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BLOOMINGTON, Minn. — A Minnesota health care provider has suspended its successful recruitment of participants in a coronavirus vaccine trial while its maker investigates whether a recipient’s “potentially unexplained” illness is a side effect of the shot.

The trial led by AstraZeneca and Oxford University was suspended while a review is underway of a participant in the United Kingdom who became ill.

HealthPartners, based in Bloomington, filled about 1,000 of its 1,500 slots in the national trial in 24 hours last week. Interest from Minnesotans helped crash the recruitment website at one point, the Star Tribune reported.

An AstraZeneca spokesperson confirmed the pause in vaccinations covers studies in the U.S. and other countries. Late last month, AstraZeneca began recruiting 30,000 people in the U.S. for its largest study of the vaccine.

Temporary holds of large medical studies aren’t unusual, and investigating any serious or unexpected reaction is a mandatory part of safety testing.

AstraZeneca pointed out that it’s possible the problem could be a coincidence as illnesses of all sorts could arise in studies of thousands of people.