A mass vaccination site in North Philadelphia opened Friday, promising to bring thousands of doses to a community that is one of the most undervaccinated in the city.

The Esperanza Community Vaccination Center’s debut, though, comes as the city — along with the rest of the nation — faces next week a drastic drop in its supply of Johnson & Johnson COVID-19 vaccine, just before eligibility opens to all adults April 19. The vaccine maker has had to slash production due to problems with its contract manufacturer in Baltimore that must win federal approval after a major contamination incident.

Philadelphia is slated to receive 2,800 doses of the one-shot Johnson & Johnson vaccine next week, according to data from the Centers for Disease Control and Prevention. That’s a fraction of the 23,500 doses that were delivered this week.

“Particularly for the next few weeks,” said Thomas Farley, the city’s health commissioner, “we’re going to have to be careful about how we allocate vaccine.”

Adding to the pressure: the Federal Emergency Management Agency, which has bolstered the city’s supply with an additional 42,000 shots a week administered at the Pennsylvania Convention Center, is turning off that spigot April 26.

After that planned end of the program, “We will not be providing vaccine for the site,” said Janice Barlow, acting FEMA Region 3 Administrator, at Friday’s opening of the new smaller clinic, which FEMA is administrating, but isn’t providing with additional doses.

Area members of Congress are lobbying the White House to intervene, arguing that withdrawing the Convention Center doses would undermine the city’s ability to ensure vaccination in underserved communities. Farley said the city does not have the vaccine supply to keep operating what has been the city’s largest single supplier of vaccine.

FEMA does not control vaccine allocation, a spokesperson said, and planning for sites such as the Convention Center clinic is done with the expectation that they will be operating over an eight-week window.

Johnson & Johnson is the only single-dose vaccine available in the U.S. That convenience appealed to Trena Brown, who got a shot at the new clinic Friday.

“I don’t like needles,” she said.

The 49-year-old has asthma and high blood pressure, she said, conditions that could make a COVID-19 infection especially risky. She calmed her nerves about the shot by looking in the other direction, but later said she barely felt it.

“It’s pretty good,” she said as she left the clinic. “It’s really fast.”

» READ MORE: As expanded eligibility looms, Philadelphia races to vaccinate more than half its senior population

Throughout the vaccine rollout, poorer communities of color have received vaccine at a much lower rate than the city’s wealthy and whiter zip codes. Advocates and public health experts say that disparity shows the need to reach out to people who can’t access digital scheduling systems and can’t travel long distances to get a vaccine.

The new clinic, hosted by the community advocacy group Esperanza, “is one example of how we are working aggressively to reduce and eliminate inequality,” said Mayor Jim Kenney at a news conference at the site Friday.

Friday’s soft launch offered about 1,000 doses to essential workers, officials said, but in time the site is expected to provide up to 3,000 doses a day. It will operate Saturday through Thursday, with evening hours Wednesday and Thursday to accommodate people seeking shots after work. The site will allow people to make appointments, but will also vaccinate walk-ups.

» READ MORE: Philly is trying to bridge vaccine gaps by targeting hard-hit neighborhoods. Finally, activists and experts say.

In advance of the clinic’s opening, Esperanza staff have canvassed the neighborhood to boost awareness of the site, engaging with seniors in both English and Spanish. Many of the people receiving shots Friday morning said Spanish was their primary language. Just 16% of the city’s Hispanic population has had at least one dose, compared to 33% of white residents, according to city data. About 18% of Black Philadelphians have received at least one dose.

“Ensuring this site was made possible within walking distance for residents where all of the barriers were eliminated, especially the language barrier, is a huge win for our community,” said Quetcy Lozada, Esperanza’s vice president of community engagement and organizing.

Though FEMA is involved with administering the North Philadelphia site, all doses there come out of the city’s allocation.

Philadelphia is not alone in facing a significant drop in vaccine doses next week. Pennsylvania is receiving about 149,000 fewer Johnson & Johnson doses next week than it got this week. New Jersey will receive 15,600 Johnson & Johnson doses next week, 116,000 fewer than it got this week. The supply could decline to as few as 5,200 the week after that, said Judith Persichilli, the state’s health commissioner.

“The variability in doses is a reality,” she said, “and it’s very difficult to deal with.”

There will be about a third fewer first doses of all vaccines allocated to Philadelphia, Pennsylvania, and New Jersey next week, similar to the rate of reduced supply nationwide. Pennsylvania noted it had about 36,000 unused doses that could be administered next week.

About 15 million doses of J&J vaccine had to be discarded after failing to meet quality standards at a manufacturing plant in Baltimore. Farley could not confirm whether that was the cause of Philadelphia’s drop in supply.

The Biden administration, though, blamed the national supply decline on the manufacturing issue, saying Friday that the problem will linger until the Baltimore plant gets FDA authorization to resume production.

Farley said the Esperanza site was supposed to provide only J&J shots for the first two weeks of its eight-week run, but will shift to the two-dose Pfizer product after a week of administering J&J shots.

Staff Writers Jonathan Lai, Justine McDaniel, and Allison Steele contributed to this story.