Last week, Stephanie Gaydos cried tears of joy when Delaware County confirmed she finally had an appointment to receive a dose of Johnson & Johnson’s COVID-19 vaccine.

Tuesday morning, as the Havertown woman dropped her son off at school, she learned federal authorities had paused the vaccine’s distribution due to reports of blood clots in six women. This time, the tears came out of frustration.

“It felt like I was so close to normalcy,” Gaydos, 35, said, “and it just got snatched away.”

Across the region, the Centers for Disease Control and Prevention and Food and Drug Administration’s recommendation to press pause on the J&J vaccine pending a federal review prompted governments, pharmacies, and health-care providers to put J&J vaccinations on hold, upending plans, even as they stressed the pause is temporary and the risks are low.

The news came on the very day Pennsylvania opened appointments to all adults, and officials worked to bolster confidence in the overall safety of vaccination.

“Taking a pause to evaluate a potential side effect is exactly how a data-driven, scientific process should work, and I hope Pennsylvanians will be reassured by this step,” said Val Arkoosh, Montgomery County Commissioners’ chair and a physician. “We have to balance speed and safety as we try to get more shots in arms, and this pause gives me confidence science and safety are guiding that process.”

Philadelphia, which had counted on more than 80,000 doses of J&J from the Federal Emergency Management Agency for the Convention Center clinic over the next two weeks, will now have to dig into its own supply of Pfizer-BioNTech vaccine to keep the clinic running.

“If not for the health department’s stockpile,” said James Garrow, an agency spokesperson, the site “would shut down tomorrow.”

» READ MORE: Scientists race to unravel the mystery of very rare clotting connected with Johnson & Johnson vaccine

Five days after opening, the Esperanza Community Vaccination Center in North Philadelphia already was correcting under-vaccination of the city’s communities of color. About 58% of the doses distributed there have gone to Hispanic recipients. The clinic had planned to offer only J&J doses this week, though, and people with appointments Tuesday were told they would have to come back. The site will reopen Wednesday and offer the Pfizer-BioNTech vaccine, which, unlike the single-dose J&J, requires two shots, given several weeks apart.

Lucy Puentes, 36, had been visiting relatives in Philadelphia for three weeks after her mother got sick from COVID-19, and wanted to be vaccinated at the Esperanza site Tuesday. She won’t be allowed home into the Dominican Republic without either a vaccination card or a negative COVID-19 test 72 hours prior to her trip.

“I was hoping to get this vaccine because it’s just one dose,” she said. “But, now, I just want to go back to my kids.”

Meanwhile, case counts continue to rise, said Thomas Farley, Philadelphia’s health commissioner, who noted Tuesday that hospitalizations and deaths also are increasing.

“If you think this epidemic is over, you are mistaken,” Farley said at a news conference. “This COVID-19 epidemic is still here, and it is still deadly.”

The loss of J&J doses, and the city’s reallocation of the shots they have, will force some neighborhood clinics to be canceled, Farley said.

CVS, RiteAid, and Walgreens all said they had stopped providing the J&J vaccine, and were contacting people whose appointments had been canceled to reschedule. Penn Medicine has postponed several clinics and paused use of the J&J vaccine systemwide. Penn had been using the single-dose vaccine as part of its senior housing and homebound vaccination program; no patients had reported serious side effects. At Albert Einstein Medical Center, plans to use about 70 doses of J&J vaccine on homebound patients had been paused. Jefferson Health has not paused its clinics but is not using J&J doses.

The suburban counties surrounding Philadelphia were rescheduling appointments or shifting to one of the two-dose vaccines at their clinics. Bucks County officials noted they rely on Pfizer-BioNTech doses at all but one of their county-run clinics. Pennsylvania health officials announced a halt to J&J vaccinations until “at least” April 20, and New Jersey was halting them “until further notice,” Health Commissioner Judith Persichilli said in a statement.

» READ MORE: North Philly mass vaccination site opens as city prepares for steep drop in J&J doses

The six women identified with blood clots developed them within 13 days of getting the J&J vaccine; one of the women has died. Experts stressed that more than six million Americans have received this vaccine, making the complication -- if indeed it turns out to be definitively linked to the product -- far more rare than the risk of dying of COVID after contracting the illness.

Pennsylvania’s largest teachers’ union said Tuesday that most of the 112,000 school staff statewide who received the J&J vaccine got the doses more than two weeks ago.

Tuesday’s pause is the second setback for the vaccine; earlier this month, 15 million doses had to be discarded due to a manufacturing error at a plant in Baltimore. That error, however, meant that far fewer doses were being delivered. J&J doses represented less than a quarter of Philadelphia’s vaccine allocation last week, and about 3% of the city’s total vaccine supply this week.

Vaccines and health equity

Ruth Faden, the founder of the Johns Hopkins Berman Institute of Bioethics, said it’s too early to know how the pause will affect the nation’s vaccine rollout. About 18% of all fully vaccinated Pennsylvanians and 23% of fully vaccinated New Jersey residents received J&J doses, according to the CDC.

“I don’t want to communicate that this is a terrible, significant setback,” she said. “The U.S. is in a much better position than other countries in terms of its vaccine supply pipeline.”

But the fact that it is a single dose and doesn’t require the arduous storage and transfer processes of the Pfizer and Moderna vaccines has meant that the J&J vaccine is especially helpful to reach people who have less access to health care.

That could be anyone from people who live in rural areas without cold storage capacity, people who are homeless and hard to consistently reach, or people who simply cannot get to two separate vaccine appointments.

“That’s your worry. What’s going to happen to the groups for whom this was tailor-made?” Faden said. “The equity objectives and the equity priorities don’t change. We have to keep our foot on the throttle, we have to be as committed to those same equity objectives as we were before, even if they become somewhat more difficult to fulfill.”

Philadelphia’s Black Doctors COVID-19 Consortium has used the J&J vaccine for 4,000 inoculations but said it would use other vaccines while the J&J risks are investigated.

“What I know, I will share. If it doesn’t seem safe, I’ll tell you, ‘It’s not safe,’” Ala Stanford, the group’s founder, said. “If people have questions, we want to be a source for them to get their questions answered, especially if they don’t have a doctor to go to.”

The majority of the doses allocated to Philadelphia and the states are either Pfizer or Moderna, and Farley said the city will continue efforts to reach people living in transient conditions.

“It will make it more complicated to reach those people for the two doses,” he said. “We will have to adjust.”

Fears on two fronts

Doctors and pharmacists in the area are facing pressure from patients on two fronts, they said. Some are afraid after getting the Johnson & Johnson vaccine, said Christine Meyer, a physician from Exton. Others are panicking that they won’t be able to be vaccinated.

“The people afraid about not being able to get a vaccine now, we’re in a different era now than we were a few weeks ago,” she said. “For people who have already gotten it, you obviously can’t take it back, and it’s really important, over and over again, to educate people how rare this is.”

The pause had already begun rattling people waiting to be vaccinated. Felicita Guerra, from Philadelphia’s Hunting Park neighborhood, went to the Esperanza site to make an appointment but now doesn’t want the J&J shot.

“My neighbors told me that they are having some bad side effects,” she said. “So, I’m not getting that one. You crazy!?” (The vast majority of side effects with COVID-19 vaccines, ranging from soreness at the injection site to flulike fever and headache, are uncomfortable but temporary.)

Epidemiologist Chrysan Cronin, who heads the public health department at Muhlenberg College, said people may be alarmed by headlines implying the vaccine could cause blood clots, but said an analysis of the facts showed a low risk.

“Less than one in a million people have had this rare reaction,” she said. “The risk of this potential reaction … is far less than the risk of blood clots due to COVID, for example, or the risk of blood clots due to the birth control pill.”

She noted that the FDA implemented the pause in order to have time to alert health-care providers about how to treat the very rare clots and that the vaccine has not been determined to be the cause of the blood clots. She also said the pause is a reminder that the FDA is “right on top of these things” and ensuring safety of the vaccines available in the United States, something that should instill public confidence.

“This is just one more way that the misinformation can be twisted; we’re going to have to deal with that,” Cronin said, but, she added, “I really in the long run don’t think it’ll do too much damage.”

Staff writers Allison Steele, Erin McCarthy, Oona Goodin-Smith, Maddie Hanna, and Chris A. Williams contributed to this article.