By Liz Essley Whyte & Peter Loftus

The Food and Drug Administration limited the use of the Covid-19 vaccine from Johnson & Johnson after reviewing the risk of life-threatening blood clots.

The agency said Thursday that the J&J shot’s authorization was now only for adults for whom other shots aren’t available or medically appropriate, or who won’t take another vaccine.

The FDA said it was making the move after confirming a total of 60 cases, including nine deaths, of the clotting condition known as thrombosis with thrombocytopenia syndrome, or TTS, among the millions of people who got the J&J shot.

The change will likely sharply scale back use of a vaccine that health authorities had once hoped would be a convenient option for many people, but has become a third choice for most people because of the emergence of the risk for the rare but life-threatening side effect.

In the U.S., roughly 17 million people have gotten the J&J vaccine, compared with more than 202 million who received two doses of the authorized Covid-19 vaccines from Pfizer Inc. and partner BioNTech SE and from Moderna Inc., according to the Centers for Disease Control and Prevention.

Because of the risk for the clotting condition, the CDC in December recommended that patients opt for one of the other vaccines over the Johnson & Johnson shot.

“Our action reflects our updated analysis of the risk of TTS following administration of this vaccine and limits the use of the vaccine to certain individuals,” said Peter Marks, who leads the FDA division responsible for regulating vaccines.

J&J said it has updated the fact sheet for its vaccine to increase awareness of the clotting condition. “Data continue to support a favorable benefit-risk profile for the Johnson & Johnson COVID-19 vaccine in adults, when compared with no vaccine,” the company said.

U.S. health authorities in April 2021 paused the use of J&J’s vaccine to investigate the clotting-condition risk.

Later that month, the authorities allowed the one-dose shot’s use to resume, saying the benefits outweighed the risks.

Yet the pause prompted many people to choose the Pfizer-BioNTech and Moderna shots, and the FDA and CDC monitored reports of the blood-clotting condition among people who developed cases after vaccination.

The FDA said it decided to limit use of the vaccine not just because of the number of clotting incidents confirmed so far, but also because scientists don’t currently know what risk factors lead to vaccinated patients developing the syndrome. The agency also said the illness can cause patients to deteriorate rapidly, even if a doctor diagnoses the condition quickly.

The 60 cases and nine deaths of the clotting condition confirmed by the FDA took place through March 18, the FDA said. The agency said it had determined 3.23 cases of TTS were reported for every million doses of the J&J vaccine administered, and that 0.48 deaths were reported per million doses of the vaccine administered.

The agency said J&J’s vaccine was also still authorized for adults who have had an allergic reaction to one of the messenger RNA vaccines from Pfizer-BioNTech and Moderna or who would otherwise not receive a vaccine, including those who have “personal concerns” with the mRNA vaccines.

The vaccines from Pfizer and Moderna use RNA-based technology, while J&J’s vaccine has a different design. It uses a common virus, an adenovirus, to deliver a gene that sets off an immune response against the coronavirus.

A Covid-19 vaccine from AstraZeneca PLC uses a similar design and has been linked to an increased risk of TTS. That vaccine is available in other countries, but not in the U.S.

Initially, health authorities and experts said J&J’s vaccine would be an important tool for vaccinating residents of poor countries with large rural populations, as its one-dose regimen often makes it easier to administer in far-flung locations.

The vaccine also can be stored at higher temperatures than the Pfizer-BioNTech and Moderna vaccines.

Yet the safety concerns combined with manufacturing problems that limited supply have diminished the role of J&J’s vaccine. Sales of the vaccine—which has a relatively low, not-for-profit price—were $2.4 billion for 2021. J&J recently withdrew its previous forecast of $3 billion in sales for 2022, citing a global surplus of doses and uncertain demand.