Mandatory flu shots for recruits are back across all branches of the U.S. military, the Pentagon confirmed on Wednesday. The reversal comes just two months after Defense Secretary Pete Hegseth made the vaccine optional, and it lands in the middle of a flu outbreak at an Air Force boot camp that has sickened close to 300 people.

A Pentagon official confirmed the change to The Associated Press, though they insisted the decision had nothing to do with the ongoing outbreak at Lackland Air Force Base in Texas. According to the official, who spoke anonymously about details not yet cleared for release, the timing was simply a coincidence.

A Quick Reversal of a Controversial Policy

The shift marks a notable about-face. At the end of April, Hegseth scrapped the longstanding flu vaccine requirement for the military, pointing to “medical autonomy” and religious freedom as his reasoning. But the repeal came with a caveat: individual services were given a 15-day window to request exceptions, meaning they could ask to keep the vaccine mandatory for their recruits.

Those requests were finalized in early June, the Pentagon official said. While the approval happened to coincide with the Lackland outbreak, the official maintained the two events were unrelated.

The numbers, however, paint a stark picture of what happened once the shot became optional. At Lackland, only about 40% of incoming trainees chose to get vaccinated, according to a source familiar with the situation who also requested anonymity.

Why Boot Camps Are Breeding Grounds for the Flu

Lackland processes roughly 700 new recruits every single week, and the close-quarters lifestyle of basic training has long been known to fuel the spread of illness.

Recruits face conditions that are almost tailor-made for transmission:

• High stress and limited sleep over a period of weeks
• Large, open sleeping quarters shared by many trainees
• Communal showers and shared facilities
• Instruction and inspections conducted in tight, close-contact groups

Put simply, when hundreds of people live, sleep, and train shoulder to shoulder, a single virus can move through a population quickly.

The Scale of the Outbreak

The Lackland outbreak has stretched on for about three weeks and produced 275 confirmed flu cases, according to Democratic Representative Joaquin Castro, whose district includes part of the base.

Despite the headline-grabbing number, infectious disease experts say the situation isn’t especially alarming. Dr. Arnold Monto, a flu expert and emeritus professor at the University of Michigan, described the outbreak as “not unusually concerning.”

Monto explained that while flu typically peaks during the late fall and winter, the virus continues circulating at lower levels during warmer months. Concentrated outbreaks in spring and summer do happen, but they tend to cluster in places where large groups gather indoors, such as military bases and cruise ships.

His advice was direct: in group settings like these, vaccination becomes especially important for preventing outbreaks.

Which Branches Requested Exceptions

Sean Parnell, the Pentagon’s top spokesman, confirmed that exceptions were granted to the Army, Navy, and Air Force, along with the National Security Agency and the Defense Health Agency. He declined to share further specifics.

Army and Navy officials have indicated they also sought permission to keep the vaccine mandatory for certain key groups, including:

• Troops preparing to deploy overseas
• Healthcare workers
• Child care workers

These targeted requirements reflect an effort to protect both the most vulnerable populations and those whose roles carry higher exposure or risk.

Advocates Welcome the Change

The reinstatement drew praise from public health advocates. Families Fighting Flu, an advocacy organization, applauded any move to boost vaccination rates.

Michele Slafkosky, the group’s executive director, noted that the military had required flu shots for recruits for decades precisely to protect the health of troops and the public. She called it unfortunate that more than 200 people at Lackland fell ill after that requirement was lifted, and said the updated guidance would ultimately save lives.

For now, the policy has come full circle. After a brief experiment with optional vaccinations, the military is once again requiring recruits to roll up their sleeves, just as an outbreak underscores why that rule existed in the first place.

This article touches on health and vaccine policy, which can be a sensitive subject. Anyone making decisions about their own vaccinations should consult a qualified healthcare provider for guidance tailored to their situation.