Pharmaceutical company AstraZeneca announced Wednesday morning that its COVID-19 vaccine trial is on hold after a volunteer in the UK had an unexplained illness.

The pause includes the trial set to take place through the Indiana University School of Medicine this fall. An IU School of Medicine spokesperson said IU had not begun enrolling vaccine trial participants and no one had been given a dose of the vaccine.

In a statement, AstraZeneca said unexplained illnesses will happen by chance in all large clinical trials, and it is standard procedure for those incidents to be independently reviewed. The company did not say what the unexplained illness was, or when trials will resume.

This story was produced by Side Effects Public Media, a news collaborative covering public health.