But while the impact for Europe may be cushioned, it could be a different story elsewhere. The Johnson & Johnson vaccine has been an important component of vaccination plans for countries around the world.

While it has not yet been rolled out at anything near the scale of AstraZeneca’s, some regions have pivoted to the shot amid AstraZeneca shortages. The African Union recently acquired 400 million doses.

The pause on Johnson & Johnson vaccinations in the United States, along with new restrictions on the use of AstraZeneca’s shot in Europe, rattled vaccination campaigns around the world relying on those vaccines. South Africa followed the United States in pausing Johnson & Johnson shots, though its health regulator in recent days recommended resuming its use.

U.S. health officials called for a pause in the vaccine’s use on April 13. Johnson & Johnson suspended its E.U. rollout immediately afterward, just as the first shipments of the shot were arriving in the region.

U.S. regulators and scientists are still studying the original reports of the clotting disorder and sifting through any new safety reports of possible cases of the clotting disorder. That effort has so far turned up little.

Dr. Rochelle P. Walensky, the C.D.C. director, said on Monday that health officials were investigating “a handful” of new, unconfirmed reports that emerged after the pause was recommended, to determine whether they might be cases of the rare blood clotting disorder.

“Right now, we are encouraged that it hasn’t been an overwhelming number of cases, but we are looking and seeing what has come in,” she said at a White House news conference.

Carl Zimmer contributed reporting from New Haven; Noah Weiland and Sharon LaFraniere from Washington; and Benjamin Mueller from London.

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