All Philadelphia adults will be eligible for vaccination against COVID-19 in less than two weeks, a policy shift announced Tuesday that aligns the city with President Joe Biden’s accelerated vaccination timeline.

Philadelphia plans to make shots available to everyone in the city over age 16 by April 19. Both New Jersey and Pennsylvania, which is conducting a vaccine rollout independent of Philadelphia’s, have said they have the same deadline.

The city’s new target for full eligibility, about two weeks earlier than the May 1 date the city committed to just last week, brings added complications to the vaccination process. Health officials are concerned groups now eligible for vaccination, particularly seniors, could be crowded out as scores of computer-savvy young people are better able to navigate the appointment system and seek shots.

“I do worry that young people will get in and it may be harder for people over the age of 65 to get in,” said Thomas Farley, the city’s health commissioner. “We’re asking younger people maybe you should wait a little bit.”

By contrast, Gov. Tom Wolf said he’s not concerned about demand outstripping supply as eligibility expands. “We are in a very different place,” in terms of the federal vaccine supply than when the rollout began, Wolf said Tuesday. And “both the 1B and 1C categories are a lot smaller than the 1A category was.”

But like the state, where the testing positivity rate is now over 9% and a more contagious British variant of the virus is growing more common, the city is in the midst of another surge in cases, Farley said. It is averaging 507 cases per day, double the count a month ago, and the COVID-19 test positivity rate is now 8.7%, well over the 5% experts say may point to wider community spread. Those infected increasingly skew younger, he said, but only 45% of residents age 65 and older are at least partially inoculated. Those older residents should get vaccinated immediately to reduce the risk of serious illness and death, Farley said. He has asked vaccine providers to make it easier for seniors to get shots by offering walk-up access.

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Farley wasn’t specific about how long younger people, who are at far less risk of serious illness or death if infected by the coronavirus, should wait before seeking appointments. It depended, he said, on how great demand is as eligibility expands.

On Monday, everyone in the 1C category will be eligible for vaccination in the city, if they can’t work remotely, Farley said. Those eligible include workers in transportation, construction, landscaping, information technology and telecommunications, public health, government and elections, social service, higher education, finance, media, and legal professions.

The city is entering this most expansive stage of the vaccine rollout as the Convention Center clinic run by the Federal Emergency Management Agency is nearing the end of its mandate. The clinic, which is currently providing second doses, will shift to offering the single-dose Johnson & Johnson vaccine starting next week, and then is scheduled to close April 26.

The clinic has been the city’s largest single vaccine provider, giving about 185,500 doses since it began March 1, and its efforts make a big difference in how well the city can vaccinate its residents. First doses administered in the city declined by more than a quarter from the week prior when the clinic shifted to second doses only, something city officials said is almost entirely attributable to the shift at the Convention Center.

A second FEMA site in North Philadelphia is scheduled to begin operating Friday but will offer up to 2,500 doses a day, Farley said, about 40% less than the Convention Center site.

“We’d want the site to be able to stay open. It would be a setback if we could not extend it,” said Farley, who said the goal is to vaccinate all Philadelphia’s adults by the end of June. “I think we could probably get there without that site, but the sooner we vaccinate people the better.”

FEMA hasn’t said what it will do, but the city is in discussions with the federal government over FEMA’s presence in the city, Farley said, and Democratic Rep. Dwight Evans is also lobbying.

“We have spoken with FEMA officials and are reaching out to the Biden administration to see what can be done to continue this operation and ensure that as many Philadelphians, particularly those who have not had sufficient access, are able to get vaccinated as quickly as possible,” said Ben Turner, a spokesperson for Evans.

The zip code where the new FEMA site, hosted by the community advocacy group Esperanza, is located has one of the lowest vaccination rates in the city. It also has a majority of Black and brown residents, populations who have been hard hit by COVID-19. Maria Quiñones-Sánchez, who represents the community on City Council, said that she, state legislators, and members of Congress like Evans all played a role in encouraging FEMA to establish its second clinic in the city in that neighborhood.

“The numbers just spoke for themselves,” she said.

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Securing vaccination for the city’s communities of color, many of which also have high rates of poverty, has been an ongoing challenge. The Convention Center FEMA site had been overwhelmingly used by white Philadelphians, though a walk-up option improved the diversity of people getting shots there. A grant from the Centers for Disease Control and Prevention announced Tuesday provided more than $14 million for the city to partner with community-based organizations on vaccine equity. The CDC also granted $101 million to Pennsylvania for the same purpose.

Ambitious outreach is essential to get enough people vaccinated in order to stop the virus’ spread, Quiñones-Sánchez said.

“There’s still too many people playing this, ‘wait and see, I have to wait and see,’ ” she said. “We need to do a better job of getting people to trust us.”

While she would like to see FEMA continue vaccinating Philadelphians at its current rate, relying so much on the Convention Center site wouldn’t be her first choice. The long lines there — though many report that they do move quickly — discourage people who aren’t able to stand a long time. And many Philadelphians don’t live within easy reach of the Center City site. She would encourage the agency to open smaller-scale sites in West Philadelphia and the Northeast.

“We were trying to find a site that got you to that median point of a couple thousand [doses],” she said.

Staff writer Erin McCarthy contributed to this article.