Defense Secretary Pete Hegseth announced that U.S. military personnel will no longer be required to receive an annual flu vaccine. He disparaged the long-standing requirement as “absurd, overreaching mandates that only weaken our war-fighting capabilities,” and described his approach as “common-sense.”

If you look at this, either because you know history or have been trained in infectious diseases, you can readily see that his conclusion is flawed.

Infections In The Military

There is a long history of infections occurring in the military, most notably with the 1918 “Spanish Flu.” There, an outbreak in Haskell, Kansas, likely started the global pandemic. In the military alone, there were 45,000 deaths from influenza compared to 53,402 combat deaths. Because of that, and concerns about biological warfare, flu vaccines have been mandated for the military since 1945.

Long before World War I and the 1918 influenza pandemic, the military, under General George Washington in 1777, required vaccination against smallpox , which was decimating the troops. The British troops were unscathed because they had been vaccinated or infected.

More recently, adenovirus outbreaks have occurred at least since 1970, particularly in basic training camps. Up to 80% of acute respiratory infections with fever in recruits are due to adenovirus, resulting in 20% hospitalization rate and some deaths. There was no vaccine available 1999-2011, and cases rose. After the reintroduction of the vaccine, cases again plummeted. The most recent outbreak in 2024 was stopped when the adenovirus vaccine administration was changed from Day 11 to Day 1 of training.

COVID-19 had a notable impact on the military, with leaders and servicemen sidelined by illness and training disrupted. Capt. Brett Crozier asked that 90% of the crew of his nuclear-powered carrier, USS Theodore Roosevelt, be moved into isolation on Guam, after they were stricken with illness. Crozier thought that isolation was impossible on a ship . More than 1200 were infected; one died. He was removed from office for acting unprofessionally in raising the alarm.

Each of these infections is vaccine preventable. Some, such as norovirus, are not.

The Trump administration and Secretary of Health Robert F. Kennedy Jr have a track record of trying to limit vaccines—for COVID-19 , birth dose of Hepatitis B —and by fueling doubt about the safety of the measles vaccine.

This flu season alone caused an estimated 26 million Americans to become ill, per the CDC, with 340,000 hospitalizations and 21,000 deaths . The CDC estimated that 180,000 hospitalizations were prevented by vaccination, as well as 12,000 deaths. This benefit was seen despite this year’s vaccine being a poor match—only 25%-30% effective at preventing the need for medical care.

Intriguingly, one military study of influenza hospitalization rates 2010-2024 showed “ higher hospitalization rates among the youngest age group (<25 years ) of active component service members. This is counter to CDC national data in which adult influenza hospitalization rates increase with each age group.” This would further argue against Hegseth’s decision.

Impact Of Hegseth’s Decision On The Military

The risks to military personnel and preparedness of eliminating mandatory flu and COVID-19 vaccinations can’t be understated. Military personnel work in close quarters where infection control options are limited and, in many cases, ineffective. Deployment to developing countries increases exposure to unsanitary conditions and to waterborne and insect-borne infections.

René Najera, MPH, DrPH, director of Public Health and History of Vaccines at the College of Physicians, said via email, military “leaders have learned the hard way about the impact of communicable disease to troop readiness. Troops living in close quarters are at especially high risk of acquiring and transmitting diseases like influenza, affecting their ability to respond to threats. The flu vaccine, while not perfect, helps prevent or lower incapacitating disease.” Najera added, with the military stretched from Asia to South America, mitigating the risk of carrying a vaccine-preventable disease from one part of the world to another also requires strong vaccine requirements for the troops."

Russell Francis, NP, APRN in Omaha, said via email, “Having cared for both veterans and military personnel over the past 15 years, I've seen how frequent close-quarters living and deployment create high transmission risks, while the extreme physical and mental stresses of their roles can decrease immune responses. Even as young, healthy individuals, service members face higher risk of hospitalization due to these unique occupational exposures, making annual vaccination a critical preventive measure.”

Speaking of vaccinations, Dr. Shane Solger, a former medical officer in the Marines, told me, “There's also research that shows that even in otherwise healthy individuals, it prevents the complications related to the flu. But also, the flu makes people feel sick, so days of work that are lost are days that you are not participating in the military.” He spoke of being cohorted closely in tents, adding that if you are not immunized, “then it's going to spread rapidly and going to make people not be able to do their job.” In response to Hegseth’s comment that eliminating the vaccine requirement is about autonomy and freedom, Solger scoffed, noting that “you're giving up your modicum of your autonomy and your freedom for the greater good, which is defense of the nation.”

Currently, the military vaccinates against almost everything it can—yellow fever, tetanus, typhoid, encephalitis, meningococcus, and more—to either prevent disease during deployments or to protect against the weaponization of flu or other pathogens. Will there be further policy changes that might affect combat readiness?

“Vaccination status is often seen as a surrogate marker for personal political leanings , which is often quite polarizing,” and will undermine a unit’s cohesion and readiness. Deciding to eliminate mandatory flu and COVID-19 vaccinations will only further this division and reduce preparedness.