The Department of Defense will no long require annual flu vaccines.

“We are seizing this moment to discard any absurd overreaching mandates that only weaken our warfighting capabilities,” Secretary of Defense Pete Hegseth said Tuesday in a social media post announcing the change.

The flu vaccine mandate for service members has been in place since the 1950s, according to a 2022 medical journal study.

Going forward, service members can choose to receive the vaccine, if they deem it’s right for them, Hegseth said.

Service members who live in congregate settings, such as barracks, are exposed to the respiratory exhalations and secretions of more people who might have the flu than those who live in homes or apartments, said Colorado College Associate Professor Phoebe Lostroh, who holds a doctorate in microbiology. She specializes in pathogenesis, the study of how diseases develop and progress.

“Vaccination protects you even if your neighbor or colleague does not themselves get vaccinated,” she said.

Disease can also be a readiness issue for the military because fighting infectious diseases requires time, personnel and resources like hospital beds, she said.

Perhaps the most stark example is the influenza pandemic that lasted from 1918 to 1919.

About 45,000 U.S. service members died of the disease while the country was fighting World War I, according to the National Guard. For comparison, about 53,400 Americans died during combat in the war.

Vaccination programs in the U.S. military date back to the American Revolution. But they became a contentious political issue during the coronavirus pandemic, when more than 8,400 troops were forced out of the military for refusing to obey the 2021 mandate for the COVID-19 vaccine. Thousands of others sought religious and medical exemptions.

Congress agreed to rescind the mandate, which the Pentagon dropped in January 2023, after roughly 99% of active duty troops in the Navy, Air Force and Marine Corps had gotten the vaccine, and 98% of those in the Army. The Guard and Reserve rates are lower but generally are more than 90%.

The Trump administration then spent months crafting a policy to allow service members who refused to take the mandatory COVID-19 vaccine to reenter service with back pay. While only a tiny fraction have taken the Pentagon up on the new policy, Hegseth’s team has spent the past several months personally highlighting them.

The DOD’s announcement follows the worst flu season in Colorado history, with 5,635 hospitalizations from Oct. 1 through April 11, the most ever, according to the state health department.

The season peaked in December with about 850 people statewide requiring care in a hospital for the flu, department data showed.

Disease transmission is tapering off. As of April 11, hospitals were caring for about 65 people with the flu.

A new strain of the flu made more people sicker this season and required them to seek care medical care, said Hope Shuler, a spokeswoman with the Colorado Department of Public Health and Environment.

Through early April, about 31.2% of Colorado residents had received a vaccine, about .8% lower than the same time last year, she said.

The Associated Press contributed to this report.