Dr. Scott Gottlieb told CNBC on Monday that the late-stage coronavirus vaccine trials underway in the U.S. are unlikely to have gathered enough evidence to receive emergency approval ahead of the November presidential election.
"I think it's very unlikely. I think it's more likely you're going to get a top-line result some point in November and maybe be able to make a decision about an emergency use authorization after that," the former Food and Drug Administration commissioner said on "Squawk Box."
Gottlieb — who sits on the board of Pfizer, which is developing a vaccine to prevent Covid-19 — said the more effective the vaccine is, the sooner the trial is likely to generate data on effectiveness.
"If the vaccines are very effective at preventing Covid disease, probably 70% to 80% effective based on how the trials are powered, you could get a readout at some point in October, a sort of top-line readout," he said. "But it's more likely that you're going to get a readout from those trials in November."
Gottlieb said the only circumstance in which a vaccine trial could offer sufficient effectiveness data in October would be if the U.S. coronavirus outbreak is "very dense," meaning there is high transmission rates throughout the general population, and the vaccines prove to be "very effective" in those in trials.
"But that probably wouldn't leave enough time to issue an emergency use authorization by November, regardless," said Gottlieb, who led the FDA in the Trump administration from May 2017 to April 2019.
Gottlieb's comments Monday came after the current FDA chief, Dr. Stephen Hahn, indicated the public health agency could issue emergency authorization for a vaccine before phase three clinical trials are completed if the benefits outweigh the risks.
"It is up to the [vaccine developer] to apply for authorization or approval, and we make an adjudication of their application," Hahn said in an interview with the Financial Times. "If they do that before the end of phase three, we may find that appropriate. We may find that inappropriate, we will make a determination."
Gottlieb, who preceded Hahn at the FDA, said he was not exactly sure what Hahn's comments meant.
"It's possible what Dr. Hahn was referring to was issuing an emergency use authorization before the trials are fully complete, insofar as these are two-year trials. There's going to be a two-year period of safety follow up on these clinical trials," Gottlieb said.
"It's likely to be the case that there's going to be an emergency use authorization if these vaccines are otherwise safe and effective for some select, high-risk populations like perhaps front-line health-care workers or people who have infirmities, elderly patients in nursing homes who are at higher risk of a bad outcome," Gottlieb added. "That might be what he meant by saying they might issue an emergency use authorization before the trials are quote-unquote complete."
President Donald Trump has embarked on an effort to accelerate vaccine development in the U.S. called Operation Warp Speed, which aims to provide at least 300 million doses of a coronavirus vaccine by January 2021.
Last week, at the Republican National Convention, Trump said the U.S. "will produce a vaccine before the end of the year, or maybe even sooner," setting off concerns again that the approval process could be influenced by political considerations instead of health and science.
Earlier this month, Trump was asked in a radio interview whether a vaccine could be ready before Nov. 3, the date of the presidential election. "I think in some cases, it's possible before but right around that time," he said in response.
Developing a safe and effective vaccine to prevent a disease is a process that usually takes years. But scientists in the U.S. and around the globe are working with intensified urgency to come up with a vaccine to slow the transmission of the coronavirus, which has infected more than 25 million people worldwide and killed nearly 847,000 since it was first discovered in Wuhan, China, late last year. The pandemic also has had devastating economic consequences.
Multiple companies, including Pfizer and Moderna, are in late-stage human trials, with thousands of people receiving vaccines as part of the scientific studies. Johnson & Johnson plans to begin its phase three trial, potentially enrolling up 60,000 people, in September.
In his FT interview, Hahn stressed the FDA's decision-making process for approving a coronavirus vaccine would be above political considerations. Despite the pandemic converging with an election, Hahn said the agency would "stick to our core principles." He stressed: "This is going to be a science, medicine, data decision. This is not going to be a political decision."
Gottlieb said the process to approve a vaccine "has a lot of integrity to it," expressing confidence in the longtime scientists at the FDA.
"This is process where you have multiple layers of scientific review. You have objective criteria that the agency has issued in the form of guidance documents that lay out what the approvable endpoints are for these clinical trials, and what kind of safety they want to make a preliminary read on whether or not these vaccines are safe," he said. "The final signoff is a career head of the biologics center at FDA who is exceptional."
"I think if the commissioner would trust the process and elevate that process, people would have confidence in what's unfolding inside the agency," Gottlieb added.
Disclosure: Scott Gottlieb is a CNBC contributor and is a member of the boards of Pfizer, genetic-testing start-up Tempus and biotech company Illumina. He also serves as co-chair of Norwegian Cruise Line Holdings' and Royal Caribbean's "Healthy Sail Panel."