Federal health officials are turning to Philadelphia to help devise a COVID-19 vaccine distribution plan that could be a model for cities nationwide.

The city, along with four states — California, North Dakota, Florida, and Minnesota — has until Oct. 1 to submit distribution plans to the U.S. Centers for Disease Control and Prevention with logistics for vaccine delivery, data sharing, metrics for effectiveness, and prioritizing who gets the vaccine.

The city received a letter from the U.S. Department of Health and Human Services on Aug. 4 informing officials of Philadelphia’s inclusion in the distribution pilot program. City health officials said they have already started working on plans.

Philadelphia officials, along with those from the four states participating in the pilot program, will work with staff from the CDC and the Department of Defense, the letter states. The plans developed in Philadelphia will be used to shape the federal effort to distribute a vaccine.

COVID-19 has infected at least 5.2 million people in the United States, according to the CDC, and killed 166,317 since January. There is no approved vaccine, and estimates for when there will be one range widely. But it’s not too soon, experts say, to figure out the staggering logistics of getting a COVID-19 vaccine to the people who need it most.

Those could include “people over 65, people at the front line, mass transit, meat packing, pharmacies, grocery stores,” said Paul Offit, a pediatrician and director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

An estimated 120 million people would be among those who would be first in line for a vaccine, he said, and researchers expect each will need two shots, a few weeks apart, to achieve peak immunity.

“There is no precedent for this,” he said.

The people Offit identified as most in need are a third of the country’s 320 million population.

Federal authorities want Philadelphia to include in its planning agencies and professional organizations that will be a part of the distribution process. A key task is determining who should be the highest priority to receive the early doses of the vaccine, how to contact them, and identifying which communities are particularly vulnerable to the virus. A recent study found COVID-19 is killing more than twice as many Black Americans as whites.

Offit noted that just immunizing front line workers and the elderly will require 240 million doses of vaccine, two for each person, and one of the logistical hurdles of the planning process is tracking each of those people, and ensuring they come back for their second dose.

Philadelphia must also plan for the next phase of immunizations as the vaccine becomes more widely available. That includes ensuring providers are enrolled to offer vaccine doses and share data, and coordinating with health care systems treating people at high risk of severe outcomes from the virus because of preexisting health conditions or high risk factors.

Most experts agree that under the best case scenario, a vaccine won’t be available until the first quarter of 2021, but figuring out how to dole out initial supplies could take the better part of a year, Offit predicted. The federal government is seeking to speed the process of mass vaccination through Operation Warp Speed, which includes paying to mass-produce promising vaccine candidates before testing is complete. If the drugs prove to be effective, there will immediately be millions of doses available to ship. That comes with the risk that the government is investing in vaccine candidates that end up being ineffective.

Though some people who oppose or are skeptical of vaccines generally have vowed to avoid a COVID-19 shot, Offit expects the main pressure will come from people desperate to get one. One of the challenges of trying to serve those most in need first, he said, will be people who seek to use money or influence to jump their place in line.

“People of means will probably find a way to get these vaccines,” he said.

The letter to the city explaining the pilot program also gives insight into how the CDC anticipates a vaccine will be distributed.

The CDC will oversee distribution, the letter states, and the doses will be shipped directly to doctors’ offices or drug store chains. Health care workers, long-term-care facility residents and essential workers will be first in line, the letter states. Each will receive two doses of the vaccine separated by 21 to 28 days.

Some of the vaccine candidates will require refrigeration throughout transportation, the letter states.

The federal government expects to provide equipment needed for vaccine distribution, including needles, syringes, masks, and face shields, at no cost. It also anticipates needing to supply satellite vaccination clinics. Curbside and drive-through clinics might be the safest means of distribution for the public and health care providers, the letter states.

The pilot program asks participants to assume limited doses of vaccine would be available this fall. Though that’s far earlier than the most optimistic estimates from scientists, President Donald Trump has suggested he thinks one could be approved by Election Day.

The CDC did not respond to questions about the pilot program, but Offit believed Philadelphia and the four states participating were selected to give the federal agency input from a cross section of environments and demographics.

“A rural district is going to be different than an urban district,” he said. “I think they’re just trying to get ideas of how this is going to get done.”

Pennsylvania’s Department of Health is engaging in similar preparations, including plans for vaccine dispensaries outside hospital or clinical settings, spokesperson Nate Wardle said. Those dispensaries could be in workplaces or congregate care facilities, or at well-known public locations.

“We are working to finalize our vaccination plan and protocols with our partners, including at the federal level, to ensure we are prepared for all aspects of this vaccine,” Wardle said in a statement.

Offit is participating in the state planning efforts, and said governments need to have urgency now to prepare for distribution.

“It’s not premature, no, not at all,” he said. “This is going to be hard enough to do anyway.”