Albert Bourla, Pfizer's CEO, said it's not clear if the company's coronavirus vaccine will no longer be able to spread the virus to other people.
Bourla told NBC's "Dateline": "I think this is something that needs to be examined. We are not certain about that right now with what we know."
Independent researchers have already made it clear that the trials used to test the vaccine did not examine its effects on transmission.
Business Insider reports the US could approve Pfizer's vaccine on December 10.