WHO conditionally backs Covid-19 vaccine trials that infect people

Challenge' studies would deliberately give coronavirus to healthy volunteers

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Controversial trials in which volunteers are intentionally infected with Covid-19 could accelerate vaccine development, according to the World Health Organization, which has released new guidance on how the approach could be ethically justified despite the potential dangers for participants.

So-called challenge trials are a mainstream approach in vaccine development and have been used in malaria, typhoid and flu, but there are treatments available for these diseases if a volunteer becomes severely ill. For Covid-19, a safe dose of the virus has not been established and there are no failsafe treatments if things go wrong.