MILWAUKEE (AP) — Some people seeking the newest COVID-19 vaccine are running into high demand, insurance headaches and supply delays coast to coast.

Millions of the newly formulated vaccines have shipped out since the Centers for Disease Control and Prevention signed off on them last week for ages 6 months and up. Cases started rising again in late summer, and experts hope that the new shots will help protect people during the upcoming fall respiratory virus season.

But some people have had to cancel appointments because their insurance hasn’t updated the billing codes to cover the vaccines. Others signed up for an appointment, only to have it canceled due to supply issues. And in some places, there are no available nearby vaccines: A search in Juneau, Alaska, through the federal government’s website shows no available appointments within 100 miles.

Some pharmacies have a limited supply of the shots, Alaska Department of Health spokesperson Alex Huseman said, but order backlogs and slow shipments have prevented the vaccines from being widely available. Private health care providers hopefully can get them as early as next week, she said.

“This rollout has been a little bumpier than anticipated, but we do not believe there will be any significant delay in vaccine availability,” Huseman said.

This is the first time that the vaccines are reaching most Americans through the commercial market, bringing public and private health insurers back in the mix. Previously, the federal government bought and distributed COVID-19 vaccines for free since they became available.

CVS Pharmacy spokesperson Matt Blanchette said some insurers are still in the process of updating their billing systems to cover the vaccines. For others, the shots were covered by insurance without issue, but appointments were canceled by their pharmacy due to supply delays.

Walgreens and CVS confirmed that delivery delays to some stores across the country had led to canceled appointments.

“We are aware of isolated incidences at a small number of locations where appointments had to be rescheduled due to delays in supply,” a Walgreens spokesperson said, noting most stores “have supply to support existing patient appointments.”

Moderna and Pfizer representatives told The Associated Press that they have enough supply. Pfizer spokespeople said it is not experiencing any shortages and has “shipped and delivered several million doses of its 2023-2024 COVID-19 vaccine.” Moderna had six million available as of Thursday, vice president of communications Chris Ridley said.

Marwa Bakr, the owner of a small, private pharmacy on Milwaukee’s southwest side, said she put in a preorder for Pfizer and Moderna’s new vaccines a month ago. She got a call from Moderna this week telling her she should get the vaccines in the next two weeks, and Pfizer has said the shots could come by the end of next week.

She used to order the vaccines through the federal government, and said the return to the commercial process is “taking longer.”

“I receive a lot of phone calls every day from people asking when the vaccine will be available,” Bakr said.

Still, the supply issues aren’t deterring people from looking for the vaccine.

Karen Ramos of Temecula, California, made an appointment at her local CVS as soon as she heard that the vaccines were approved. The 57-year-old insurance underwriter has never had COVID-19 — at least, as far as she is aware. She wanted to keep it that way ahead of a scheduled Caribbean cruise on Oct. 1.

She had scheduled an appointment last Saturday, but the day before, she got a text from the pharmacy saying the new vaccine was not available and her appointment had been canceled. She set a new appointment for Tuesday, which also was canceled “due to unforeseen circumstances.”

Ramos started searching for appointments at any CVS between her home and office in San Diego. By expanding her search to Walgreens, she was able to snag an appointment in Temecula on Tuesday.

“It was frustrating, because I was excited to get it two weeks in advance (of the cruise), and then having to scramble to reschedule,” she said.

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The Associated Press Health and Science Department receives support from the Robert Wood Johnson Foundation. The AP is solely responsible for all content.