The Latest Vaccine News Doesn’t Tell the Full Story

The drugmakers Moderna and Pfizer buoyed hopes for an end to the coronavirus pandemic when they announced this month that their vaccines were 94.5 percent (Moderna) and 90 percent (Pfizer) effective at preventing Covid-19, based on preliminary results from ongoing clinical trials. Neither vaccine produced any serious safety concerns.

Pfizer’s and Moderna’s data were analyzed by independent experts, though their findings were published in news releases, not peer-reviewed scientific journals, so the results are not yet considered conclusive. But if the numbers hold steady through the end of the trials,...