Don't expect a coronavirus vaccine before the election — here's the likely timeline according to doctors, government officials, and analysts

• President Donald Trump has suggested that a coronavirus vaccine may become available "right around" the US election on November 3.
• But public-health experts, financial analysts, and US government officials have said that timeline is unrealistic.
• Most experts think there's little hope of a vaccine being ready before the end of the year.
• Under the most optimistic scenario, drug companies like Pfizer and Moderna could release positive results from their human trials in October.

The answer to one of the biggest questions of the year — When will a coronavirus vaccine be ready? — differs depending on whom you ask.

Last month, the US Centers for Disease Control and Prevention told public-health officials in every state to prepare for vaccine distribution by November 1. Robert Redfield, the director of the CDC, said the goal was to get ahead of the game, since the agency expects one or more vaccines to be ready by November or December.

President Donald Trump has also suggested that a vaccine may become available "right around" the 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 on Friday. "We think we can probably have it sometime during the month of October."

But public-health experts say there's little hope of a vaccine being ready before the end of the year, let alone before the election.

On Tuesday, the CEOs of nine pharmaceutical companies issued a rare joint pledge promising to put safety before speed when developing a vaccine. The companies vowed to apply for emergency approval from the Food and Drug Administration only after demonstrating that their vaccines were safe and effective through a phase 3 trial — a vaccine's final test before it can be distributed to the public.

Under the most optimistic scenario, drug companies could release positive results from phase 3 trials in October. Pfizer and Moderna have each said that's possible.

But when it comes to rolling out that vaccine, most experts agree that it won't happen until 2021. Here's the most likely timeline according to government officials, public-health experts, and Wall Street analysts.

What government officials expect: a widely available vaccine in mid-2021

The US is lining up an army of vaccine candidates. Through Operation Warp Speed, the government is funding the manufacturing of six promising candidates in large quantities while clinical trials are ongoing. The program hopes to deliver 300 million doses of a safe, effective vaccine by January 2021.

So far, three drug companies in that program — AstraZeneca, Moderna, and Pfizer — have shown in early data that their vaccines generated immune responses without causing serious side effects. But AstraZeneca just paused its phase 3 trial over fears a UK participant may've had an adverse reaction.

Both Moderna's and Pfizer's phase 3 trials started in July, each seeking 30,000 volunteers. As of last week, Pfizer said it had enrolled 23,000 people, while Moderna had enrolled more than 21,000.

Moncef Slaoui, the chief adviser to Operation Warp Speed, told NPR last week that it was "extremely unlikely but not impossible" for those trials to finish by the end of October. A more realistic estimate, he said, is that a vaccine will become available for high-risk populations, including healthcare workers and people 70 years or older, by the end of 2020. By that time, the US could have enough capacity to immunize 20 million to 25 million people, he added.

The vaccine could then become widely available to Americans by the second quarter of 2021, Slaoui previously told Business Insider. By then, he added, the US might have already immunized about 70 million or 80 million people.

That's similar to the timeline put forward by Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases.

On Tuesday, Fauci said experts would most likely know whether a vaccine is safe and effective by the end of 2020. That could put the country on track to have tens of millions of doses available in early 2021 and hundreds of millions by the middle of the year.

Fauci added that it's "unlikely" a vaccine would be ready before the election.

At a Senate hearing Wednesday, Francis Collins, the director of the National Institutes of Health, also said he was cautiously optimistic that at least one vaccine would turn out to be safe and effective by the end of this year.

"To try to predict whether it happens on a particular week before or after a particular date in early November is well beyond anything that any scientist could tell you and be confident that they know what they're saying," Collins said.

What public-health experts think: It's unrealistic to expect results this fall

Before a vaccine can be distributed to the public, the Food and Drug Administration must issue an emergency-use authorization. EUAs require less stringent review than a full-fledged FDA approval.

FDA Commissioner Stephen Hahn told the Financial Times last month that his agency would consider issuing an EUA for a vaccine before human trials are complete if a trial showed enough positive data to prove the benefits of authorizing the vaccine outweighed the risks.

"If a vaccine is extraordinarily effective — let's say, more than 90% effective — it is possible that we would find out before all 30,000 people are enrolled in the trial," Luciana Borio, the former acting chief scientist at the FDA, recently wrote on Twitter.

But Fauci said in a recent Q&A with the Brown University School of Public Health that the chances of a vaccine being 98% effective were "not great." Scientists are hoping for a vaccine that's at least 75% effective, he added, though US regulators have said they'll authorize a vaccine that's 50% effective.

Many public-health experts are optimistic that at least one candidate will meet that standard, but they're less certain about it being ready this year.

"Early fall is unrealistic," Ashish Jha, the dean of Brown's School of Public Health, told MSNBC in July. "We just need the time to follow people to make sure they're not having adverse reactions."

Complicating the timeline further is the fact that both the Moderna and Pfizer vaccines require participants to get two shots.

Dr. Paul Offit, the director of the Vaccine Education Center at Children's Hospital of Philadelphia, told WebMD it would be "remarkable" if volunteers received their second dose in September. And after that, he said, they'd have to wait another two weeks to see whether they developed an immune response.

"I can't imagine we would have data on this by any earlier than early next year," Offit said.

Jha, similarly, told Business Insider that researchers should have "a lot more information" about a vaccine in January. He said a candidate could be ready to distribute in early 2021.

Dr. Naor Bar-Zeev, an associate professor at the Johns Hopkins Bloomberg School of Public Health, offered a less optimistic timeline to CBS Baltimore: He thinks a vaccine probably won't be widely available until the end of 2021.

What Wall Street analysts say: Pfizer and Moderna could have trial results by November

Both Moderna and Pfizer remain optimistic about their timelines.

Last week, Pfizer CEO Albert Bourla said he expected to know whether the company's vaccine worked by the end of October.

Getting results in October would be a "best-case scenario" for Moderna, the company's CEO, Stephane Bancel, recently told Business Insider. In the worst-case scenario, Moderna could be waiting until December or January.

In a research note to investors, analysts at Morgan Stanley predicted that both Moderna and Pfizer would produce trial results by mid-November. Goldman Sachs analysts, meanwhile, estimated that Moderna could know whether its vaccine candidate is effective by late November, while Pfizer's could be approved as early as October. That would put the company on track to deliver 100 million doses by the end of 2020 and 1.2 billion doses in 2021.

Analysts at Jefferies Financial Group, however, estimated that Moderna's vaccine wouldn't get emergency approval until early 2021.

It's not yet clear what effect AstraZeneca's trial pause might have on its timeline, but the SVB Leerink analyst Andrew Berens predicted Wednesday that the results could be delayed by weeks to months. The company had previously estimated that it could know whether its vaccine was effective as early as this month.

Even a widely available vaccine won't bring an instant return to normal, however. The first coronavirus vaccines might not fully prevent infection and will face enormous distribution challenges, which may mean Americans would need to continue wearing masks in public.

"I am pretty confident that we're not going to have a kind of vaccine that will somehow immediately get rid of the pandemic," Jha said. "We will have to continue to do these public health measures for a long time to come."

Andrew Dunn contributed reporting.