It could be days before the 77-year-old Biden will be in the clear, despite recent negative tests. The virus can incubate for up to 14 days.

Donald Trump was quite likely infectious at the Tuesday debate, medical professionals say, considering the severity of the symptoms on Friday, in which he necessitated oxygen before being transported to Walter Reed Military Medical Center.

“A person is at their peak infectiousness in the 48-hour period before they start showing symptoms,” said Leana Wen, a former health commissioner for Baltimore and ER physician. “If that timeline is correct, then [Trump] would actually be at the peak of contagion on Tuesday night.”