| When Pfizer and BioNTech released positive vaccine results Monday, the floodgates of optimism opened. The companies' announcement of more than 90% effectiveness in a study of some 44,000 people suggested that a way out of the pandemic may be at hand. Airwaves were flooded with scientists and other observers explaining the findings, and equity indexes gained as long-battered travel and entertainment stocks soared. Yet many questions about the vaccine—who it protects, for how long, and from what—still remain to be answered. The study was designed primarily to show that the shot wards off symptomatic cases of Covid-19, not infections. It still needs to show whether those who get the vaccine are less likely to suffer severe, potentially deadly forms of the disease. Its performance in key groups such as the elderly and people with chronic health conditions like diabetes is to be determined. And the four-month-old study can't tell us how long protection lasts.  Photographer: NurPhoto/NurPhoto Photographer: NurPhoto/NurPhoto Even when all these boxes are ticked, the vaccine must be manufactured, distributed and administered. The companies expect to make some 50 million doses this year and about 1.3 billion in 2021. But divide those numbers in half, because each person needs two shots to be immunized. Then there's the challenge of storing the vaccine at ultra-low temperatures, requiring equipment many communities lack, even in the U.S. It's also important to continue watching those who received the vaccine for years. The messenger RNA technology used in the Pfizer/BioNTech vaccine has never been deployed in humans before. That adds up to many more questions and a lot more work from governments, scientists and health workers. "A positive signal would be exciting," said Richard Hatchett, chief executive officer of the Coalition for Epidemic Preparedness Innovations, "but it certainly wouldn't mean that the pandemic is about to be over."—John Lauerman | 
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