Anvisa, Brazil's healthcare regulator, said Wednesday that it was told a patient in a late-stage clinical trial of AstraZeneca's (AZN 0.83%) COVID-19 vaccine candidate has died. Citing medical confidentiality, it did not provide any details about the patient, the possible cause of death, and whether the patient was being administered the vaccine or a placebo. It only divulged that the patient was Brazilian.

Anvisa did say that the trial, aimed at gauging the efficacy of AZD1222, developed in coordination with the University of Oxford, would continue.

AstraZeneca has not yet responded to the regulator's announcement. A spokesperson from the university, quoted by CNBC, said that "there have been no concerns about safety of the clinical trial."

A syringe being filled with a vaccine from a vial.

Image source: Getty Images.

AZD1222 is being tested in Brazil as part of a set of clinical trials in locations around the world. The massive South American country has suffered over 154,000 coronavirus deaths, the second-highest number behind the U.S.

The announcement of the Brazil fatality comes after an AZD1222 study in the U.K. was halted in September. This occurred after one participant developed a relatively rare condition, transverse myelitis (inflammation of the spinal cord). While that trial has been resumed, late-stage testing in the U.S. is still on hold following the incident.

Prior to the U.K. trial participant falling ill, AZD1222 was considered a leading candidate in the race to get a coronavirus vaccine to market. While there are a handful of candidates undergoing late-stage testing, none has yet been approved by a major regulator for widespread use.

AstraZeneca's shares were down 1.2% on Wednesday.