NASHVILLE, Tenn. (AP) — Federal officials say a pharmaceutical distributor has agreed to pay $18 million to settle a case over temperature monitors used to ship vaccines under a contract with the Centers for Disease Control and Prevention.

The U.S. attorney’s office in Nashville said on Friday that the government alleged that under the contract, McKesson Corp. was required to ensure vaccines were maintained at proper temperatures by, among other things, setting electronic temperature monitors to detect when air temperature in the box reached certain levels.

According to a news release from the U.S. attorney’s office, the CDC said temperature monitors were a secondary safeguard with other measures also used to ensure appropriate temperatures during shipping.

San Francisco-based McKesson did not immediately respond to an email seeking comment on Friday.

The release said Terrell Fox of Nashville, a former McKesson employee, raised the allegations initially.