A flu outbreak has sickened about 160 Air Force trainees at Joint Base San Antonio-Lackland in Texas, coming weeks after War Secretary Pete Hegseth ended the military's longtime requirement that service members receive annual influenza vaccinations.

"The 37th Training Wing has been managing a localized influenza outbreak among trainees at Basic Military Training," the Air Force said Thursday in a statement obtained by The Washington Post.

Trainees who develop symptoms are being isolated and treated, while medical personnel are also monitoring recruits who may have been exposed.

The Air Force has not revealed whether the infected trainees had received flu shots.

The outbreak comes after Hegseth moved in April to roll back the military's decades-old flu vaccine mandate, calling the requirement "overly broad."

Under the new policy, troops can still choose to receive the vaccine if they believe it is in their best interest.

Hegseth said the change was intended to "restore freedom and strength to our joint force."

The Pentagon has since carved out exceptions for certain military organizations and training environments where leaders believe vaccinations remain necessary to maintain readiness.

Chief Pentagon Spokesman Sean Parnell said the Army, Navy, Air Force, National Security Agency and Defense Health Agency have been authorized to require flu shots in specific circumstances.

"The decisions were based upon thorough risk assessments and are designed to maximize operational readiness, lethality, and force generation, while safeguarding at-risk populations," Parnell said in a statement to the Post.

Last month, Undersecretary of Defense for Personnel and Readiness Anthony Tata told Congress the Pentagon was reviewing exceptions to the voluntary vaccine policy for service members in close-quarter settings such as basic training, submarines, ships and Army Ranger School.

Reports indicate the Air Force received an exception to the policy during the current outbreak, requiring recruits at Lackland to receive flu shots. The service has not publicly confirmed whether that policy has been implemented.

The outbreak is also drawing attention because of the recent death of trainee Keon McDaniel, who suffered a medical emergency during his sixth week of training and was transported to Brooke Army Medical Center.

According to a New York Times report, military officials are investigating whether McDaniel's death is connected to the flu outbreak.

The military first made flu vaccinations mandatory in 1945 after influenza outbreaks had severely affected troop readiness during World War I.

The requirement remained in place for decades before Hegseth's recent policy change, which was part of a broader effort by the Trump administration to scale back military vaccine mandates and give service members greater medical choice.