Why flu shots are back for some US troops

Some military personnel are once again required to receive vaccines in the wake of an outbreak, two months after Pentagon chief Pete Hegseth did away with the 80-year-old mandate.

Chief Pentagon spokesman Sean Parnell told USA TODAY in a statement on Wednesday, June 24, that the Department of the Army, Department of the Navy, Department of the Air Force, National Security Agency and Defense Health Agency had been granted exceptions from the new guidance passed down by Hegseth in April, which made the influenza shot optional.

"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. "The Department remains committed to the health and readiness of our warfighters and civilian personnel."

Hegseth previously announced the suspension of flu vaccine mandates for service members in an April 21 social media post, saying making the shot optional was a move to "restore freedom and strength" to U.S. forces. The flu mandate had been military policy since at least 1945, though vaccine mandates in the U.S. military at large have been documented back to the Revolutionary War.

"We're seizing this moment to discard any absurd, overreaching mandates that only weaken our war-fighting capabilities," said Hegseth. "If you, 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, you should. But we will not force you, because your body, your faith, your convictions are not negotiable."

Vaccine mandate comes amid Air Force flu outbreak

Several reports of an outbreak of flu among recruits at the Lackland Air Force Base, located in San Antonio, Texas, began emerging in mid-June, when the New York Times reported that 160 recruits had fallen ill. The Air Force confirmed the existence of a "localized influenza outbreak among trainees at Basic Military Training" in a statement to USA TODAY on Wednesday, June 24.

"Medical professionals and public health officials have implemented mitigation measures to isolate and treat symptomatic trainees to reduce further exposure and continue to monitor the situation," it said. "Symptomatic trainees are receiving the appropriate care with antiviral medications such as Tamiflu. Once they are cleared by medical professionals, they will return to training.”

The Times reported that uptake of the vaccine had fallen to just 40% after the mandate was dropped, down from what would have been close to 100% based on the previous requirements. For influenza, "herd immunity," which reduces the spread of disease across an entire population, is achieved through a roughly 83% vaccination rate within a community, a much lower rate than other diseases like measles, which requires closer to 95%.

Rep. Joaquin Castro, whose district includes Lackland Air Force Base, said in a June 19 post on X that the Air Force confirmed 222 flu cases at the base as of Thursday, June 18. ABC News reported the same number on Tuesday, June 23, citing people "familiar with the matter." This is compared to 159 total reported cases in 2025, per ABC.

The Air Force declined USA TODAY'S request to confirm these numbers on June 24.

The death of a recruit on the base is also being investigated, the Air Force confirmed, though it is not known if it was related to the outbreak.

One among multiple flu shot changes

The Pentagon's policy was just one among several changes to vaccine recommendations under the Trump administration.

The Centers for Disease Control and Prevention issued a memo in January removing universal recommendations for childhood vaccines that protect against rotavirus, flu, meningococcal disease, COVID-19 and hepatitis A and B. Instead, it said these vaccines are subject to "shared decision-making," a process during which parents consult with health care providers on whether to administer the shots.

A federal judge blocked some of these changes in March, specifically those concerning COVID-19 and Hep B immunizations. HHS has vowed to appeal the decision. In the meantime, the official CDC webpage for the flu, last updated in September 2025, still recommends the flu vaccine for "everyone 6 months and older in the United States, with rare exception."

The most effective way to prevent serious illness from flu is vaccination, according to the World Health Organization, CDC and other leading medical institutions. Currently, the CDC still recommends the vaccine annually for everyone 6 months and older, unless they have a specified medical condition, such as an allergy to its ingredients or a previous severe reaction to the shot. The CDC generally recommends the vaccines be given from September to November, before cold and flu season kicks off, "ideally by October."

Contributing: Kathryn Palmer, USA TODAY