Dr. Anthony Fauci says he expects to see a COVID-19 vaccine being proven safe and effective by November or December.

“I would still put my money on November/December,” Fauci said Wednesday at a Congressional Hispanic Caucus Institute panel, according to CNN.

The nation’s top infectious disease expert has said that researchers test vaccines by giving the shots to some and a placebo to others, then waiting to see if those who got the actual vaccine develop fewer cases or less-severe symptoms.

He said that to tell if a vaccine candidate is effective, researchers need to see about 150 coronavirus infections occur.

Depending on when those metrics come, Fauci said there could be a solution to the pandemic sooner than his predicted time frame.

“It really depends on where the sites are and how many infections there are in a site,” Fauci said. “So you could get your answer sooner, or you can get your answer a bit later.”