Fauci offers an optimistic timeline for a coronavirus vaccine: a trial of 30,000 people next month, and 200 million doses by 2021

• Anthony Fauci said this week that hundreds of millions of coronavirus vaccine doses could be ready by early 2021.
• Moderna will begin testing its vaccine candidate on 30,000 people in July, Fauci said, and other companies are expected to start that final trial phase this summer as well.
• The US plans to mass-produce vaccines before knowing whether they work. Fauci still worries about how much protection they'll confer.

Pharmaceutical companies are preparing to test their coronavirus vaccines on tens of thousands of people this summer.

The fast-moving process has garnered an optimistic outlook from Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, who said on Tuesday that the US could have hundreds of millions of approved vaccines by 2021.

Moderna will begin giving its COVID-19 vaccine to 30,000 people in the first week of July, Fauci told JAMA editor Howard Bauchner in a livestreamed conversation. That's phase three of the clinical-development process — the final trial stage before a vaccine can gain approval from the US Food and Drug Administration.

In the meantime, Fauci said, the US will begin mass-producing the vaccines so it can distribute them once they gain FDA approval.

"We're going to start manufacturing doses of the vaccines way before we even know that the vaccine works," Fauci said. "We may know whether it's efficacious or not by maybe November, December. Which means that by that time, we hopefully would have close to 100 million doses. And by the beginning of 2021, we hope to have a couple of hundred million doses."

Fauci added that he was involved in at least four other vaccine trials that will start throughout the summer.

Among all these efforts, he's "cautiously optimistic" that one will produce an effective vaccine that can be distributed to the public.

"If the body is capable of making an immune response to clear the virus in natural infection, that's a pretty good proof of concept to say that you're going to make an immune response in response to a vaccine," Fauci said.

But he added: "There's never a guarantee, ever, that you're going to get an effective vaccine."

Lingering questions about immunity and vaccines

Researchers are still missing two key pieces of information about immunity to the coronavirus: whether everybody who gets infected develops immunity, and how long that protection lasts.

"I have examples of people who were clearly infected, who are antibody-negative," Fauci said, adding that those people likely have antibody counts too low for the test to detect. It's unclear if such low antibody levels are enough to protect someone from reinfection. Other recovered patients, meanwhile, show high antibody counts.

"It isn't a uniformly robust antibody response," Fauci added.

That could mean that a vaccine might not produce high levels of antibodies in some people.

For those who do gain immunity from a vaccine, it's also unclear how long that protection would last. Other coronaviruses — the kind that cause common cold — produce immunity that lasts less than a year, and in some cases just a few months.

"It may be completely different with this coronavirus," Fauci said. "We don't know."