Updated

White House coronavirus task force member Dr. Anthony Fauci told "Special Report" Monday that researchers should know the efficacy of a potential coronavirus vaccine produced by biotech company Moderna by "mid-to-late fall."

The Massachusetts-based company began dosing participants in its Phase III clinical trial Monday morning.

"We're going to have 30,000 people in the trial, 15,000 will get the vaccine, 15,000 will be [given] placebo," Fauci told host John Roberts. "If you look at the accrual and the rate of accrual ... you could project that you’ll get an answer sometime in the mid-to-late fall, that would be November, that could be October.

"It's very difficult to predict."

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Fauci, the director of the National Institute of Allergy and Infectious Diseases, insisted that "there are no corners being cut" in the hunt for a coronavirus vaccine in response to claims that President Trump has presssed for a vaccine to be available before the November election.

"Safety is very important and what we are doing is not compromising safety and certainly not compromising scientific integrity," Fauci said. "We, in fact, briefed the president today about this in the Oval Office and there's no political pressure that I have seen at all to move quickly. The speed of the trial and how quickly you get the results is dependent upon certain factors. One is the number of infections that you get within the context of the trial to determine if it works or not."

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The Moderna vaccine candidate directs the body’s cells to express the SARS-CoV-2 spike protein to elicit a broad immune response. Fauci said results from early-stage clinical testing, that showed the vaccine candidate to be safe and producing an immune response, left him "cautiously optimistic that we may have something here, but it’s gonna take a few months to determine whether or not we do."

"Hopefully within a period of a few months, we will be able to get a signal to know whether it actually is effective in preventing infection with the coronavirus," he added.

The vaccine efficacy trial is said to be the first implemented under Operation Warp Speed, a multiagency collaboration led by the Department of Health and Human Services that aims to speed along the development, manufacturing and distribution of medical countermeasures for COVID-19.

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"It's an extraordinary circumstance, " Fauci said of the accelerated vaccine hunt, for which he credited improvements in technology that have "really been transforming the way we do vaccine trials."

"This is the fastest we have ever gone," he told Roberts, "from the identification of a new virus and doing the sequence, getting the vaccine, and going into Phase III trial for efficacy."

Fox News' Kayla Rivas contributed to this report.