Dr. Anthony Fauci told a House panel he is “cautiously optimistic” that a coronavirus vaccine will be developed this year.

“We hope that as the time we get into the late fall and early winter we will have, in fact, a vaccine that we can say would be safe and effective,” Fauci, the Director of the National Institute of Allergy and Infectious Diseases, testified before a Democrat led-panel on the outbreak on Friday, July 31. “One can never guarantee the safety or effectiveness unless you do the trial, but we are cautiously optimistic.”

Recent coronavirus vaccine trials have proved promising, with an Oxford developed vaccine triggering immune responses in early human testing. Testing out of China have also produced encouraging results. But the results do not prove the vaccine can prevent coronavirus and further trials would be needed to determine its efficacy against the fast-spreading disease.

Once developed, a vaccine would then need to be mass-produced at a scale of hundreds of millions to properly inoculate the U.S. population.

Coronavirus infections are skyrocketing in the United States, as the number of cases tops 4,400,000. With total deaths over 150,000, according to the CDC, top health experts are hoping for a vaccine to slow a potential second wave of infections in the fall.

President Trump responded to the hearings on Twitter, repeating a false claim that coronavirus cases were spiking due to an increased amount of testing in the U.S. compared to other countries. Public health experts have verified that the percentage of positive test results are rising faster than the increase in testing, proving that the virus is truly spreading.