The Pentagon is rushing to administer thousands of remaining flu vaccine doses to military recruits before they expire this week, underscoring the logistical fallout from a policy shift that made annual influenza vaccinations voluntary for most service members earlier this year.

The current supply of seasonal influenza vaccine reaches its labeled expiration date on June 30, the end of the 2025-2026 flu vaccination cycle.

Any doses that remain unused after their expiration date generally cannot be administered and would typically be discarded unless federal regulators authorize an extension.

The looming expiration comes just weeks after War Secretary Pete Hegseth partially reversed his decision to eliminate the military's long-standing flu shot requirement.

Following an influenza outbreak at Joint Base San Antonio-Lackland, home to the Air Force's basic military training program, the Pentagon authorized the military services to once again require flu vaccinations for recruits and other high-risk populations.

Military officials have not disclosed how many doses remain in inventory or how many could go unused before the deadline.

For decades, the War Department vaccinated nearly all active-duty personnel annually, viewing influenza prevention as essential to military readiness. Troops often live, work, and train in close quarters, where respiratory viruses can spread rapidly and disrupt operations.

Hegseth announced in April that annual flu vaccinations would become voluntary for most service members, describing the change as an effort to expand personal medical choice.

The revised approach came under renewed scrutiny after hundreds of recruits at Lackland contracted influenza during an outbreak this spring.

Several trainees were hospitalized, and one recruit died following a medical emergency. Military officials have not determined whether influenza caused the death.

The outbreak prompted military leaders to reinstate mandatory flu shots for incoming recruits, who face a higher risk of transmission because they live in crowded dormitories and undergo intensive training.

The timing created an additional challenge.

Manufacturers produce influenza vaccines on a fixed annual schedule based on strains selected months in advance. As a result, the current season's doses expire before next season's vaccine becomes available, typically in late summer.

That means the Pentagon has only a narrow window to use its remaining supply before it must transition to the 2026-27 vaccine once shipments begin.

The War Department has not publicly estimated the financial impact if expired doses must be discarded, nor has it said whether it expects to purchase fewer vaccines next season in light of its revised vaccination policy.