Philadelphia’s vaccination rates are significantly lower than the Department of Public Health has been saying, officials acknowledged Wednesday, blaming data errors for the inflated figures.

Most significant, only a third of Philadelphia’s 5-to-11-year-olds have received at least one dose of a COVID-19 vaccine, far fewer than the 53.6% officials have been touting for weeks.

About 26% of the city’s children in that age range are fully vaccinated, the health department announced in a news release Wednesday, the first day children could attend public schools in the city without masks.

Adult vaccination rates also were inflated: Just over three-fourths of Philadelphians 18 and older are fully vaccinated, less than the 82% that had been reported.

“No one is more disappointed than we are at this error, but we have corrected it and instituted new measures to ensure that any future problems are caught before they go live,” said Cheryl Bettigole, the city’s health commissioner.

Bettigole and her top deputies knew the publicly available vaccination rates were incorrect by Feb. 16, spokesperson James Garrow said. Yet they dropped the city’s indoor mask requirement last week before the rates were corrected. Vaccination rates, though, didn’t play a role in changing the rules, Garrow said.

“The reason we didn’t consider it was, as we said throughout the pandemic, the vaccine rate, we don’t have a goal percentage to get to,” he said. “From our perspective, the vaccine rates have nothing to do with our mandates because … we want the mandates to be predicated on what’s actually happening to the virus on the ground.”

Case counts, positivity rates, hospitalizations, and case surges, based on the health department’s recently released system of benchmarks, are the determining factors, he said.

» READ MORE: Far fewer Philly kids may be vaccinated against COVID-19 than the city has said

Garrow acknowledged the data errors won’t help build credibility among city residents already skeptical of vaccination.

“Trust is everything in this business and it’s regrettable that this happened,” he said.

The city has added a second epidemiology team to review data and instituted a monthly overview of vaccination data to accompany the weekly data checks that have been routine. It has also changed the way vaccination rates are presented on the public dashboard to ensure the mistake doesn’t happen again, Garrow said. The raw vaccination numbers on the city’s dashboard have been correct, Garrow said. Just the vaccination rates were wrong.

Ala Stanford, a pediatric surgeon and founder of the Black Doctors’ COVID-19 Consortium, said she wasn’t surprised that the city’s pediatric vaccination rates were incorrect.

“I’ve been at the elementary schools and the high schools since Jan. 18,” she said. “I see the questions that are asked. I see the holes in the education. And I still see some parents who have not endorsed and embraced the idea of vaccination with their children.”

COVID case rates are so low right now she didn’t believe the risk of unmasking at school was significant. But the low vaccination rates among children will be concerning if another COVID surge occurs.

The news comes as children attended city schools unmasked for the first time in almost two years. Making masks optional brought mixed results. At one district high school, a teacher said most of her students were still wearing masks; only about 30% had opted to remove them. At Science Leadership Academy at Beeber, a grades 7-to-12 school in West Philadelphia, virtually everyone kept a mask on. Sanai Browning, a senior, said she saw perhaps 10 students who did not wear masks.

”I kept mine on,” said Browning, 18. “I still like keeping it on. I just like to keep everyone around me safe.”

Elkin Elementary in Kensington asked parental permission before allowing children to unmask. Few families wanted their kids’ masks off, one teacher said.

Bettigole repeated that unmasking is safe.

“The number of people who are testing positive for COVID in Philadelphia is rapidly approaching the lowest we’ve ever seen,” Bettigole said. “Because our case counts are so low, and dropping, we feel that it’s safe enough for people to go unmasked indoors, including in schools.”

The city didn’t provide an explanation of why the adult vaccination rate was incorrect, but said the pediatric vaccination rate became skewed in the process of incorporating data about Philadelphians vaccinated in other Pennsylvania counties earlier this year, Garrow said.

In December, the state shared its records with Philadelphia, leaving the city with hundreds of thousands of duplicated vaccine records. Those were supposed to be accounted for when the data were entered into the city dashboard on Jan. 26, but for 5-to-11-year-olds, they were not. Garrow said he wasn’t sure why that age group alone included duplicate records.

“They just missed it,” he said. “This was a mistake.”

Garrow said he didn’t know when the problem was first identified but said someone noticed the errors during a routine review and it was brought to Bettigole’s attention Feb. 16. The delay in updating the public data was due to an effort to review the data before fixing them.

At that point, Garrow said, the city stopped updating the vaccination rate as new vaccination records came in but didn’t take down the incorrect number while it conducted a review.

» READ MORE: Fractured record keeping leaves Philly hospitals unsure which patients are vaccinated

The health department first acknowledged its review Friday after an Inquirer analysis raised questions about the accuracy of the pediatric vaccination rate.

Coordinating vaccination data has been a headache for public agencies from the start. State, federal, and local record-keeping systems aren’t compatible, and in the absence of a national vaccine database, some data entry is done manually, Garrow said.

“There’s definitely internal frustration here,” he said.

Staff writer Kasturi Pananjary contributed to this article.