HealthPartners has suspended its wildly successful recruiting of participants into a COVID-19 vaccine trial while the maker of the experimental vaccine reviews a potential adverse effect on a recipient in the United Kingdom.

The Bloomington-based health care provider filled 1,019 of its 1,500 slots in the national trial in 24 hours last week, reflecting concerns about a pandemic that could produce another wave of infections, hospitalizations and deaths this fall. At one point, the interest from Minnesotans helped crash the recruitment website.

However, the trial led by AstraZeneca and Oxford University was suspended while a review is underway of a participant who suffered an illness in the English arm of the trial.

"The trial sponsor has let us know that it is having a review and evaluation of the trial this week, so we are pausing enrollment for this to occur," said HealthPartners spokesman David Martinson. "Upon completion of the evaluation we will be able to reschedule patients."

AstraZeneca issued a statement late Tuesday noting that "our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee. This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials."

The trial news comes amid continued warnings by Minnesota health officials of a broadening spread of the virus. The Minnesota Department of Health reported Tuesday just two COVID-19 deaths and 387 newly confirmed infections — reflecting reduced testing over the holiday weekend — and 257 people hospitalized with the infectious disease. That is the lowest hospital count since late July.

Other trends in the pandemic are more ominous, though, including a rising positivity rate of COVID-19 diagnostic testing that is now at 5.6%. The rate of newly confirmed infections also has increased even as the rate of testing activity has decreased.

Virus strikes Winona State

Cases surged in Winona County from 243 on Aug. 1 to 622 now — with half involving young adults aged 18 to 24. Winona State University reported 97 confirmed infections as of Aug. 30 and announced a two-week quarantine on Tuesday in which most classes will temporarily shift online and most employees will return to remote work.

"The numbers are concerning," said Karen Sanness, Winona County Health and Human Services director, who has consulted with local colleges and with proprietors of bars, restaurants and other student hangouts on ways to control the spread of the virus.

"I'm just worried about seeing it spread into the older people in the community. We haven't seen that yet, but it's always a concern because then we're going to see more hospitalizations and we're going to see more deaths," she said.

COVID-19 is caused by infection with a novel coronavirus for which no vaccine exists. The state has tallied 81,608 lab-confirmed infections and 1,862 COVID-19 deaths — 80% of which have involved people 70 and older.

Three Phase 3 trials are underway in the U.S. to prove the safety and effectiveness of experimental vaccines, including the AstraZeneca trial.

The Minnesota Department of Health will closely monitor safety data regarding potential COVID-19 vaccines and is preparing for when the first vaccine is approved and how it will be distributed, said Kris Ehresmann, state infectious disease director.

"When the vaccine is first available it will be in limited supply, but we also know that as we move forward it will be really important that we have a large proportion of our population … vaccinated," she said.

If the review permits AstraZeneca's trial to proceed, HealthPartners plans to focus recruiting for its last 400 slots on minorities, the elderly and others at risk of severe COVID-19. Participants receive the experimental vaccine or a nonmedicating placebo for comparison, and then give blood samples and submit to checkups over two years to determine if the vaccine is protecting them. The trial has eyed people in high-contact jobs who are more likely to be exposed to the virus over time.

Not all patients were screened in. Gregory Johnston, 71, of Rockford, said he was motivated by his grandchildren and others to accelerate the discovery of a vaccine but was denied entry because of existing health conditions.

"I want to do what I can to get a vaccine out there for this terrible virus," he said.

Carmen Aguirre, 27, fit the high-risk profile as a University of Minnesota medical student but was ruled out because she has a chronic disorder.

Her boyfriend signed up, partly so he could protect Aguirre from getting infected, but is having second thoughts about a two-year commitment if he has a 50-50 chance of getting a placebo.

"We want to get the vaccine as soon as possible," Aguirre said.

Staff writer Ryan Faircloth contributed to this article.

Jeremy Olson • 612-673-7744