The chief executives of nine drug companies pledged Tuesday not to seek regulatory approval before the safety and efficacy of their experimental coronavirus vaccines have been established in Phase 3 clinical trials, an extraordinary effort to bolster public faith in a vaccine amid President Trump’s rush to introduce one before Election Day.

“We believe this pledge will help ensure public confidence in the rigorous scientific and regulatory process by which covid-19 vaccines are evaluated and may ultimately be approved,” the executives wrote in their joint statement. The Wall Street Journal first reported Friday that a statement from the companies would be forthcoming.

The statement included a vow that the companies would “only submit for approval or emergency use authorization after demonstrating safety and efficacy through a Phase 3 clinical study that is designed and conducted to meet requirements of expert regulatory authorities such as FDA.”

They also vowed to “always make the safety and well-being of vaccinated individuals our top priority.”

The statement left open the door for the use of partial data from the massive Phase 3 vaccine trials — which require the participation of at least 30,000 test subjects — to seek emergency-use authorization. Such trials typically take years to complete and require lengthy follow-up to see how long protection from a vaccine may last.

The executives signing the pledge included the leaders of AstraZeneca, Johnson & Johnson, Merck, Moderna, and Novavax, as well as those heading two joint vaccine projects, Pfizer and BioNTech, and Sanofi and GlaxoSmithKline.

The United States began Phase 3, one of the last steps in developing a vaccine, on July 27, 2020. We take you inside the process. (The Washington Post)

On Tuesday, AstraZeneca announced that human tests of a coronavirus vaccine being developed in collaboration with the University of Oxford have been put on hold pending a review of safety data triggered by a “potentially unexplained illness.”

In most contexts, pledges by drug companies that they will adhere to safety and efficacy standards would be unremarkable. But their joint resolve in the current political environment — and the headline pasted on their statement: “BIOPHARMA LEADERS UNITE TO STAND WITH SCIENCE” — make clear their intent to ease growing worries about the race for a vaccine amid intense White House pressure.

Trump has increasingly tied his reelection hopes to introduction of a vaccine before Nov. 3. The White House said in a statement Monday that Trump has no intention of cutting corners.

“The American people can rest assured that any approval will maintain the FDA’s gold standard for safety and testing to ensure a vaccine or therapeutic is effective,” White House spokesman Judd Deere said in an email. “This false narrative that the media and now the Democratic nominee for vice president [Sen. Kamala D. Harris] are suggesting that politics is influencing approvals is not only false but is a danger to the American public.”

Harris (D-Calif.) said Sunday on CNN’s “State of the Union” that she would “not take [Trump’s] word for it” and would “not trust” his declarations about the safety of a vaccine.

Vaccine manufacturers want to bolster public faith in the safety and efficacy of a vaccine to counter perceptions that the Food and Drug Administration will cave to political pressure, said Amesh Adalja, senior scholar at the Johns Hopkins University Center for Health Security.

“It just reflects the fact that we have seen political meddling from the start in this pandemic response,” Adalja said.

He cited the FDA’s hasty emergency-use authorization of hydroxychloroquine to treat the novel coronavirus. That authorization was withdrawn in June after clinical trials showed hydroxychloroquine provided no benefit while potentially increasing risks of fatal heart arrhythmia, as well as the botched rollout of last month’s emergency-use authorization for convalescent plasma, when FDA Commissioner Stephen Hahn overstated potential benefits of the transfusions.

Convincing the public that a vaccine is safe and effective will be vital to making sure enough of the population gets immunized against SARS-CoV-2 to stem the tide of the pandemic, Adalja added.

“There is a thriving anti-vaccine movement that will use any kind of misstep when it comes to vaccine safety to undermine confidence in all vaccines,” he said.

The drug executives’ statement Tuesday emphasized that the FDA has established a rigorous set of rules for evaluating vaccines.

“FDA’s guidance and criteria are based on the scientific and medical principles necessary to clearly demonstrate the safety and efficacy of potential covid-19 vaccines,” they said. “More specifically, the agency requires that scientific evidence for regulatory approval must come from large, high quality clinical trials that are randomized and observer-blinded, with an expectation of appropriately designed studies with significant numbers of participants across diverse populations.”

The companies also stated they collectively have previous experience creating 70 successful vaccines “that have helped to eradicate some of the world’s most complex and deadly public health threats.”

Trump’s own top vaccine adviser, Operation Warp Speed co-chief Moncef Slaoui, said in an interview on NPR last week that it is “very unlikely” a vaccine would be authorized before Election Day. Slaoui was responding to reports that the Trump administration had told states to prepare to distribute vaccine by Nov. 1, two days before the election.

“There is a very, very low chance that the trials that are running as we speak could [be completed] before the end of October and therefore there could be — if all other conditions required for an Emergency Use Authorization are met — an approval,” Slaoui told NPR. “I think it’s extremely unlikely but not impossible, and therefore it’s the right thing to do to be prepared, in case.”

Slaoui said in a separate interview with the news site Science that he would not remain in the administration if he detected “undue” political pressure in vaccine approval.

“I would immediately resign if there is undue interference in this process,” he said, adding: “I have to say there has been absolutely no interference.”