From George Washington to World War II, vaccination has been seen as a strategic tool against diseases that could decimate troops. Today, this historical logic is in tension with the rise of individual claims.
For the first time in over 80 years, U.S. military personnel will no longer be required to receive the annual flu vaccine. Secretary of Defense Pete Hegseth announced this change on April 22, 2026. Citing medical autonomy and religious freedom, he described this requirement as “too broad and devoid of rationality,” telling soldiers that “your body, your faith, and your beliefs are non-negotiable.”
The mandatory flu vaccination that Pete Hegseth ended had been in place since 1945, with a brief interruption in 1949. It was part of a tradition of military vaccination requirements almost as old as the United States itself.
As an epidemiologist specializing in vaccine-preventable diseases, I find the end of this mandate more significant for what it reveals than for its immediate effects. Throughout much of American history, military commanders operated on the assumption that infectious diseases could cost them a war, which is why vaccination was seen as part of operational readiness rather than an individual choice.
The first American military vaccination requirement predates the Constitution. In the winter of 1777, General George Washington ordered the mass inoculation of the Continental Army against smallpox.
His decision was not ideological but strategic. The previous year, a smallpox epidemic had devastated American troops near Quebec, contributing to the collapse of the Northern campaign. John Adams wrote to his wife Abigail that smallpox was killing ten soldiers for every one killed in combat.
The scheme persisted for centuries: when an infectious disease posed a greater threat to soldiers than enemy fire, the military enforced protective measures.
U.S. troops were vaccinated against smallpox from the War of 1812 to World War II. During World War I, the army added typhoid vaccination. In World War II, it expanded vaccination requirements to include tetanus, cholera, diphtheria, plague, yellow fever, and, in 1945, the flu.
The mandatory flu vaccination originated from military experiences during the 1918 flu pandemic. This spring, a new flu strain spread in overcrowded military training camps before reaching Europe with American troops. About 45,000 American soldiers died from the flu during World War I, almost as many as those killed in combat.
The pandemic of 1918 showed that a respiratory virus could cripple an army. Therefore, in 1941, as the country prepared to enter a new global conflict, the U.S. Army established a flu commission that teamed up with the University of Michigan to develop the first vaccine against the infection. Clinical trials on recruits showed an 85% reduction in illness incidence, leading to mandatory vaccination in 1945. Approximately 7 million military personnel were vaccinated that year.
The mandate was briefly suspended in 1949 when scientists realized the need to regularly update the vaccine due to virus evolution. Once formulations were seasonally adjusted, the requirement was reinstated in the early 1950s and remained in effect until Pete Hegseth’s policy change.
For decades, vaccination requirements were a routine and uncontroversial part of military life. The Covid-19 pandemic changed that.
In August 2021, all military personnel were ordered to be vaccinated against Covid-19. Over 98% of active-duty soldiers complied, but this mandate became a point of contention. More than 8,000 service members were forcibly discharged for refusing the vaccine.
In 2023, Congress passed a law mandating the Pentagon to lift the Covid-19 vaccine requirement. This shift reshaped the political landscape around vaccination requirements in the military. In January 2025, President Donald Trump ordered the reinstatement, with retroactive compensation, of discharged military personnel.
By announcing the end of the flu vaccine mandate, Pete Hegseth heavily relied on the language of “medical freedom” from the Covid-19 vaccine debates rather than new data on the flu or vaccine efficacy. The medical freedom movement opposes state intervention in what its supporters see as personal health decisions, including public health recommendations like vaccine mandates, mask-wearing, or social distancing.
Critics of the flu vaccine mandate argue that the flu poses a smaller threat today than in 1918, that soldiers are healthier than the general population, and that individual choice should prevail over public health logic for a seasonal virus.
However, epidemiology tells a different story.
Even though the intensity of flu seasons varies, the virus mutates so unpredictably that pandemics like those of 1918, 1957, 1968, and 2009 remain a recurring possibility. The flu continues to cause hospitalizations and tens of thousands of deaths each year in the U.S. The Centers for Disease Control and Prevention estimate that the flu vaccine prevented about 180,000 hospitalizations and 12,000 deaths in the 2024-2025 season.
The military operates under conditions that favor the spread of respiratory viruses: training centers, barracks, ships, or submarines where individuals live in close quarters.
The rationale that led George Washington in 1777 and the Surgeon General of the Army in 1945 to mandate vaccination hasn’t really changed. A sick soldier cannot be deployed, cannot train, and can spread the disease to an entire unit.
What has changed is the political weight given to individual refusal, reflecting more than the vaccine’s efficacy the end of this mandate.
