(CNN) For every 850 doses of Covid-19 vaccine administered by March 29, one dose had to be thrown out because it was "unused, spoiled, expired, or wasted," according to data CNN obtained from the US Centers for Disease Control and Prevention.
The CDC records show that 182,874 doses of Covid-19 vaccine were reported as wastage by 35 states, 17 pharmacies and three other federal agencies through March 29. That's less than 1% of the 155 million doses reported administered by that date, and the CDC has stated that some wastage is expected with any vaccine.
However, these figures are likely an underestimate of actual Covid-19 vaccine wastage.
Maryland, for example, is one of 15 states that did not report any vaccine wastage through the CDC's Vaccine Tracking System (VTrckS). Yet, 4,797 doses of more than 4 million administered in the state "were not used and have become ineffective," according to data shared with CNN by the state health department on Wednesday. They were not used because of defective syringes, broken vials and thawed vaccines, including one instance of freezer malfunction. The state is working with a vendor to "resolve issues reporting vaccine wastage to the CDC."
Along with Maryland, other states that did not report wastage through VTrckS include: Alaska, California, Colorado, Kansas, Louisiana, Maine, Michigan, Nebraska, Nevada, New Hampshire, Ohio, Oklahoma and Texas, as well as Washington, D.C. The Ohio health department told CNN in a statement that it is "in compliance with all CDC required reporting."
CDC guidance on Covid-19 vaccination program operations says that Covid-19 doses that were "unused, spoiled, expired, or wasted" should be reported "as required by the jurisdictions' immunization program," but there does not appear to be a federal requirement for this reporting.
Pharmacies accounted for three-quarters of the reported wastage -- about 137,000 doses -- according to the CDC data.
CVS told CNN that "nearly all" of the reported waste occurred while the pharmacy was working with the federal government in administering doses through the federal long-term care facility program. This wastage was "due to issues with transportation restrictions, limitations on redirecting unused doses, and other factors," CVS told CNN in a statement Wednesday. Despite those challenges, waste was limited to about one dose per onsite vaccination clinic, CVS said.
Outside of the federal long-term pharmacy program, CVS said that vaccine waste in retail stores has been "extremely limited," with fewer than 1 in 1,000 doses wasted.
According to the CDC, vaccine wastage can be reported through VTrckS or Tiberius, the system that the US Department of Health and Human Services uses to manage vaccine allocations. The CDC provided data to CNN based on vaccine wastage reported through VTrckS, but notes that "Tiberius would have the most updated vaccine wastage information."