The Food and Drug Administration is about to make the most momentous decision in its history: whether to authorize the early use of a vaccine to protect against the coronavirus without the normal safety and effectiveness protocols.

This is happening against the backdrop of the presidential election season, in which the pandemic has become a fraught political issue for the Trump administration. The wrong decision could seriously undermine efforts to prevent the spread of this deadly virus.

Significant risk may be acceptable for drugs intended to treat patients with serious, life-threatening diseases. The F.D.A. will approve a cancer drug with significant side effects, for instance, if it is demonstrated that the drug may prolong the life of the patient.

But for a vaccine, the agency has always demanded a higher level of assurance of safety, for a simple reason: The vaccine will be given to healthy people.

In 2004, Congress authorized the F.D.A. to issue emergency authorizations for medical products with less evidence of safety and efficacy than is ordinarily required. The theory was that, in a national emergency, it may be necessary to relax stringent standards to fast-track a potentially risky but lifesaving medical product.

Under this lower standard, if the F.D.A. finds that a product “may be effective” and that its potential benefits outweigh its risks, the agency can authorize its emergency use. But this discretion also means that the agency should not authorize a vaccine if its use could undermine public health — in other words, when it could do more harm than good.

This decision, which should be left to the F.D.A.’s scientists after consultation with public health experts outside the agency, will be enormously complicated. My own view, informed by my years at the agency as its head of policy, is that a coronavirus vaccine for the general public should be required to meet the traditional safety and efficacy standards, not ones potentially compromised by haste. But an emergency-use authorization might appropriately be used to dispense with some of the less important data analyses.

As the F.D.A. contemplates an accelerated approval process, it should be guided by three considerations.

First, will use of a partially effective vaccine lead to risky behavior that outweighs the vaccine’s benefits? The F.D.A. has approved flu vaccines that have an effectiveness rate below 40 percent and has said that a coronavirus vaccine must be at least 50 percent effective. If the vaccine doesn’t fully protect those who take it, will it give users a false sense of security and lead to more risky behavior — less social distancing and use of masks, more frequenting of restaurants, movie theaters and other indoor activities?

Second, will an early authorization undermine public acceptance of later, safer, more effective vaccines? A vaccine authorized with only limited data might cause harm that can be detected only after more extensive use. The agency will have only one chance to get this right. If significant numbers of people get seriously ill or die from the first vaccine, the public will lose trust in the F.D.A. and reject subsequent vaccines even if they are proved to be much stronger and safer.

Third, the F.D.A. must consider the impact of an emergency authorization on existing vaccine studies. There are almost 40 continuing vaccine clinical trials, and several have been identified as promising. Those trials are blind, which means that the participants do not know whether they are getting the vaccine or a placebo. Would some participants drop out and opt for the newly authorized vaccine, undermining those studies? Would the trials be able to recruit additional participants who would risk getting a placebo once there was an authorized vaccine?

Only if the agency takes this broad view will it reach the decision that in the long run will protect the most people from this dreadful pandemic.