A sudden halt in Johnson & Johnson’s vaccine injected jitters into the nation’s COVID-19 inoculation campaign Tuesday, threatening to shake confidence in vaccinations six days before they’re opened to all adults.
Massachusetts quickly joined dozens of other states, including neighboring Rhode Island and New Hampshire, in adopting a federal recommendation to suspend the J&J shots as US health officials review a half-dozen cases of rare blood clots in women who had been given the single-dose vaccine. About 6.8 million Americans have received the vaccine so far.
“This is a rare but serious outcome that needs to be investigated,” said Dr. Howard Koh, professor at the Harvard T. H. Chan School of Public Health and a former public health commissioner in Massachusetts. Investigators will have to examine the blood clotting cases and determine if the J&J vaccine was “causal or coincidental,” he said.
It wasn’t clear how long the investigation would take and whether, or when, the J&J injections would be allowed to resume. Similar blood clotting linked to the AstraZeneca vaccine, not yet authorized in the United States, has prompted some European countries to restrict its use in certain age groups.
Some feared the J&J suspension could slow the broader US vaccination push at a critical juncture as fast-spreading coronavirus variants fuel fresh outbreaks.
The biggest risk may turn out to be “the potential damage that can be done to public trust,” Dr. Benjamin Linas, associate professor of epidemiology at Boston University’s School of Public Health, told state lawmakers Tuesday.
For residents who already received J&J shots, or scheduled them, the suspension was a jolt of bad news.
“It feels like a giant punch in the gut,” said high-tech employee Jonathan Kriner, whose wife got the J&J vaccine Monday. He was supposed to get his shot on Tuesday, but the appointment was canceled abruptly and no new one set.
“I feel like somebody’s got to know information I don’t,” he said. “It feels like a pretty extreme reaction for a blanket pullback.”
White House officials sought to assure the public that the pause in J&J shots won’t derail the Biden administration’s goal of administering 200 million vaccine doses in their first 100 days or having enough supply to immunize all Americans by the end of May. They said 28 million doses of the Pfizer-BioNTech and Moderna vaccines are being shipped to states this week.
“We have plenty of supply,” White House virus response coordinator Jeffrey Zients said Tuesday. “We have enough supply of Moderna and Pfizer to hit the targets that we’ve set.”
But many state officials, including Massachusetts Governor Charlie Baker, had hoped the J&J vaccine — which requires just a single shot and is easier to store — could play a key role in the coming weeks as vaccinators target hard-to-reach populations, such as rural and homebound residents, along with college students and others who are thought to be less likely to return for a second dose.
As recently as Monday, on a visit to a Worcester community health center, Baker said an increase in J&J doses would “create a ton of new capacity” for Massachusetts because vaccination sites wouldn’t have to book second shots.
“This vaccine, because it’s a one-dose vaccine, was a really good way to reach the disabled and other vulnerable populations,” said Dr. David Rosman, president of the Massachusetts Medical Society, who agreed pausing the J&J injections was the appropriate decision. “A lot of the plan to reach those populations had J&J in the center of it.”
Many colleges had also envisioned the one-and-done J&J formula enabling them to vaccinate students before they left campus at the end of the spring semester, said Gerri Taylor, the Sudbury-based cochair of the American College Health Association. “We wanted them to be immunized before they go home, and now that may not happen,” she said.
Because federal regulators cleared the J&J vaccine for emergency use two months later than the other vaccines, it has so far accounted for only about 5 percent of all US vaccine doses that have been administered so far.
Biden administration officials, however, had been counting on the J&J vaccine to help anchor the global effort to vaccinate other countries that lacked vaccine production capacity. Even before the J&J vaccine was authorized by the Food and Drug Administration, the United States had sent about 4 million doses it had already purchased to Canada and Mexico.
Independent trackers of the vaccination campaign said they worried the blood clotting scare could embolden vaccine opponents just as the general public becomes eligible for shots and government officials press a campaign to persuade hesitant pockets of the population to be immunized.
“We do have this very aggressive antivaccine movement using every opportunity to discredit vaccines,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.
Just hours after the Centers for Disease Control and Prevention and the FDA said they were investigating potentially dangerous clots that occurred 6 to 13 days after six women were given the J&J vaccine, the Massachusetts COVID-19 Response Command Center said it would pause giving the vaccine.
“This action is being taken out of an abundance of caution as the FDA and CDC review these six cases, none of which are known to be linked to Massachusetts,” a spokeswoman for the command center said. State residents who booked J&J vaccine appointments should reschedule with providers, she said.
All six cases being investigated occurred in women between ages 18 and 48, one of whom died. The clotting, called cerebral venous sinus thrombosis, was seen in veins that draw blood from the brain and was linked to low platelet counts.
“The fact that the public health system picked up on these clots so quickly shows the system is working,” said Dr. Philip Landrigan, director of Boston College’s global public health program and a veteran of the CDC. “It’s a setback, and it could slow things down a bit, but it’s too soon to know how serious it will be.”
Massachusetts lawmakers sought to assess the impact at a Tuesday hearing of a joint committee on COVID-19 and emergency preparedness. One of those who testified, Dr. Dan Barouch, head of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, whose research helped to develop the J&J vaccine, acknowledged the vaccine’s suspension could have a big potential impact.
“If one of the three vaccines either is not in use or has to be restricted . . . it will necessarily slow down the vaccine process,” he said. “But I think it’s currently an area of uncertainty.”
Barouch said that, in the general public, about one person in a million develops blood clotting in the brain each month, a rate similar to that of the people who received the J&J vaccine. Investigators, he said, must now determine whether the vaccine caused the clotting.
Hotez, at Baylor, said US regulators likely acted swiftly because of concerns among their European counterparts over a similar COVID-19 vaccine developed by AstraZeneca and the University of Oxford.
That vaccine also relies on an adenovirus to deliver part of the distinctive spike protein on the coronavirus into cells to trigger an immune response. Last week, amid that vaccine’s rollout in Europe, regulators there said they found a possible link between the shots and a very rare type of blood clot.
“The fact that both adenovirus vaccines seemed to be linked to that is enough of a concern even though it’s a rare event,” Hotez said. He said he hoped investigators decide by this weekend if the benefits of J&J’s vaccine outweigh its risks.
John R. Ellement and Emily Sweeney of the Globe staff, and Globe correspondent Charlie McKenna contributed to this story.