Japan's audit board has requested the health ministry provide supporting documentation for contracts with U.S and British coronavirus vaccine manufacturers after finding a weak basis for ordering a total of 882 million doses in fiscal 2020 and 2021.

The report released Wednesday by the Board of Audit of Japan also found that at least 30 percent of the doses were either canceled or disposed of after expiring.

Photo taken in September 2022 shows Pfizer Inc.'s Omicron-adapted coronavirus vaccine. (Kyodo)

The Ministry of Health, Labor and Welfare spent a total of 4.20 trillion yen ($32 billion) in the two years, with the cost of securing vaccines accounting for 2.40 trillion yen of the amount.

In contracts signed between October 2020 and March 2022, Japan ordered 399 million doses of COVID-19 vaccines from Pfizer Inc., 213 million doses from Moderna Inc., 120 million doses from Astra Zeneca Plc, and 150 million doses from Novavax Inc.

But only around 296 million doses of Pfizer, 83.12 million doses of Moderna, 120,000 doses of AstraZeneca and 290,000 doses of Novavax had been administered as of the end of January.

Of the remaining 500 million doses, the health ministry concluded a contract in February 2022 to cancel approximately 62.25 million doses of the AstraZeneca vaccine and donated around 44.03 million doses as overseas aid.

The ministry said it had also reached an agreement with a supplier of the Novavax vaccine by February this year to cancel around 141.76 million doses.

Meanwhile, around 63.90 million doses of Moderna and 13.50 million doses of AstraZeneca were discarded after expiring. It is not clear how many doses of Pfizer were discarded.

The ministry said it had based its estimates on a simulation that ensured the public could receive the vaccine even if a particular manufacturer failed to deliver. But the audit board criticized the ministry for not including enough validation in its documentation.

"We will take into account the points raised and make improvements when signing future contracts," the ministry said in response.