“We are concerned about heightened reservations about the J&J vaccine, but in addition to that, those reservations could spill over into public concerns about other vaccines,” said Dr. Paul Simon, the chief science officer for the Los Angeles County Department of Public Health... “It’s a messaging nightmare,” said Rachael Piltch-Loeb, an expert in health risk communications at the N.Y.U. School of Global Public Health. But officials had no other ethical option, she added. “To ignore it would be to seed the growing sentiment that public health officials are lying to the public.”... “This is exactly the wrong situation at the wrong time at the very moment that Republicans are reconsidering their hesitancy,” said Frank Luntz, an American pollster who studies messaging for Republicans, a group that has exhibited high levels of skepticism about the coronavirus vaccines. Brian Castrucci, an epidemiologist and head of the de Beaumont Foundation, which studies public health attitudes, said: “It’s an easy turn to, ‘If they kept this from us, what else have they kept from us?’ We need to get out in front of this very quickly. ”