WASHINGTON (NewsNation Now) — Dr. Anthony Fauci remains firm on his projection that a safe and effective coronavirus vaccine may be ready in early 2021. He acknowledged that it’s possible it could be sooner, but said it’s “unlikely.”

The White House adviser on the coronavirus told CBS This Morning, “The more likely scenario is that we will know by the end of this calendar year and hopefully we’ll be able to start vaccinations in earnest as we begin early 2021.”

Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said it’s routine for late-stage vaccine studies to be put on hold because of side effects. A study by AstraZeneca of a potential coronavirus vaccine was recently paused for safety reasons after an illness from a shot in a recipient in Britain.

He said the pause was not uncommon in vaccine development, and that he hoped the company could proceed with its trial.

“It’s really one of the safety valves that you have on clinical trials such as this,” Fauci said.

“Hopefully, they’ll work it out and be able to proceed along with the remainder of the trial but you don’t know. They need to investigate it further,” he added.

AstraZeneca didn’t reveal any information about the possible side effect except to call it “a potentially unexplained illness.” 

Fauci said people should remain vigilant about wearing masks, keeping physical distance and avoiding crowds to help prevent future surges.

The United States leads the world in coronavirus cases with 6.3 million and nearly 190,000 deaths.