White House chief of staff Mark Meadows expressed confidence in the progress being made on a coronavirus vaccine, saying Wednesday he believes one could be ready as soon as this fall.

Several vaccine candidates have been going through trials at a rapid pace as part of President Trump's Operation Warp Speed, in which the federal government and private sector companies are teaming up with the goal of putting an end to COVID-19.

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"I'm optimistic that we'll have a vaccine by the fall," Meadows told Politico Playbook after being asked about a New York Times report that said the government could issue an emergency use memo for a vaccine. AstraZeneca is one company that has recently been reported to have made strides in its efforts to develop and produce a vaccine, but Meadows said there are others as well.

"There are a number of vaccines that are in phase 3 clinical trials," he said. "What we are doing is trying to produce all the candidates, produce hundreds of millions of vials of the vaccine so whether it is actually AstraZeneca or any of the others that are out there that get approved we’re going to make sure it’s good science and the efficacy and the safety of those vaccines are well tried. It is warp speed but I’m optimistic that one of the seven or eight candidates that we have will actually get approved and hopefully be able to be deployed by this fall.”

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Meadows was asked whether the U.S. would accept vaccine trials from other countries, as Russia has recently announced it has developed a vaccine. Meadows was clear that the answer is no.

"We're not going to accept a foreign trial from Russia," Meadows said, laughing. "Listen, any trial that we have, we have FDA protocols that we're going to follow, we're going to continue to follow those. I think I've made it very clear on that. Obviously we have the highest health and safety standards in the world. That's not something you can sacrifice. You can cut the red tape but you can't cut corners. And so the Russia trial, I wouldn't take that vaccine."

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Meadows also spoke about the long-awaited next coronavirus stimulus package, which has stalled in Congress. Meadows said he has not had any recent talks with House Speaker Nancy Pelosi, D-Calif., or Senate Minority Leader Chuck Schumer, D-N.Y., but he said he has daily talks with Republican senators who he said want a deal and "are willing to make compromises."