Early in the pandemic, many health experts — in the U.S. and around the world — decided that the public could not be trusted to hear the truth about masks. Instead, the experts spread a misleading message, discouraging the use of masks.

Their motivation was mostly good. It sprung from a concern that people would rush to buy high-grade medical masks, leaving too few for doctors and nurses. The experts were also unsure how much ordinary masks would help.

But the message was still a mistake.

It confused people. (If masks weren’t effective, why did doctors and nurses need them?) It delayed the widespread use of masks (even though there was good reason to believe they could help). And it damaged the credibility of public health experts.

“When people feel as though they may not be getting the full truth from the authorities, snake-oil sellers and price gougers have an easier time,” the sociologist Zeynep Tufekci wrote early last year.

Now a version of the mask story is repeating itself — this time involving the vaccines. Once again, the experts don’t seem to trust the public to hear the full truth.