American pharmaceutical giant Johnson & Johnson on Tuesday announced that it will delay the rollout of its coronavirus vaccine in Europe as health authorities in the United States investigate reports of blood clotting in some recipients.

The announcement came shortly after the United States Centers for Disease Control and the Food and Drug Administration recommended pausing the use of the vaccine. The agencies said they were reviewing data involving six reported cases of a “rare and severe type of blood clot” in the recipients of the vaccine. More than 68 lakh doses of the vaccine have been administered in the US.

Johnson & Johnson said that it was reviewing these cases with European health authorities. “We have been working closely with medical experts and health authorities, and we strongly support the open communication of this information to healthcare professionals and the public,” the company added.

Meanwhile, the European commission asked the company to urgently clarify its “completely unexpected” decision to delay the rollout, The Guardian reported.

Johnson & Johnson’s single-dose vaccine had proven to be 72% effective at preventing all Covid-19 cases and 86% effective at preventing severe ones in larger clinical trials.

The vaccine was also approved for use in Thailand and South Africa. The company is also in talks with the Indian government to start early-stage clinical trials of its jab.

Health experts are also investigating a possible link between blood clotting and AstraZeneca’s coronavirus vaccine.