U.S. company Johnson & Johnson (J&J) has paused its clinical trials for a COVID-19 vaccine candidate after a participant fell ill, just weeks after it announced that trials were in their final stage.

A pause is not entirely unexpected in vaccine trials. When another vaccine trial was temporarily stopped last month, experts hailed the move as an example of the scientific rigor that is being maintained despite the understandably intense public interest in a COVID-19 vaccine.

The Johnson & Johnson trial was paused in compliance with regulatory standards after one of its participants developed an “unexplained” illness, the company said in a news release Monday night. It said the participant’s condition was being reviewed and evaluated by the ENSEMBLE independent Data Safety Monitoring Board.

“We must respect this participant’s privacy,” the company’s statement said. “We’re also learning more about this participant’s illness, and it’s important to have all the facts before we share additional information.”

It is unclear whether the participant received the experimental vaccine or was in the placebo control group.

AstraZeneca also started its phase III trial of a vaccine candidate last month, but it was placed on pause in the U.S. after a participant in the United Kingdom was reported to have developed a spinal cord injury. The company resumed its trial with the University of Oxford in the U.K. but was awaiting approval from the Food and Drug Administration to continue in the U.S.

Dr. Francis Collins, director of the National Institutes of Health, said last month that the pause should reassure those with concerns about possible safety issues.

(SD-Agencies)