Transcript for CDC director responds to Trump’s COVID-19 vaccine timeline
We're going to turn now to the coronavirus here in the U.S., and president trump moments ago contradicting the CDC director, Dr. Robert Redfield, who spoke today about an initial vaccine here in the U.S. And on timing, saying most Americans likely won't get the vaccine until well into next year. Just before we came on the air tonight, the president said the director was confused today. The president offering his own timing. And there's news coming in tonight on another positive case of the virus inside the white house. Here's Mary Bruce. Reporter: Tonight, with the election fast approaching, president trump wants Americans to know a vaccine is coming soon. His administration announcing that as soon is one is approved, they'll start shipping doses within 24 hours. We think we can start sometime in October. So, as soon as it's announced, we'll be able to start. Reporter: But on capitol hill, the head of the CDC said that while a limited supply may be available in November or December, most Americans will have to wait much longer than that. When is it going to be generally available to the American public? So we can begin to take advantage of vaccine to get back to our regular life, I think we're probably looking at third -- late second quarter, third quarter 2021. Reporter: But late today the president bluntly rejecting that scientific assessment. I think he made a mistake when he said that. It's just incorrect information. I believe he was confused. Reporter: Joe Biden today with a warning. We can't allow politics to interfere with a vaccine in any way. So let me be clear. I trust vaccines. I trust scientists. But I don't trust Donald Trump. Reporter: We pressed him on the message he's sending to Americans. Is there a risk that that message, that questioning the president on a vaccine, could prevent people from trusting the science, from the u.s.ing a vaccine when there finally is No, because they know he doesn't have any respect for there has to be total transparency so scientists outside the government know exactly what is being approved. The context in which it's being approved, and why it's being approved. Reporter: For a vaccine to work though, to be effective, you do need a certain amount of the population to be willing to take it. That's right. Reporter: You're -- you're saying, "Don't trust the president, trust me if I'm elected." Are you confident that enough Americans will buy in? No, I'm not. I'm saying trust the scientists. Reporter: And if the scientists say a vaccine under the president's watch is safe and effective, take it? Absolutely. Do it. Reporter: Biden also took aim at the president's comments in the ABC news town hall. The president still refusing to urge Americans to wear a mask. There are a lot of people who think the masks are not good, and there are a lot of people that, as an example, you have -- Who are those people? I'll tell you who those people are, waiters. They come over and they serve you, and they have a mask, and I saw it the other day, where they were serving me and they're playing with a mask. I'm not blaming them. I'm just saying what happens. They're playing with a mask, so the mask is over and they're touching it and then they're touching the plate and -- that can't be good. There are people that don't think masks are good. Reporter: But today, the CDC director made clear masks are good and necessary. Face masks are the most important public health tool we have. I might even go so far as to say that this face mask is more guaranteed to protect me against covid than when I take a covid vaccine. Directly contradicting the president last night in our town hall. Mary Bruce in Wilmington, Delaware. And Mary, president trump moments ago reacted to the words of Dr. Redfield today, saying he is wrong on masks, wrong on a vaccine distribution timeline, but to clear here, for folks at home, most public health experts agree with Dr. Redfield on this? Reporter: They do. But despite the fact that top scientists back up Redfield, the president is completely undermining him. We can't stress enough, this is just an extraordinary clash between the president and his own CDC director, right in the middle of a pandemic and with just 48 days until the election. And Mary, before you go, the president just now confirming another member of the white house staff has tested positive for coronavirus? Reporter: He did, but the president provided very few details. We do not know who this staffer is, but the president said it's not someone who he's been associated with. David? Mary Bruce tonight.
This transcript has been automatically generated and may not be 100% accurate.