Roughly 17 million Americans received the Johnson & Johnson Covid vaccine, only to be told later that it was the least protective of the options available in the United States. But new data suggest that the vaccine is now preventing infections, hospitalizations and deaths at least as well as the Pfizer-BioNTech and Moderna vaccines.

The reasons aren’t clear, and not all experts are convinced that the vaccine has vindicated itself. But the accumulating data nonetheless offer considerable reassurance to recipients of the vaccine and, if confirmed, have broad implications for its deployment in parts of the world.