NEW YORK/CHICAGO/ U.S. President Donald Trump has said a vaccine for the novel coronavirus could be available before the Nov. 3 presidential election, sooner than most experts anticipate.

FILE PHOTO: A small bottle labeled with a "Vaccine" sticker is held near a medical syringe in front of displayed "Coronavirus COVID-19" words in this illustration taken April 10, 2020. REUTERS/Dado Ruvic/Illustration

A COVID-19 vaccine as early as October could become a reality if drugmakers deliver on optimistic timelines for completing large, late-stage clinical trials and regulators allow for its use prior to a full review and approval.

The U.S. Food and Drug Administration can greenlight medical products during public health emergencies by issuing an emergency use authorization (EUA) before all the data are in to complete a formal review.

The FDA has issued EUAs for many COVID-19 tests and for a few treatments. On Sunday, the FDA authorized on an emergency basis the use blood plasma from recovered COVID-19 patients as a treatment. The FDA commissioner later corrected data he cited at a news conference that significantly overstated the treatment’s known ability to save lives.

EUA’s are not typically used for vaccines intended for healthy people to prevent infection. That presents a higher bar for approval than treatments for people with life-threatening disease.

Nevertheless, the FDA in June released EUA guidance for COVID-19 vaccines. Once it grants an EUA, the agency eventually must issue a formal marketing approval or revoke emergency authorization.

HOW MUCH TIME COULD AN EUA SAVE?

Typical FDA approval reviews take eight months or longer, with a priority review shaving off a couple of months. But the agency has moved quickly during past public health crises. During the 2009 H1N1 swine flu pandemic, it only took two months to get an approved vaccine, but those were based on existing seasonal flu vaccines.

An EUA for a vaccine using a new approach might only save a few weeks, some experts say. The FDA would still need substantial data, said Dr. Kathryn Edwards, former chairwoman of the FDA’s vaccine advisory committee and scientific director at the Vanderbilt Vaccine Research Program.

“What they do seem to be telling us is that once you show that your vaccine works ... that might be a time when an EUA may be used” before the paperwork is completed, said Filip Dubovsky, chief medical officer of vaccine maker Novavax Inc (NVAX.O).

IS IT RISKY TO USE AN EUA FOR VACCINES?

The U.S. government decided against an EUA for the H1N1 vaccine after a survey found 64% of Americans would not take it if it had not gone through the formal approval process.

Consumer rights watchdog Public Citizen urged regulators not to use an EUA for COVID-19 vaccines, which it says could create the appearance of a rushed review.

The FDA and other U.S. health experts say there must be sufficient safety and efficacy data before a vaccine is authorized for public use.

“I certainly would not recommend nor would I ever allow myself to be injected with a vaccine that has not been thoroughly vetted and approved by the FDA,” said former FDA associate commissioner Dr. Peter Pitts, president of the Center for Medicine in the Public Interest.

COULD TRUMP PRESSURE THE FDA TO ISSUE AN EUA WITHOUT SUFFICIENT DATA?

Trump, without citing evidence, on Saturday accused “deep state” elements in the FDA of holding up vaccines and treatments in order to undermine his reelection prospects.

FDA Commissioner Stephan Hahn has denied that assertion. Peter Marks, one of the FDA’s top drug reviewers, told Reuters he would resign if he felt the agency was pressured to approve a vaccine before it was ready.

Dr. Jesse Goodman of Georgetown University, a former FDA chief scientist, said a vaccine EUA could undermine public confidence in the agency. He cited pressure around hydroxychloroquine, a treatment pushed by Trump and others in his administration, which received an EUA that was later revoked when data showed a lack of efficacy and safety issues.

“We’re certainly seeing a situation where norms are not being respected government-wide,” Goodman said.

WHICH DRUGMAKERS HAVE A SHOT AT A VIABLE VACCINE BEFORE THE ELECTION?

AstraZeneca Plc (AZN.L) in conjunction with Oxford University researchers and Pfizer Inc (PFE.N) with partner BioNTech SE (22UAy.F) have said they could have pivotal data by October. Moderna Inc (MRNA.O) is not far behind with late-stage data expected as soon as November or December.