“I don’t think proving this in an animal model is on the critical path to getting this to a clinical trial,” said Tal Zaks, chief medical officer at Moderna, a Cambridge, Mass.-based biotech that has produced a Covid-19 vaccine candidate at record speed. He told STAT that scientists at the National Institutes of Health are “working on nonclinical research in parallel.” Meanwhile, the clinical trial started recruiting healthy participants in the first week of March.

“That isn’t how vaccine testing normally happens. Regulators require that a manufacturer show a product is safe before it goes into people, and while it isn’t enshrined in law, researchers almost always check that a new concoction is effective in lab animals before putting human volunteers at potential risk.”