WASHINGTON — In yet another setback for Johnson & Johnson’s coronavirus vaccine, the Food and Drug Administration on Thursday limited its use to adults who cannot or refuse to get the Pfizer-BioNTech or Moderna vaccines, citing safety concerns.

The agency said 60 cases of a rare but serious blood-clotting disorder have been identified, including nine deaths, out of about 18 million doses administered. The action comes about five months after the Centers for Disease Control and Prevention recommended Moderna’s and Pfizer’s vaccines over Johnson & Johnson’s for booster shots.

The F.D.A. said that weighing the risks of Johnson & Johnson’s vaccine against the benefits, it had decided to limit its use to adults who cannot access Pfizer’s or Moderna’s vaccines, or for whom those shots are not “clinically appropriate.” One example would be people who experienced an extreme allergic reaction to the other two vaccines, the agency said.

It said the vaccine could also be given to adults who “would otherwise not receive a Covid-19 vaccine.”

Johnson & Johnson was eclipsed long ago by Pfizer and Moderna in the nation’s vaccination campaign; federal officials have said the mRNA vaccines produced by those companies are both safer and more effective. In a statement, Johnson & Johnson said the F.D.A.’s action reflected the already-known risk of the side effect, not new data on the rate at which it occurs. But in a sign of the firm’s own flagging interest in its vaccine, it has stopped providing sales outlooks for the shot to investors.

Reports that the vaccine can trigger a condition known as thrombosis with thrombocytopenia syndrome have bedeviled it from early on. In April 2021, not long after it was approved for emergency use, federal authorities paused distribution of the vaccine for a safety evaluation. Regulators lifted the pause 10 days later but added a warning to instructions for its use.

Then, in December, the C.D.C. recommended that adults seeking a booster shot choose Moderna or Pfizer instead of Johnson & Johnson, citing more benefits and lower risks. Coupled with a host of manufacturing troubles in the United States, some experts said,the agency’s judgment meant the federal government had all but written off Johnson & Johnson’s vaccine.

According to the F.D.A. announcement on Thursday, federal authorities now have 60 reports of the blood-clotting disorder — or four times as many as were reported when last year’s pause in distribution was lifted. In the interim, the number of Johnson & Johnson doses administered has slightly more than doubled, while the number of Pfizer and Moderna recipients has skyrocketed.

The number of deaths attributed to the disorder triggered by the Johnson & Johnson’s vaccine does not appear to have risen much, if at all. But there have been far fewer, if any, suspected deaths due to side effects from the mRNA vaccines, federal health officials have said.

In its announcement, the F.D.A. cited more than six cases and close to one death attributed to the blood clotting disorder for every two million shots of Johnson & Johnson vaccine administered in the United States.

About 17 million Americans have now gotten one dose of Johnson & Johnson’s vaccine, and another 1.5 million have gotten a booster dose, according to the C.D.C.’s data. By comparison, about 200 million Americans have gotten at least two doses of either Moderna’s or Pfizer’s vaccine.

Trying to cast the tight new restrictions in a positive light, Johnson & Johnson said: “Data continue to support a favorable benefit-risk profile for the Johnson & Johnson COVID-19 vaccine in adults, when compared with no vaccine.”