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Harvard Global Health Institute director Dr. Ashish Jha told "Bill Hemmer Reports" Monday that President Trump's prediction that a coronavirus vaccine would be ready by the end of this year was likely overoptimistic.

"Remember, it takes years to make vaccines in general," Dr. Jha said. "So anything that's [available in] like nine, 12, 18 months is super-fast tracked.

"The only thing I would say is we've never built a coronavirus vaccine before. This is our first time as humanity," he added. "I think we can do it, I do. All hands on deck. But we just have to plan for the possibility that it may take a little while, because we've never done this before."

"I think we're going to have a vaccine by the end of the year," Trump told Bret Baier and Martha MacCallum during Fox News' virtual town hall Sunday night, saying he was "very confident" in that assessment. "We'll have a vaccine much sooner rather than later."

"I don't mean to be the downer, obviously," Jha told Hemmer Monday. "I'm the enthusiast. I just don't want to overpromise and under-deliver. And we'd be much better if we hoped for [a vaccine in] January, but planned for June or September of 2021. And if we get a surprise, it'd be awesome."

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The doctor also had harsh words for the Centers for Disease Control and Prevention (CDC), telling Hemmer that the agency has "just been AWOL" throughout the pandemic.

"Their advice has not been on time and evidence-based, they're not giving us the data we need," Jha said. "I think we really need to take a hard look at what's happening at the CDC and why they are not performing as we expected.

"Their first [coronavirus] test failed, they've put out recommendations that have been slow, they have not been keeping up on the data. For four weeks, they took the weekend off on updating what has happening with the pandemic," he added. "You don't take weekends off in the middle of a pandemic. So there have been a lot of issues and I don't understand what's going on, but we've got to get to the bottom of it."