While he remains "cautiously optimistic" that the United States could have a Covid-19 vaccine authorized by the end of the year, the National Institutes of Health's Dr. Francis Collins warned on Friday that "it might take longer."
"I’m cautiously optimistic that by the end of 2020, there will be at least one vaccine that has reached that stage of an emergency use authorization but I don't know that for sure — and it might not happen and it might take longer," Collins, director of the NIH, said while speaking to the National Press Club in a virtual event on Friday.
Collins added that it remains "a good thing" the US has more than one vaccine candidate in development.
"It’s a good thing we have this menu of diverse scientific approaches," Collins said. "If you were betting the whole thing on one vaccine I'd be a lot more worried."
Additionally, a potential Covid-19 vaccine will need to have at least 50% effectiveness to be considered for approval by the US Food and Drug Administration, Collins said.
"FDA is not going to approve a vaccine that has less than 50% effectiveness," he added.