Philadelphia’s least-vaccinated zip codes at the beginning of the summer remain its most undervaccinated now, despite door-to-door outreach, targeted clinics, a lottery, and advertising to encourage people to get COVID-19 inoculations.

As the delta variant spreads, and the threat of other variants looms, these parts of the city are the most vulnerable to serious illness and death.

“Going into the fall, this is going to be a disease of communities that are unvaccinated,” said Marisa Rogers, executive medical director of Oak Street Health, which has a clinic in Fern Rock, which sits in the 19141 zip code with the fewest vaccinations, per capita, in the city. “I think the fall is going to continue to exact a high price on people and communities that are not vaccinated.”

Almost 80% of Philadelphia’s adults have had at least one dose, said Matt Rankin, a spokesperson for the city’s Department of Public Health.

But a closer look shows a dangerous disparity. Five of the city’s zip codes had less than 40% of their residents fully or partially vaccinated as of Aug. 9, according to city data — rates that are on par with Arkansas and Louisiana.

Rankin said things might not be so dire, as it’s possible people are getting vaccinated outside the city. Inoculations are supposed to be recorded according to county of residence, not where the dose was given, but Rankin said the city gets incomplete information about out-of-town vaccinations. He also emphasized that many days thousands of people citywide get vaccinated.

The slow pace of vaccinating these zip codes perpetuates inequities that have grown ever more glaring throughout the pandemic. Only one of the 15 currently least-vaccinated zip codes has a majority white population. Poor communities of color, initially disadvantaged by limited vaccine access in their neighborhoods, are still lagging behind.

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At the current pace, the 15 most-vaccinated zip codes at the start of June would take a little more than six months to reach 80% vaccination, considered a benchmark for widespread protection against the delta variant. The 15 least-vaccinated zip codes would take almost twice as long, just under a year, according to an Inquirer analysis.

The inequities that plague communities of color are part of the reason vaccination has been slow going, said Imani Stewart-Jackson, a spokesperson for Philly Counts, the city organization doing outreach in undervaccinated communities.

“It would be foolish to think that we can quickly undo the actions that have led to well-earned mistrust in these communities,” she said. “We have to show up, listen, and do our best to respond and address access challenges. We knew this work would take time and we are here for whatever it takes.”

The clock is ticking, experts said. Low rates in the fall and winter, as people spend more time indoors, will likely lead to larger case surges, said Rohit Gulati, Einstein Medical Center’s chief medical officer, who is overseeing the hospital’s management of COVID-19 and vaccination. More cases means more opportunities for the virus to mutate and evade vaccines.

“It’s not a matter of if, it’s when it mutates, and how fast it mutates,” Gulati said. “We have to be ready for it, and the only thing for us as a country is to come together.”

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Some of the least-vaccinated zip codes have had the highest hospitalization and death rates throughout the pandemic, city data show. Unvaccinated people who caught and recovered from COVID-19 may have some natural protection against the delta variant. But clinical studies show that protection from vaccination is stronger and longer-lasting than from infection.

This summer, as vaccines became more easily available, the city hosted more than 150 clinics, ranging from all-day events to microsites outside libraries to shots dispensed from a mobile van. For about two months, Philly Counts has knocked on doors and made phone calls in 20 neighborhoods, a list that overlaps with many of the least-vaccinated zip codes in the city. Ads featuring doctors of color aired to win over the reluctant, and a citywide vaccination lottery was weighted to improve the odds for people in the least-protected zip codes.

Hospitals, pharmacies, and community clinics also provided doses throughout Philadelphia.

Outreach efforts have helped push up average vaccination rates in underserved areas by more than 7 percentage points compared with the beginning of June. Success is measured in boosting vaccinations by a handful of people. Stewart-Jackson mentioned a vaccination site in Germantown that was administering just two to four doses an event. After Philly Counts outreach in the community, that increased to 18 per clinic.

“We have seen that layering our outreach with events held by community-based organizations can increase the number of people getting vaccinated,” she said.

But progress in those least-vaccinated zip codes is moving at a pace only a little faster than in zip codes that weren’t targeted. And the gap that continues to divide the least-vaccinated areas from their neighbors is shrinking too slowly to ease the fears of health officials.

Still, chipping away at the city’s unvaccinated population with some small clinics that can offer only slow progress may be the only way to reach hesitant people, said Cornelius Pitts, director of the COVID-19 Vaccination Response Project for Temple University’s Lewis Katz School of Medicine.

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“It sounds like a small number, but it really is meeting people where they are and having one-on-one conversations,” Pitts said. “It’s those one-on-one conversations that seem to turn the tide.”

Unlike in many parts of the country, partisan anti-vaccination sentiment plays little role in Philadelphia’s less-vaccinated zip codes, Rankin said. Misinformation — often through social media — and years of health care distrust are more significant.

“The legacy of racism continues to foster lack of trust in health care and government, including in the vaccine,” he said.

Systemic disadvantages, like poor access to routine health care, can’t be quickly fixed.

“I do think a one-on-one relationship with a provider you trust can help mitigate that distrust,” Rogers, of Oak Street Health, said, “but we also know a lot of folks don’t have those long-lasting relationships.”

And the city’s gun violence plays a role in hampering vaccination efforts.

“We are finding it most difficult in areas that are experiencing high rates of gun violence,” Stewart-Jackson said. “COVID is not the worst thing they are experiencing right now, so we have to meet them where they are, with patience and compassion.”

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In outreach efforts over the last two weeks, Rankin said, only 8% of people said they absolutely would not get vaccinated. That aligns with Gulati’s observations that many unvaccinated people would be willing to get a shot but don’t feel it’s urgent.

“It’s a low-priority task for a lot of people,” Gulati said. “What priority do I give it if I’m healthy and I’m 30? I’ll do it next week.”

Vaccine providers with Einstein recently visited a bar near the Olney Transportation Center and told about 10 people inside, all unvaccinated, that they could get shots immediately at a nearby clinic.

“All 10 of them came down, got their vaccine, and came back” to the bar, Gulati said.

Vaccine apathy is more common in younger people, Gulati said. Just over half of people ages 18 to 44 in Philadelphia have been vaccinated, city data showed, compared with 68% of people 45 to 64, and 77% of those 65 to 74. People likely to be at work during the day, and who rely far more on smartphones and social media for communication, may be harder to reach through typical outreach efforts, though Rankin said door-to-door canvassing has gotten positive results with younger people.

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Reaching younger people, Rogers said, will likely require different approaches than what worked with older populations.

“I wonder if we need to think about ways to engage people, peer networks, influences, people of that age group who have been vaccinated who can share their stories,” she said. “The things that worked early on clearly are not working now.”

City officials are exploring new approaches to reach younger people, Rankin said, including social media ads, a basketball tournament, and outreach at recreation centers.

But the pivot, Rogers said, may be too slow.

“Unfortunately a lot of our public health infrastructure has not been nimble and quick,” she said.

Pitts said COVID-19 itself may prove the best motivator. News of the delta variant could drive people to seek protection.

“We anticipate that people will become frightened,” he said. “Even if you’re not actively listening to the news, by osmosis almost, this is seeping into you in terms of the variants that are emerging.”

Staff writer Chris Williams contributed to this article.