CDC director Robert Redfield just told Senators that most Americans won't get a coronavirus vaccine until summer or fall 2021

• At a Senate subcommittee hearing on Wednesday, CDC Director Robert Redfield said most Americans won't receive a coronavirus vaccine until "late second quarter, third quarter 2021." 
• That contradicts the timeline that Paul Mango, deputy chief of staff for policy at the Department of Health and Human Services, put forward the same day.
• Mango said the US is on track to "vaccinate every American before the end of first quarter 2021." 
• Most experts agree that a vaccine won't be available before the election this fall.
• Visit Business Insider's homepage for more stories.

Don't hold your breath for a coronavirus vaccine this fall. 

That's the resounding refrain from US public-health officials, including Robert Redfield, director of the Centers for Disease Control and Prevention. At a Senate subcommittee hearing on Wednesday, Redfield said a vaccine won't be widely available to the American public until the summer or early fall of 2021.

"There will be vaccine that will initially be available sometime between November and December, but very limited supply and will have to be prioritized," Redfield said Wednesday. "If you're asking me when is it going to be generally available to the American public so we can begin to take advantage of vaccine to get back to our regular life, I think we're probably looking at late second quarter, third quarter 2021." 

Under the most optimistic vaccine timeline, leading drug companies could see promising results from their clinical trials this fall or by the end of the year. Pfizer and Moderna, in particular, could release results from their phase 3 trials in October. The AstraZeneca-Oxford phase 3 trial could also yield results by the end of 2020, even though that trial was paused briefly after a participant had an adverse reaction.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said experts probably won't know whether a vaccine is safe and effective until the end of 2020.

But even once a vaccine is proven safe and effective, the US won't immunize everyone right away. Instead, priority will go to high-risk populations such as healthcare workers and people 70 years or older.

The US government is funding the research, development, and manufacturing of six vaccine candidates through a program called Operation Warp Speed. The chief adviser to that program, Moncef Slaoui, previously told Business Insider that the US might be able to immunize about 70 million or 80 million people by the second quarter of 2021.

But Paul Mango, the deputy chief of staff for policy at the Department of Health and Human Services, has put forward a speedier timeline. 

During a Wednesday press call, Mango said the US was on track to "vaccinate every American before the end of first quarter 2021." He added that the Food and Drug Administration would likely grant emergency authorization for a coronavirus vaccine by the end of 2020. 

That's not impossible, but many public-health experts say it's unlikely. 

Even less likely is President Donald Trump's suggestion that that a vaccine may become available "right around" the presidential election on November 3.

"We remain on track to deliver a vaccine before the end of the year and maybe even before November 1," Trump said during a White House news conference earlier this month "We think we can probably have it sometime during the month of October."

Regardless of when the first doses of a vaccine become available, public-health experts will likely continue to recommend face masks for the American public well into next year. At the Senate hearing on Wednesday, Redfield even said face masks may offer a better guarantee of individual protection from COVID-19 than an early vaccine. That's because the FDA has said it will authorize a vaccine if it's at least 50% more effective than a placebo at preventing or reducing the severity of the disease — so it wouldn't eliminate your risk of getting a coronavirus infection.

"If I don't get an immune response, the vaccine's not going to protect me," Redfield said. "This face mask will."