The University of Oxford has said a trial of its coronavirus vaccine will continue in Brazil amid reports of the death of a volunteer.
Oxford is in advanced stages of testing a Covid-19 immunisation being developed with AstraZeneca, with volunteers in countries including Brazil, the UK and the US.
The university said it had investigated the case but found "no concerns about safety" around the vaccine.
Oxford said in a statement: "All significant medical incidents, whether participants are in the control group or the Covid-19 vaccine group, are independently reviewed.
"Following careful assessment of this case in Brazil, there have been no concerns about safety of the clinical trial and the independent review in addition to the Brazilian regulator have recommended that the trial should continue."
Brazil's health authority said it was informed of the death of a participant earlier this week.
AstraZeneca said it could not comment on individual cases due to patient confidentiality, but said all due processes had been followed and there were no issues with the trial continuing.
A spokesperson said: "All significant medical events are carefully assessed by trial investigators, an independent safety monitoring committee and the regulatory authorities.
"These assessments have not led to any concerns about continuation of the ongoing study."
According to local media reports, the volunteer had been given a placebo jab rather than the vaccine.
Experts in the UK said since it appeared the volunteer's death was not vaccine-related, there was no reason the trials should be stopped.
"Without details it's impossible to know what has happened in this case but as the trial is continuing, I think we can assume the circumstances of the death were such that it was clearly not vaccine related," Ian Jones, Professor of Virology at the University of Reading, said in a statement issued by independent science publicity group the Science Media Centre.
"What we have to remember is that in any large trial the normal processes of morbidity and mortality are still operating and that sometimes an event will occur in a trial participant which would have occurred anyway, trial or not.
"The case will have been carefully examined and, as vaccine relatedness has presumably been ruled out, the trial should continue to bring the vaccine to a decision point as soon as possible."
University of Edinburgh Professor of Immunology and Infectious Disease Eleanor Riley said: "Every reputable clinical trial, such as this trial being undertaken by the Oxford/Astra Zeneca partnership, is overseen by an independent data and safety monitoring board.
"This board will have reviewed the case in detail before reviewing the data in detail before liaising with the Brazilian and international regulators before determining that the trial can continue."
Andrew Freedman, Reader in Infectious Diseases and Honorary Consultant Physician at the Cardiff University School of Medicine, said: "Fortunately, deaths resulting from the administration of a trial drug or vaccine are very rare and would normally lead to the immediate discontinuation of the trial."