MILWAUKEE — 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.”