Tom's next guest is Dr. Gigi Gronvall, an immunologist and senior scholar with The Johns Hopkins Center for Health Security, part of the Bloomberg School of Public Health.

She joins us to discuss what we know - and what we still need to know - about the origins of the SARS CoV-2 virus. What is the evidence that the virus originated in a lab, instead of passing to humans through animals? And what will it take for scientists to come to a definitive conclusion?

Dr. Gronvall has been studying and writing about a number of issues related to the COVID 19 pandemic for these last many months.

Dr. Gigi Gronvall joins us from her home in Baltimore.