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Dr. Deborah Birx, the response coordinator for the White House coronavirus task force, told Fox News Thursday that initial data about the coronavirus outbreak from China left U.S. officials unable to properly prepare for when the virus made its way to the U.S.

"The bottom line is we didn't know how contagious it was," Brix told Martha MacCallum during a special Fox News digital town hall event. "And I think when you make misassumptions around contagion early on, then you don't prepare in the way that you should prepare for the level of contagion that this COVID-19 exhibits."

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MacCallum had asked Birx about evidence that the Chinese deliberately downplayed the scale and virulence of the coronavirus, which originated in the city of Wuhan late last year.

Birx recounted working on countering the HIV epidemic in Africa when the virus broke out and watching COVID-19 data coming in from China.

"I think when we looked at the profile, first there was a question about human-to-human transmission -- that's really key because it stops with that first set of transmission," Dr. Birx said. "So there was that first question, and I think when you're in the midst of an epidemic, it is hard for you to be testing at a level that you need to to really look for those asymptomatic cases and really look for those people with mild disease.

"So now we're finding out that most of the reporting was around very severe cases."

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Birx added that because the early data was produced by China during a "very difficult situation" officials there were not fully measuring asymptomatic or mild cases.

"In that case," she said, "that may be a significant portion of the epidemic, and so we didn't know how it was spreading."