Stephen M. Hahn, a physician, is commissioner of the Food and Drug Administration.

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Since the outbreak of the covid-19 pandemic, developing a safe and effective vaccine has been an urgent worldwide priority: to save lives, and to bolster the public’s confidence in returning to a semblance of normal life.

At the Food and Drug Administration and our parent agency, the Department of Health and Human Services, we recognize the vital importance of vaccine development. The framework in the United States to support a covid-19 vaccine is now in place. Testing is underway and manufacturing capacity is rapidly expanding. But let’s be clear: The development effort must adhere to standards that will ensure any covid-19 vaccine’s safety and effectiveness.

Large-scale clinical trials already have begun for several promising vaccine candidates. The data from these trials will enable the scientists at the FDA to determine which of these candidates has the greatest potential to provide protection from the virus, what the possible side effects are and how long immunity is likely to last. FDA scientists will need the information to decide whether approval of the vaccine for general use is justified. This fall, we expect to start identifying which vaccine candidates are truly viable.

At the same time, our colleagues at Operation Warp Speed, which operates independently of the FDA as a partnership between HHS and the Defense Department, have been arranging for the stockpiling of vials and other equipment needed for a national immunization program.

Success will hinge, of course, on the data that emerges from clinical trials. This testing by its very nature takes time: It takes time for the human body to develop immunity, and it often takes time for side effects to emerge. While speed is essential in this global emergency, we at the FDA are committed to maintaining strict scientific principles and protection of those who volunteer as vaccine test subjects.

To prepare for the completion of tests and data submission, our agency has announced that any authorized or approved covid-19 vaccine would need to show that it prevents the disease or decreases its severity in at least 50 percent of people who are vaccinated. This is a reasonable standard given the nature and impact of the pandemic.

One key element in the FDA’s testing requirements is assuring diversity among the test subjects. All phases of vaccine clinical development should include the people most affected thus far by covid-19, specifically racial and ethnic minorities, elderly individuals, and people with other medical conditions. Only by gathering data on these populations can we gain a full understanding of a vaccine candidate’s safety and effectiveness.

I have been asked repeatedly whether there has been any inappropriate pressure on the FDA to make decisions that are not based on good data and good science. I have repeatedly said that all FDA decisions have been, and will continue to be, based solely on good science and data. The public can count on that commitment.

Once FDA scientists determine that a covid-19 vaccine candidate meets the appropriate regulatory standards for safety and efficacy, a pathway will be created by the government to make the vaccine available without delay. And, of course, after authorization or approval by the FDA, the safety of any vaccine will be closely monitored.

Since we at the FDA are the final arbiters of whether a particular vaccine is safe and effective, I cannot make any predictions about timing of an emergency use or final approval of a covid-19 vaccine. But I can attest that every FDA resource has been, and will continue to be, at the ready to facilitate clinical testing programs, and to review clinical data and manufacturing facilities. I can further provide assurances that any vaccine authorized for widespread use will meet the appropriate standards for quality, safety and efficacy.

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