More than 100,000 Pennsylvanians could be forced to wait days or weeks longer for their coronavirus shots after mistakes made by vaccine providers and possible miscommunication from the state led to a massive shortage of doses, officials said Wednesday.

State health officials said they discovered only last weekend that some providers had been improperly using doses of the two-part Moderna vaccine, giving out their supply of second shots as first doses instead. They said the misuse of second shots had been going on for weeks, though they could not explain exactly why or how it happened, or why it went undetected.

To fix the problem, the state will distribute one week’s worth of second doses over the course of three weeks, officials said, meaning everyone whose appointments are affected by the shortage should be inoculated by mid-March. Pennsylvanians awaiting their second shots should receive them within six weeks of the date they got their first shots. Experts said the delay shouldn’t impact the efficacy of the inoculations.

But the problem, which means tens of thousands of residents will have to wait longer to be fully vaccinated and others may have their first appointments rescheduled, became the newest snag in a distribution process that has frustrated many across the state.

While it won’t impact Philadelphia, which is distributing the vaccine independently, it upended the already difficult process for providers around the region who have been told for weeks by the Department of Health that the supply was secure. In Montgomery County, for instance, 5,729 residents were scheduled to receive their second Moderna doses next week; the county will likely have to reschedule about half of them.

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The shortage also raised questions about state oversight of vaccine providers and tracking of inoculation data. One Montgomery County pharmacist said the temporary shortage would cause chaos.

“We’re going to be spending the next day or two rescheduling,” said the pharmacist, who asked not to be named for fear of repercussions and questioned how the error happened when the state requires all providers to report every shot within 24 hours of administering it. “It’s going to be painful to make those calls.”

The sudden shortage is just one consequence of the scarce national supply of vaccine. As the federal government works to increase supply, Rep. Mary Gay Scanlon said the latest confusion was another symptom of the Trump administration’s failure last year to coordinate a national vaccine distribution.

“This whole building-the-airplane-while-flying — it is just not working well for anyone,” said the Delaware County Democrat.

Discovering the shortage

State health officials would not say which providers made the mistake or how many, why the department did not notice the issue sooner, or how many second-dose shots were given out as first doses.

Spokesperson Barry Ciccocioppo said the problem became apparent when Health Department employees preparing the state’s weekly vaccine request to the federal government realized providers had asked for at least 57,000 more Moderna doses than the state had expected them to request. The state then realized some providers had been misusing the doses for more than a month.

Ciccocioppo said some may have been confused by state guidance or received vaccine shipments that weren’t clearly labeled.

The providers who misused the doses did not realize they were doing anything wrong, acting Health Secretary Alison Beam said, and officials are still trying to trace how it happened. She said “controls” were put in place to ensure it doesn’t happen again, but she didn’t define those steps beyond saying the state would improve communication with providers.

“We are not here to have blame placed anywhere,” she told reporters Wednesday. “In fact, we want to make sure that, instead, all of us are focusing on the path forward.”

State Sen. Maria Collett (D., Bucks and Montgomery) said she agreed with Beam “that pointing fingers is a waste of time” but said the Department of Health needed to address ongoing issues with the rollout, including ensuring a shortage could not happen again.

“The delays, the confusion, the cumbersomeness, the appearance to the general public that things haven’t been fair, and now the discovery of major mistakes like this one, have eroded Pennsylvanians’ trust in the Department’s ability to shepherd us through to the other side of the COVID crisis, which is where we’re all so desperate to be,” she said in a statement.

Vaccine providers will contact anyone whose appointments must be rescheduled, state officials said; anyone who has an appointment and is not contacted should show up as scheduled.

Although the second shots are supposed to be given four weeks after the first shot — and both are necessary to effectively protect against COVID-19 — the Centers for Disease Control and Prevention has said the second doses can be safely administered up to six weeks after the first shot. Everyone waiting for a second shot should receive one within that six-week window, the state said.

“It is not going to mean the vaccine is going to work any less well for them,” said Brianne Barker, a Drew University biologist who studies the immune response to viruses. People waiting for their second doses should continue to take full precautions, she said.

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In Pennsylvania, up to 60,000 second-dose appointments may have to be rescheduled. In addition, up to 55,000 first doses may not be delivered to providers on time, meaning first-dose appointments could be affected as well.

The state’s planned fix should mean nobody misses a second dose and the state’s vaccine allocations will be back to normal by mid-March. Gov. Tom Wolf said he was satisfied with the solution.

“We want to do what we need to do to make sure everyone who gets a first dose has a second dose ready for them,” Wolf said. “And that’s what we did here.”

‘Should have been more clear’

Every week across Pennsylvania, vaccine providers request doses for the following week, asking for first and second doses separately. The state sends those requests to the federal government, which then directs vaccine makers to ship allotments directly to the providers — in separate boxes for first and second doses.

Ciccocioppo said some second-dose boxes delivered to vaccine providers in recent weeks weren’t clearly marked. He also said the Health Department should have been clearer about its guidance: Officials have been telling providers not to hold back first doses to create their own supply of second shots. Ciccocioppo speculated providers may mistakenly have interpreted that as instruction not to hold any doses, including those earmarked as second doses, in reserve.

“We should have been more clear,” he said. “We meant ‘Don’t hold back first doses.’”

Health officials said they could have temporarily suspended first-dose appointments for a week and used those doses to fulfill the scheduled second shots, but said they did not want to cancel all first shots.

“We’re trying to provide the least disruption to people who already have gotten through to their providers and made an appointment for the first dose,” Ciccocioppo said.

Still, it further frustrated local lawmakers and officials who have already asked the state for more transparency and solutions to other rollout problems.

“I was surprised, furious, and disappointed when I got this news because we had been assured repeatedly that those second doses would be there for us,” said Montgomery County Commissioners’ Chair Val Arkoosh, a physician. “This is extremely disappointing.”

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Chester County Commissioner Josh Maxwell said the debacle was more reason for the state to concentrate its vaccine supply on the largest providers, such as counties and hospitals, who might have a better capacity to track doses.

He said the shortage meant vaccination delays for many people in his county, including EMTs, firefighters, and police officers who received their first doses a month ago.

“We’re frustrated,” he said. “We’re just seeing too many of these vaccines get lost in the mix.”

Contributing to this article were staff writers Oona Goodin-Smith, Jason Laughlin, Tom Avril, Rob Tornoe, Marie McCullough, and Ellie Silverman.