Brazilian regulator says testing of the vaccine will, however, continue even after the volunteer's death. We send a lot of doctors, nurses and care workers to work every day, and some will get really sick and die of COVID-19 in the next few weeks.
None of the current trials are created to detect a reduction in any serious outcome such as hospitalizations, intensive care use, or deaths.
The D'Or Teaching and Research Institute (IDOR), which is helping organize the tests in Brazil, said the independent review had "raised no doubts about the safety of the study, and recommended it continue".
As the prevalence of COVID-19 rises and falls in populations, it can make it hard for traditional vaccine trials to assess if vaccines work, because volunteers receiving the vaccine may not be naturally exposed to the virus. Still, a vaccine that can reduce symptomatic COVID-19 in healthy adults is essential, as it will reduce the risk of infection of vulnerable groups.
Aside from all the clinical work that goes into the development of a vaccine, real-world human trials are slow.
Brazil has had almost 5.3 million confirmed coronavirus cases - the third highest tally in the world after the USA and India - and is second only to the U.S. in terms of deaths, with almost 155,000 registered so far, according to data collated by Johns Hopkins University. "Current trials are not created to tell us" by Peter Doshi, 22 October 2020, The BMJ. It could not confirm that the letter had been issued.
"We also can not comment on a pending FDA decision", she said.
AstraZeneca did not immediately reply to a request for comment.
Trials resumed after British regulators and an independent review concluded the illness was not a side effect of the vaccine.
"Hospitalisations and deaths from covid-19 are simply too uncommon in the population being studied for an effective vaccine to demonstrate statistically significant differences in a trial of 30,000 people", he adds.
Chris Chiu, a scientist at Imperial College London co-leading the COVID-19 challenge experiments, said the plan was to give remdesivir to infected volunteers based on a "strong belief" it will be effective if given in the very earliest stages of disease.
Other viruses including those that cause West Nile and polio can trigger the condition, as can physical trauma. The person's death has apparently occurred as a result of "complications from COVID-19", the Globa newspaper reported. "That's always the line that you walk".