Top health officials urge Americans to get vaccinated but barely address the J.&J. dose pause.

Three top federal health officials appeared on Capitol Hill on Thursday and implored Americans to get vaccinated against the coronavirus, but said little about the investigation into whether the Johnson & Johnson vaccine may be linked to a small number of cases of rare blood clots, or when that vaccine might be put back into use.

“Hopefully we’ll get a decision quite soon, as to whether or not we can get back on track with this very effective vaccine,” Dr. Anthony S. Fauci, President Biden’s top medical adviser for the coronavirus, told a House panel.

Dr. Fauci’s comments came as the future of the Johnson & Johnson one-shot vaccine hung in the balance. Earlier this week, the Food and Drug Administration and the Centers for Disease Control and Prevention called for a pause in the use of the vaccine in the wake of reports of a small number of rare blood clots in recipients. Though it is unclear whether the vaccine was responsible for the clots, injections came to a sudden halt across the country.

On Wednesday, a C.D.C. advisory panel suggested that it would be a week to 10 days before they had enough information to assess the vaccine’s risks and could make a decision about its future. In the meantime, the officials — Dr. Fauci; Dr. Rochelle Walensky, the C.D.C. director; and Dr. David Kessler, who runs the Biden administration’s vaccine effort — urged Americans to continue to get vaccinated.

an immediate pause in the use of Johnson & Johnson’s single-dose Covid-19 vaccine after six recipients in the United States developed a rare disorder involving blood clots within one to three weeks of vaccination.

All 50 states, Washington, D.C. and Puerto Rico temporarily halted or recommended providers pause the use of the vaccine. The U.S. military, federally run vaccination sites and a host of private companies, including CVS, Walgreens, Rite Aid, Walmart and Publix, also paused the injections.

Fewer than one in a million Johnson & Johnson vaccinations are now under investigation. If there is indeed a risk of blood clots from the vaccine — which has yet to be determined — that risk is extremely low. The risk of getting Covid-19 in the United States is far higher.

The pause could complicate the nation’s vaccination efforts at a time when many states are confronting a surge in new cases and seeking to address vaccine hesitancy.

Johnson & Johnson has also decided to delay the rollout of its vaccine in Europe amid concerns over rare blood clots, dealing another blow to Europe’s inoculation push. South Africa, devastated by a more contagious virus variant that emerged there, suspended use of the vaccine as well. Australia announced it would not purchase any doses.