Brazilian health authority Anvisa said on Wednesday that a volunteer in a clinical trial of the Covid-19 vaccine developed by AstraZeneca and Oxford University had died but added that the trial would continue.
Oxford confirmed the plan to keep testing, saying in a statement that after careful assessment "there have been no concerns about safety of the clinical trial."
A source familiar with the matter told Reuters that the trial would have been suspended if the volunteer who died had received the Covid-19 vaccine, suggesting the person was part of the control group that was given a meningitis vaccine.
CNN Brasil reported that the volunteer was a 28-year-old man who lived in Rio de Janeiro and died from Covid-19 complications.
Anvisa provided no further details, citing medical confidentiality of those involved in trials.
AstraZeneca declined to comment immediately.
The Federal University of Sao Paulo, which is helping coordinate phase 3 clinical trials in Brazil, separately said the volunteer was Brazilian without revealing where the person lived.
It is up to an independent review board to decide whether trials will continue, a spokesman for the university said. The board is made up of experts not from AstraZeneca, nor the universities nor the Brazilian biomedical research centre FioCruz that plans to produce the vaccine in Brazil.
So far 8,000 of the planned 10,000 volunteers in the trial have been recruited and given the first dose in six cities in Brazil, and many have already received the second shot, he said.
AstraZeneca shares fell 1.8 per cent.
Brazil's federal government has plans to purchase the UK vaccine and produce it at FioCruz in Rio de Janeiro, while a competing vaccine from China's Sinovac Biotech Ltd is being tested by Sao Paulo state's research centre Butantan Institute.
Brazil has the second deadliest outbreak of the coronavirus, with more than 154,000 killed by Covid-19, following the United States. It has the third largest number of cases, with more than 5.2 million infected, after the United States and India.