SALEM — More than half of all Oregonians are now at least partially vaccinated against COVID-19. But demand has slowed in recent weeks, and that’s apparently playing a role in the growing number of wasted doses reported by state health officials.

On Tuesday, May 25, the Oregon Health Authority reported 9,090 vaccine doses have now been wasted, spoiled or expired since December. That’s more than double the total disclosed last week, which stood at 4,418, and it’s more than quadruple the 1,922 reported three weeks ago.

For context, Oregon through May 4 had reported administering nearly 3.1 million doses of vaccine, meaning just 0.06% of doses had been wasted, spoiled or expired.

But since then, Oregon has reported administering 719,665 doses against 7,168 that have been wasted, according to calculations of state data by The Oregonian.

That means that for every 100 doses recently administered, one dose has been wasted — a far higher rate than during the first five months of vaccinations.

Tim Heider, a spokesperson for OHA, said in an email that wastage “may increase as the vaccine rollout continues.” He said that’s because vial sizes for some vaccines have increased, those vials may be opened without every dose being used, and more providers, including smaller sites, are now receiving vaccines.

Heider’s response matches wording from a Centers for Disease Control and Prevention document written last week, which he did not attribute to the CDC.

“CDC and our partners are doing everything possible to minimize the amount of vaccine that goes unused,” the federal document reads.

“We recognize that as we continue to create more opportunities to vaccinate more people, it may increase the likelihood of leaving unused doses in a vial,” the CDC document also said. “While we want to continue to follow best practices to use every dose possible, we do not want that to be at the expense of missing an opportunity to vaccinate every eligible person when they are ready to get vaccinated.”

OHA began regularly disclosing wasted doses in early April, when only 656 doses had been wasted compared to more than 2 million administered.

“We believe that our health system partners are managing their vaccine responsibly and doing everything that they can to minimize waste,” the agency’s chief financial officer, Dave Baden, said in an April 7 statement.

“At this point, considering the logistical complexity of operating large-scale vaccination programs, the small amount of wasted vaccine in Oregon is expected and not surprising,” he added. “This amount is a small fraction of the more than 2 million doses that have been safely delivered, managed and injected in the arms of Oregonians.”