A lack of data makes it “impossible to say” what percentage of Philadelphians who are eligible for a COVID-19 booster shot haven’t gotten one, as the city contends with ongoing challenges capturing the vaccinations of people who cross city lines for their shots.

A data adjustment happening now will soon provide a much better picture of vaccinations, said Philadelphia Public Health Department spokesperson James Garrow. Thousands of people statewide appear to have only one or two doses but, in reality, have the highest level of protection against the coronavirus currently available, city officials believe.

The data difficulties have meant the city and state don’t have fully accurate numbers showing how many need more vaccine doses. And the administration of boosters has further complicated the tracking for the city and state, which run their pandemic responses separately, and worsened the ability to know how many people are partially vaccinated, fully vaccinated, and boosted.

Both the city and state track vaccinations closely and regularly report those data. The problem is their systems don’t automatically link up for people who get doses in and out of the city. So, for instance, someone who got the first two doses in Montgomery County, but got a booster in Philadelphia, is not counted by the state as being boosted and is counted by the city as having only one dose. The opposite is true for someone who originally got vaccinated in Philadelphia and then was boosted outside the city.

» READ MORE: All adults and older teens should get boosters, CDC says. Here’s how to tell if it’s time for an appointment.

People crossing city lines for their vaccines have presented a data collection challenge since vaccination began. The city had been waiting for state records on an estimated 250,000 Philadelphians who have gotten shots elsewhere in Pennsylvania, which the state recently provided. The city, in turn, gave the state data on about 450,000 residents who were vaccinated in Philadelphia.

The detailed data haven’t yet been included in city vaccination records, making for an incomplete picture of key numbers and presenting challenges for officials and organizations allocating resources for vaccine outreach. Philadelphia analysts are working to add the records to the city’s database. They will be added in batches, and the first updates could come in the next week or two, Garrow said.

The state is also incorporating the city’s records into its vaccination data, which cover residents of the 66 other counties, the Pennsylvania Department of Health said.

» READ MORE: More than 200,000 long-awaited state vaccination records could change the picture of who’s had COVID-19 doses in Philadelphia

Health officials anticipate that will raise the numbers both of people who are fully vaccinated and eligible for boosters and those who are boosted. (Fully vaccinated is defined as having two shots of Moderna or Pfizer or one Johnson & Johnson shot.)

“Once we get the state data fully in, we expect the number of boostered people in Philly to jump significantly,” said Garrow.

Data issues have challenged federal, state, and local officials since the pandemic began. Pennsylvania is one of only a handful of states where a major city is running its own vaccine rollout, creating further obstacles. The CDC aimed to speed vaccine distribution by allowing cities like Philadelphia and New York to run separate programs.

Having full vaccine records is key for doing effective outreach to people and communities who need to be vaccinated and knowing where to set up vaccine clinics.

“Not having access to vaccine administration data … makes it more difficult to target our response,” Garrow said. For example, “if someone got one dose of vaccine in the city, and a second one in a suburban county, we don’t know that they need a booster dose.”

More than 2 million Pennsylvanians in the city and state have gotten boosters since Aug. 13, when the first groups became eligible, according to data available from both jurisdictions. The city counts only 169,700 of those in its current records.

Statewide, excluding vaccinations given in Philadelphia, booster demand has been relatively steady for the last few weeks, with more than 360,000 people getting boosters in the two weeks before Thanksgiving and more than 330,000 doing it in the two weeks since.

Nearly a quarter of fully vaccinated Americans have received booster doses, according to federal data. All adults in the country became eligible for boosters on Nov. 19. On Thursday, the CDC and FDA recommended boosters for 16- and 17-year-olds, adding several million teens nationwide to the pool of people who can get the additional dose.

» READ MORE: Pa. COVID-19 hospitalizations are at their highest level since January, with spikes in central and western regions

The holiday season and the emergence of the omicron variant have put boosters in the spotlight in recent days as public health officials have urged people to get the additional protection. Many have sought shots to be safer during holiday travel or gatherings. And preliminary evidence has also indicated that a booster may be necessary to protect against infections caused by omicron.

New Jersey officials went so far as to declare this Wednesday “Boost N.J. Day,” asking clinics to offer additional walk-in spots. More than 1.6 million booster doses have been given in New Jersey in total, representing more than a third of fully vaccinated people.

With cases and hospitalizations rising in Pennsylvania, both officials and hospital leaders last week pleaded with the public to get vaccinated and boosted. Some residents have reported days-long waits for appointments at chain pharmacies, while local officials say city- and county-run clinics have plenty of availability.

“The added protection of a booster is not a bonus,” said New Jersey Gov. Phil Murphy on Wednesday. “It’s a necessity.”