses in that time frame. Sannes said that is a challenging goal for any providers receiving their shipments late in the week.

"Using it all up in seven days is a reasonable expectation given how these shipments arrive on a weekly basis," he said. "It may be a challenge to get everybody in in those three days."

The positivity rate of diagnostic testing is a key measure of viral activity in Minnesota, which has considered 5% as a warning threshold. The rate had briefly dropped below that threshold on Dec. 24 before rising again after the holidays. Walz last fall had said a rate below 4% would be one indication that Minnesota could dial back some of its social distancing and business capacity restrictions.

The pandemic has taken a particularly harsh toll on people 70 and older, who have suffered less than 10% of the diagnostic infections but more than 80% of the COVID-19 deaths. Fifteen of the deaths reported Thursday involved people older than 70, but one involved a Hennepin County resident in the 35 to 39 age range. In total, the state has reported only 45 COVID-19 deaths in people 39 or younger.

Twelve of the deaths reported Thursday involved residents of long-term care, who have suffered 64% of the total COVID-19 deaths in Minnesota due to their age and underlying health conditions. Nine of the deaths involved Minnesotans in the seven-county Twin Cities metro area while the rest were in other regions of the state.

Jeremy Olson • 612-673-7744