The Pentagon has once again mandated influenza vaccinations for military recruits in boot camps across all branches of service, reversing a decision made in April to make the vaccine optional.

A source familiar with the situation stated that the reversal comes amid a growing flu outbreak at the U.S. Air Force’s Lackland Air Force Base boot camp that has sickened nearly 300 personnel. Attorney Aaron Siri noted: “Military reverses course and again mandates flu shots for most military and civilian personnel.”

The Pentagon confirmed that the decision to mandate vaccinations was unrelated to the recent outbreak at Lackland. Only 40% of trainees at Lackland opted for the influenza shot when it was voluntary, according to a source who spoke on condition of anonymity.

In April, Secretary of War Pete Hegseth lifted the mandatory requirement, citing “medical autonomy” and religious freedom, while allowing services up to 15 days to request exceptions. By early May, all military departments had formally requested exemptions for vulnerable populations such as those in communal settings and healthcare workers, which were granted by early June.

Pentagon spokesman Sean Parnell stated that the exceptions were issued following a comprehensive review designed to maximize operational readiness, lethality, and force generation while safeguarding at-risk populations. He emphasized that the decisions were based on thorough risk assessments.

The requirement for influenza vaccines was first mandated in 1945 and remained in effect until April, when Secretary of War Pete Hegseth rescinded it.