“Usually, an anticoagulant drug called heparin is used to treat blood clots. In this setting, administration of heparin may be dangerous, and alternative treatments need to be given,” the statement said.
Like many states, New York had already prepared for a significant drop in its supply of the Johnson & Johnson vaccine after federal officials said that supplies would be limited because of a production issue at a Baltimore manufacturing plant. On Friday, Gov. Andrew M. Cuomo said that New York expected to receive 34,900 Johnson & Johnson shots, a decrease of 88 percent from the previous week.
Dr. Zucker, New York’s health commissioner, said that the state would honor appointments made at state-run mass vaccination sites for the Johnson & Johnson vaccine by giving people the Pfizer-BioNTech vaccine instead. That vaccine requires two doses, and it was not immediately clear how the state would handle the additional strain on its supply.
New Jersey health officials said the state would work with its vaccination sites to help people get appointments for the Pfizer or Moderna vaccine instead. Mayor Bill de Blasio of New York City said that the city would do the same, rescheduling appointments at city-run vaccine sites.
“Every site has been told this morning to stop giving the J&J shots,” he said at a news conference.
The city’s health commissioner, Dr. Dave Chokshi, said that around 234,000 residents have received the Johnson & Johnson vaccine and none had reported any blood clots so far. The city had been relying on the vaccine to inoculate hard-to-reach New Yorkers, including people who are homebound.
Both Mr. Cuomo and Mr. de Blasio received the Johnson & Johnson vaccine at separate appearances last month, which they framed as an effort to boost confidence in that vaccine’s efficacy rate and to address vaccine hesitancy.
Regulators in Europe and elsewhere are concerned about a similar issue with another coronavirus vaccine, developed by AstraZeneca and Oxford University researchers. That vaccine has not been authorized for emergency use in the United States.
Rebecca Robbins contributed reporting.