Clear messaging is one of the most powerful tools that public health officials have, but only when they use it. And the C.D.C. and the Biden administration did not do so yesterday. They failed to convey whether they wanted the entire country to begin changing its behavior — or whether they were focusing on only some regions, which happen to be the very places that require special attention to reach.

The new guidelines will still probably help somewhat. The highly contagious Delta variant has fueled a rise in cases across the country, which means that masks may make at least a small difference almost everywhere. But more frequent masking in heavily vaccinated communities will almost certainly not make a major difference. The much larger problem is that more than 30 percent of eligible Americans have not been vaccinated…

Some experts also said that Americans, frustrated by the long pandemic, need to hear a clear plan for what will allow the masks to come off. “If we want to continue to ask people to step up,” Jennifer Nuzzo, a Johns Hopkins University epidemiologist, told The Times, “we need to give them a vision of what we’re working toward.”