The top US infectious diseases expert is warning that distributing a Covid-19 vaccine under special emergency use guidelines before it has been proved safe and effective in large trials is a bad idea that could have a chilling effect on the testing of other vaccines.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said there are risks in rushing out a vaccine despite the urgent need.

“The one thing that you would not want to see with a vaccine is getting an EUA (emergency use authorisation) before you have a signal of efficacy,” Fauci told Reuters in a phone interview.

“One of the potential dangers if you prematurely let a vaccine out is that it would make it difficult, if not impossible, for the other vaccines to enroll people in their trial,” Fauci said.