Dr. Anthony Fauci, the longtime director for the National Institute of Allergy and Infectious Diseases and emerging face of American leadership in the fight against the virus, estimated that the U.S. may see between 100,000 and 200,000 deaths from COVID-19, the deadly disease caused by the novel coronavirus. A deeply-respected authority on viral diseases, Fauci assisted in guiding the federal response to SARS, MERS, Ebola and now the novel coronavirus.

Fauci cautioned that these estimates are based on models and a model is only as accurate as the assumptions that go into building it. An extreme worst-case situation in which the coronavirus causes millions of American deaths remains “not impossible but very, very unlikely.”

“Whenever the models come in, they give a worst-case scenario and a best-case scenario,” Fauci told CNN’s Jake Tapper. “Generally, the reality is somewhere in the middle. I’ve never seen a model of the diseases that I’ve dealt with where the worst case actually came out. They always overshoot.”

Fauci believes that the U.S. is likely going to have “millions of cases” but broadly cautioned against relying on modeling estimates while still stressing the extreme risk the virus poses.