Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, testifies during the House Select Subcommittee on the Coronavirus Crisis hearing in Washington, D.C., U.S., July 31, 2020. Kevin Dietsch/Pool via REUTERS
The top U.S. 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.