Efficacy is merely one layer, though. The Pfizer and Moderna vaccines have an edge at preventing symptomatic illness, but the Johnson & Johnson vaccine brings its own advantages. It has no demanding freezer requirements, which means it’s easier to distribute and more accessible to many communities. It’s more affordable than the other two—the company is providing it at cost around the world. Then there’s the fact that resources can be stretched a lot further when only a single dose has to be administered.

For individuals, too, the Johnson & Johnson vaccine has benefits. As a one-and-done injection, it’s more convenient. It also has a lower rate of adverse events than Moderna’s. You can’t compare results of these trials too precisely, but there are indications of a striking difference. About 2 percent of those who got the Johnson & Johnson vaccine recorded having reactions, such as fatigue, muscle aches, and fever, that were severe enough to interfere with daily activities. For those getting their second injection of Moderna, that rate was higher than 15 percent. People who are on the fence about getting vaccinated may find that this difference tips the scales in favor of getting a shot. Others who have doubts about the newness of the mRNA technology in the Pfizer and Moderna vaccines may appreciate the fact that Johnson & Johnson’s approach has already been deployed in the company’s Ebola vaccine, which got full drug approval in Europe last year.

Given these concerns, there’s some danger in the message—however well intentioned—that the COVID-19 vaccines are all the same by any measure, or that they’re perfect wards against severe disease.