County spokesperson Fields Moseley said the doses were discarded due to a lack of people to give them to after skipped appointments or due to technical issues such as manufacturing defects or equipment malfunctions.
Moseley said that the discarded doses comprised just 0.3 percent of the 153,196 total doses administered at the five county-affiliated vaccinations sites between December 17 and January 20.
As of Monday, more than 671,000 doses of the vaccine have been administered statewide. More than 297,400 of those have been at Maricopa County sites, and more than 111,000 have been at state-run sites in Maricopa County. However, an overall shortage of vaccines has hampered efforts to ramp up the effort.
Moseley said that the county Department of Public Health and the healthcare systems plan for a percentage of appointments to not show up. Even with the planning, sometimes vials contain extra doses and less people show up than expected.
"This is why administering doses to volunteers and other eligible groups is one of the layers of our plan to minimize waste," Moseley wrote in an email. "Finally, anytime large numbers of vaccines are administered, there is unavoidable waste, in order to maintain a safe operation."
He gave the example of vials without readable labels, bent needles, or inadvertent mistakes by medical staff as cases where wastage could not be avoided.
The number of wasted doses at each site are as follows: Central - 152, Northwest - 134, Southwest - 112, Northeast - 106, Southeast - 49.
The county has since added a sixth site at Grand Canyon University, but it started operation after the window that data was provided for.
The two sites with the highest number of discarded vaccines, central and northwest, are both run by Banner Health, the state's largest hospital system.
To date, 286 doses, or 0.4 percent of the 72,000 administered at Banner sites, have been wasted, said spokesperson Becky Armendariz.
As well as the technical issues Moseley listed, Armendariz added that "weather events" such as wind may occasionally result in waste.
"Banner does everything possible to prevent waste of any vaccine," she wrote in an email. "...Each location manages their end of day process to avoid wastage related to no shows and scheduling by drawing only the needed amounts based on the patients that arrive for their scheduled appointments."
Armendariz did not address Banner's slightly larger number of wasted vaccines, nor did Dignity Health respond to an inquiry about why its southeast site had by the lowest number wasted, but it is possible that the differences could be due to the volume of vaccinations done at the sites. County officials have previously said that the Banner sites had higher demand among healthcare workers during phase 1A than other sites.
As for state-run sites in the county, Arizona Department of Health Services spokesperson Steve Elliott said the state has not wasted any doses at its State Farm Stadium site as far as he is aware of.
Two University of Arizona public health experts reached by Phoenix New Times said that's unlikely.
"The reality is that it's likely there is some wastage," said Dr. Shad Marvasti, the director of the Public Health, Prevention and Population Health theme at the University of Arizona College of Medicine – Phoenix. Marvasti acknowledged that it's possible that the state had learned from other sites to avoid any waste, but that would be unusual.
It's standard for some wastage to occur in vaccination campaigns, even as high as several percentage points, said Dr. Doug Campos-Outcalt, a senior lecturer at the U of A's public health school and a former medical director of the Maricopa County Department of Public Health.
Considering the stringent temperature requirements for the COVID-19 vaccine, he said he's surprised that the county's numbers aren't higher.
"The overall number [of wasted doses] is going to be big, but the proportion is going to be low. I challenge anyone to do better," said Campos-Outcalt.
Elliott did not respond to a follow-up email or text message on Monday afternoon asking for information on how the state defines "wasted" doses.
Wasted vaccines have been a subject of discussion after concerns were raised about people jumping the queue to get jabs. Some have been offered vaccines while driving relatives to get shots at State Farm Stadium, or even volunteered at county sites in the hopes of receiving leftover doses at the end of the day.
State and county officials have defended these practices as a way of ensuring the Pfizer vaccine they use does not spoil after being defrosted and that extra doses in vials do not go to waste. Experts have said it is important to strike a balance between prioritizing those who need vaccines most and ensuring that the vaccination campaign isn't hampered by overly strict guidelines.
Campos-Outcalt said that officials are going to take heat whether they give vaccines to extra people or discard extras.
"At the end of the day you're going to be damned if you do and dammed if you don't," he said.
The important thing, Marvasti said, is to ensure that any wastage is documented and systemically addressed. Investigative nonprofit news outlet ProPublica reported last month that not all vaccine providers are reporting data on wasted vaccines to the Centers for Disease Control and Prevention as required.
Marvasti said that the reporting allows issues to be identified and addressed effectively, but he also hopes state and local officials are doing their own investigations to understand why waste happens and how it can be prevented.
"I'm just hoping we get things right," he said.