PREPARE FOR many more ups and downs, but the announcement from Pfizer and its partner BioNTech of Germany is a genuinely promising moment in the difficult battle against the coronavirus pandemic. No one has ever won regulatory approval for an effective vaccine that uses messenger RNA (mRNA) to stimulate an immune response. Now, the pharma companies say their experimental vaccine is more than 90 percent effective at preventing covid-19.

The companies have a large Phase 3 clinical trial underway with 43,538 volunteers, and the announcement was based only on preliminary results. But should it hold up, the significance is that one of the most promising and new technologies does work at preventing infection. That may well mean that other vaccines will also work, that we can banish from our thoughts the worst-case scenario of “no vaccine,” and that the world will find a way out of a disease that has already taken 1.2 million lives.

The mRNA vaccines offer the potential for rapid, inexpensive and scalable manufacturing. Pfizer said it expects to produce 50 million doses this year and 1.3 billion next year. One downside is that the two-dose vaccine must be stored at ultracold temperatures, which could create serious logistical headaches in distribution. The data shows it brought protection 28 days after the first shot. In the next step, the companies must steer the vaccine to an Emergency Use Authorization from the Food and Drug Administration, which they are expected to seek at the end of this month. The most vulnerable along with front-line health-care workers must go first. For most, a vaccine is still most likely in 2021, at the earliest.

Pfizer and BioNTech managed this feat on their own, without development money from Operation Warp Speed by the U.S. government. This is further confirmation that the enormous concentration of brainpower and resources brought to bear against covid-19 may eventually pay off. No single vaccine will be the answer; rather, several successful ones will be needed to battle the disease.

President-elect Joe Biden rolled out an experienced advisory committee on Monday and pledged to create “detailed plans built on a bedrock of science,” a welcome change of tune from President Trump’s reckless disregard for biomedical advice. Mr. Biden also demonstrated he’s attuned to the need to win back public trust, speaking forthrightly about what’s ahead. “The challenge before us right now is still immense and growing,” he said. “We’re still facing a very dark winter.”

That is an understatement. Mr. Biden has properly addressed the persistent shortages in diagnostic testing, personal protective equipment and other issues, and on Monday he implored Americans to wear a mask, one of the most vital mitigations. But these are not going to be enough. The nation faces a massive, surging wave of infection into a population dangerously fatigued and complacent. Until the vaccine arrives, the pandemic demands a far more vigorous response. We hope Mr. Biden continues to work on it as he waits to take the reins.

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