Anecdotes tell us what the data can’t: Vaccinated people appear to be getting the coronavirus at a surprisingly high rate. But exactly how often isn’t clear, nor is it certain how likely they are to spread the virus to others. And now, there’s growing concern that vaccinated people may be more vulnerable to serious illness than previously thought. There’s a dearth of scientific studies with concrete answers, leaving public policy makers and corporate executives to formulate plans based on fragmented information. While some are renewing mask mandates or delaying office reopenings, others cite the lack of clarity to justify staying...