The top executives of nine drugmakers likely to produce the first vaccines against the new coronavirus signed an unprecedented pledge meant to boost public confidence in any approved vaccines.

The companies said today that they will stick to the highest ethical and scientific standards in testing and manufacturing and will make the well-being of those getting vaccinated their top priority.

The announcement comes amid worries that President Donald Trump will pressure the U.S. Food and Drug Administration to approve a vaccine before it’s proven to be safe and effective.

The president has repeatedly said a vaccine could be ready by the end of the year, or even as early as October. His administration also is pressing ahead with what it calls “Operation Warp Speed,” a program meant to accelerate the development and manufacture of vaccines.

Meanwhile, public health officials have expressed doubt that adequate data on vaccine safety and effectiveness would be available before November. They also worry if Americans stay away from the vaccine because they don’t trust it, COVID-19 will be harder to control.

The pledge announced today was signed by the chief executive officers of American drugmakers Johnson & Johnson, Merck, Moderna, Novavax and Pfizer, and European companies AstraZeneca, BioNTech, GlaxoSmithKline and Sanofi. BioNTech has partnered with Pfizer on one of the three vaccines now in the final round of human testing.

The companies said they will seek approval or authorization for emergency use only after they have confirmed the vaccines work and are safe through a large, final round of human testing.

“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 pledge states.

The CEOs also promised to “ensure a sufficient supply and range of vaccine options, including those suitable for global access.” The statement noted the nine companies previously created more than 70 new vaccines against deadly diseases, helping to eradicate some of them.

The executives likely worry that skepticism about the their medicines could limit sales, given an AP-NORC poll in May found that only about half of those surveyed planned to get the vaccine. The country already has a small, but vocal, group of “anti-vaxxers” who oppose giving their children the many standard vaccines.

The FDA’s credibility also has been shaken by its emergency authorizations — at the urging of the Trump administration — for two unproven treatments, convalescent plasma and malaria drug hydroxychloroquine. Both were heavily criticized by many medical experts.

Last week, the Merck and Pfizer CEOs joined chief executives of three other companies that are testing COVID-19 drugs and vaccines to pledge that they won’t seek even emergency approval without solid results in final stage human testing. They added that extra transparency on testing results and the approval process is needed.

Meanwhile, the international Biotech Innovation Organization also released a letter urging scientists to follow several principles to ensure any COVID products approved work and are safe. Those include calls for testing results to be disclosed via scientific meetings and medical journals, not press releases, and for the FDA to “maintain its historic independence as the gold-standard international regulatory body, free from external influence.”