From George Washington to World War II: The Historical Context of Military Vaccinations

From George Washington to World War II, vaccination has been considered a strategic tool against diseases that could decimate troops. Today, this historical logic conflicts with the rise of individual demands.

For the first time in over 80 years, U.S. military personnel will no longer be required to receive the annual flu shot. Secretary of Defense Pete Hegseth announced this change on April 22, 2026. Citing medical autonomy and religious freedom, he described this obligation as “too broad and devoid of rationality,” telling soldiers that “your body, your faith, and your beliefs are not negotiable.”

The mandatory flu vaccination Pete Hegseth ended had been in place since 1945, with a brief interruption in 1949. It was part of a tradition of mandatory military vaccinations almost as old as the United States itself.

As an epidemiologist specializing in vaccine-preventable diseases, I find the end of this requirement less significant for its immediate effects than for what it reveals. For much of American history, military commanders assumed that infectious diseases could cause them to lose a war, which is why vaccination was seen as part of operational readiness rather than an individual choice.

A Tradition Dating Back to George Washington

The first American military vaccination mandate predates the Constitution. In the winter of 1777, General George Washington ordered the widespread inoculation of the Continental Army against smallpox.

His decision was not ideological—it was 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 lost in battle.

The 1777 inoculation also carried risks. The procedure, called variolation, involved deliberately infecting a soldier with a small dose of the smallpox virus to induce immunity. George Washington gambled that it was better to lose a few men to inoculation than to lose a war to the virus. Historians credit this decision with saving the Continental Army.

This pattern persisted for centuries: when an infectious disease threatened to incapacitate more soldiers than enemy fire, protective measures were imposed by the military.

American troops were vaccinated against smallpox from the War of 1812 until World War II. During World War I, the military added typhoid vaccination. In World War II, they expanded mandatory vaccinations to also include tetanus, cholera, diphtheria, plague, yellow fever, and, in 1945, the flu.

1945: New War, New Vaccine

The mandatory flu vaccination traces its origins to military experiences during the 1918 flu pandemic. That spring, a new flu strain spread in overcrowded military training camps before reaching Europe with American troops. Around 45,000 American soldiers died from the flu during World War I, almost as many as the roughly 53,000 killed in combat.

The 1918 pandemic demonstrated that a respiratory virus could cripple an army. So, in 1941, as the country prepared to enter a new global conflict, the U.S. Army established a flu commission that partnered with the University of Michigan to develop the first vaccine against this infection. Clinical trials on recruits showed an 85% reduction in disease incidence, and in 1945, the military made vaccination mandatory. Approximately 7 million soldiers were vaccinated that year.

The requirement was briefly suspended in 1949 when scientists realized the vaccine needed regular updates due to virus evolution. Once formulations were seasonally adjusted, the mandate was reinstated in the early 1950s and remained in force uninterrupted until Pete Hegseth’s policy change.

Covid-19 Has Transformed Vaccine Politics

For decades, vaccine mandates were an integral and uncontroversial part of military life. The Covid-19 pandemic changed that.

In August 2021, all military personnel were mandated to receive the Covid-19 vaccine. 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 requiring the Pentagon to cancel the Covid-19 vaccine mandate. This reversal reshaped the political landscape around vaccine requirements in the military. In January 2025, President Donald Trump ordered the reinstatement, with retroactive benefits, of discharged service members.

In announcing the end of the flu vaccination mandate, Pete Hegseth heavily relied on the rhetoric of “medical freedom,” stemming from debates over Covid-19 vaccines, rather than on new data regarding 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.

Does the Justification for Vaccination Still Hold?

Critics of the flu vaccine mandate in the military argue that the flu poses a more limited threat today than in 1918, that military personnel are healthier than the general population, and that individual choice should outweigh public health logic for a seasonal virus.

Epidemiology tells a different story.

Even though the intensity of flu seasons varies, the virus mutates so subtly that pandemics like those in 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 in 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 has, essentially, hardly changed. A sick soldier cannot deploy, cannot train, and can spread the illness to an entire unit.

What has changed, however, is the political weight given to individual refusal, which reflects far more than the question of vaccine efficacy, and that is what is reflected in the end of this mandate.