Minnesotans now have their first shot at signing up for a COVID-19 vaccine trial — with Bloomington-based HealthPartners announcing Wednesday that it is recruiting up to 1,500 adults for AstraZeneca's Phase 3 study.

HealthPartners is the fifth site in the trial to start recruiting participants, who would receive two doses either of the experimental vaccine or a non-medicating saline injection for comparison and would commit to a series of nine checkup visits over two years.

Earlier, smaller trials showed evidence of safety and immunity, said Dr. Charlene McEvoy, a HealthPartners pulmonologist and lead researcher for the local site.

"What we don't know is, does it work well in everyone? Is it well tolerated across the board?" McEvoy said. "The biggest question is, how long does that immunity last?"

HealthPartners' selection as one of 62 U.S. trial locations reflects the providers' history of clinical research but is also a bittersweet reminder that COVID-19 has spread broadly in Minnesota. Trials generally recruit only in states where there is enough virus activity to prove that an experimental vaccine works.

Minnesota as of Wednesday had recorded 77,085 lab-confirmed infections with the coronavirus that causes COVID-19, and 1,830 deaths. Despite some signs of viral activity leveling off in early August, the state has seen its confirmed infection rate double from six new cases per day per 100,000 people on June 16 to 12 cases now.

No Minnesota sites were selected by Moderna Inc. or Pfizer for their Phase 3 COVID-19 vaccine trials. Minneapolis-based Allina Health is pursuing participation in a vaccine trial by the Janssen Pharmaceutical Companies of Johnson & Johnson later this year.

HealthPartners is seeking to complete recruitment in eight weeks, largely through its website — with priority going to participants such as waiters who work in higher-risk, higher-contact professions. The trial also is targeting a quarter of its enrollment for people 65 and older and minorities — two demographic groups that have shown higher rates of COVID-19 complications and deaths.

AstraZeneca's goal is to have initial safety and effectiveness results by the end of the year or early 2021.

The accelerated pace of vaccine development, with financial support from the federal Operation Warp Speed program, has health officials hopeful of enough positive trial data to offer a COVID-19 vaccine within months — perhaps with an emergency use authorization by the U.S. Food and Drug Administration rather than full approval.

However, health officials warned that such decisions must be made free of political influence — or the appearance of such influence that could undermine public confidence.

"That not only can interfere with uptake of the vaccine and its broader public health benefits, it may actually undermine confidence and trust in vaccines more broadly, which would be devastating," said Dr. Margaret Hamburg, former FDA commissioner under President Barack Obama, at a forum arranged last week by the University of Minnesota Center for Infectious Disease Research and Policy.

The FDA was criticized by some health officials last week for moving too swiftly in its approval of an emergency authorization of convalescent plasma, although the decision was based on early data from Mayo Clinic showing that it offered a benefit for hospitalized COVID-19 patients.

Vaccine approval will only be step one, followed by rationed distribution of initial doses to those at greatest need.

Minnesota health, policy and pharmacy leaders participated in a discussion with federal health and defense officials last week about how to prioritize early doses — particularly for health care and long-term care workers so they can safely care for others who are infection risks.

Consistency in distribution across states will be important yet the definition of high-priority groups might differ, said Kris Ehresmann, state infectious disease director. "In Minnesota, it may be that our snowplow drivers are determined to be critical, whereas Hawaii, that would not be an issue for them at all."

The AstraZeneca experimental vaccine, developed by researchers at Oxford University in England, seeks to boost both production of antibodies in response to the SARS-CoV-2 virus and of T-cells that help the body adapt and respond to infections.

McEvoy said the earlier safety studies showed some potential for mild side effects such as aches or mild fever — akin to what some people experience each year with seasonal flu shots.

People in the trial who test positive for COVID-19 at checkups would participate in remote monitoring to see when symptoms develop and if they are severe, Mc­Evoy said. They would receive monitoring equipment for their temperature, breathing rate, heart rate and oxygen level.

"Maybe the vaccine won't prevent illness but it will make it much less severe" in some people, she said.

The trial is blinded, meaning neither participants nor researchers know who has received the experimental vaccine or the placebo. Participants would receive up to $1,000 for travel and expenses related to clinical visits, which would include routine blood draws to check for antibody levels and indications that the vaccine is working.

Multiple trials are proceeding under the assumption that some won't work, or that some vaccines will work better in certain demographic populations than others.

The first vaccine to gain approval might not be the best one, said Nicole Lurie, a former disaster preparedness official for U.S. Health and Human Services, during the U forum last week, but it will be harder and take longer for subsequent vaccine candidates to complete their trials.

"Ultimately, we would like to see a one-dose vaccine that performs well across different populations," she said.

Mayo and the U are not part of any ongoing COVID-19 vaccine drug trials, but each has ongoing research about alternative forms that could require their own trials.

The federal government has already made large purchase orders for 100 million vaccine doses each from Pfizer and Moderna, though there is no proof yet that their versions work. Ehresmann said that will expedite distribution if one receives FDA approval.

"In the case of the COVID vaccine, the federal government has made the decision to carry that financial risk and to say, 'We want you to start manufacturing,' " Ehresmann said. " 'We know that some of these vaccines won't meet the safety protocols, and we'll just lose that money. But we want to have a vaccine that is ready to go as soon as it does meet the safety profile.' "