Policy Change and Initial Outbreak
"If you are an American Warrior entrusted to defend this nation, believe that the flu vaccine is in your best interest, then you are free to take it... But we will not force you, because your body, your faith and your convictions are not negotiable." — Defense Secretary Pete Hegseth
On April 21, 2026, the Department of Defense made the annual flu vaccination optional for all active duty, reserve component, and civilian personnel, ending a mandate that had been in place since 1945. Defense Secretary Pete Hegseth described the previous mandate as "overly broad" and "not rational."
The flu vaccine had been required for U.S. military personnel since 1945, with a brief withdrawal in 1949 before reinstatement in the early 1950s. The U.S. Army originally developed the first flu vaccine at the start of the Second World War, motivated by concerns over the 1918 influenza outbreak's impact on military readiness.
Following the policy change, the flu vaccination rate among recruits at Joint Base San Antonio-Lackland, Texas, dropped from nearly 100% to approximately 40%. The base processes roughly 700 new recruits weekly.
Scale of the Outbreak
Multiple sources reported that the outbreak at Lackland Air Force Base sickened between 159 and 300 trainees. Recruits live in communal settings—shared dormitories and dining facilities—which are known to be vulnerable to outbreaks of airborne illnesses. Reports from different dates cited:
- 159 cases and two hospitalizations as of an early date
- At least 222 recruits ill and four hospitalized as of June 23
- At least 275 sickened since early June, according to Representative Joaquin Castro (D-TX)
- Nearly 300 people, according to a Pentagon official
An Air Force spokesperson confirmed a "localized influenza outbreak among trainees at Basic Military Training."
Reinstatement of Vaccine Mandate
The Pentagon had allowed military services to request exceptions to the new policy within 15 days of its enactment. The Air Force submitted an exception request on May 5 to reinstate the vaccine requirement for recruits at Lackland.
The exception was approved on June 11 by Anthony Tata, Pentagon undersecretary for personnel and readiness. Base officials reportedly did not learn of the reinstatement until June 18.
Pentagon Chief Spokesman Sean Parnell stated that the decisions to grant exceptions were based on "thorough risk assessments and designed to maximize operational readiness while safeguarding at-risk populations." Parnell confirmed that exceptions were granted to the Army, Navy, Air Force, National Security Agency (NSA), and Defense Health Agency (DHA), allowing them to require the vaccine in certain cases.
A Pentagon official stated that the permission to mandate vaccinations was unrelated to the outbreak, noting the exceptions were being finalized in early June; the timing with the Lackland outbreak was coincidental. Following the reinstatement, Air Force officials ordered recruits at Lackland to be vaccinated against the flu as part of containment efforts.
Containment and Response
Mitigation measures implemented at the base include isolation and treatment of symptomatic trainees with antiviral medications such as Tamiflu, as well as monitoring of close contacts. An Air Force spokesperson said symptomatic trainees "are receiving appropriate care."
Army and Navy officials have said they asked for permission to mandate the shot for troops deploying overseas, healthcare workers, and child care workers.
Related Incident
The cause of a recent medical emergency on June 16 that led to the death of basic trainee Keon McDaniel is under investigation. It is not yet clear whether the death is related to the flu outbreak.
Context and Expert Commentary
"The outbreak is not unusually concerning... flu viruses circulate at lower levels in warmer months and concentrated outbreaks can occur in group settings like military bases." — Dr. Arnold Monto, flu expert at the University of Michigan
A 2024 study by the Defense Health Agency found that from 2010-2011 to 2023-2024, the highest rate of influenza hospitalizations among active service members was among those under 25, especially young recruits.
The policy change and subsequent outbreak follow a period of significant vaccine policy shifts for the military:
- Between 2021 and 2022, approximately 8,000 service members were separated from service for refusing the COVID-19 vaccine.
- The Pentagon rescinded the COVID-19 vaccine mandate in September 2023.
- An executive order signed by then-President Donald Trump in January 2025 allowed service members discharged for refusing the COVID-19 vaccine to return to service with no impact on their status, rank, or pay, provided they submit a written attestation.