Historical requirements

It remains unclear what strain of flu is circulating in the base. Circulation of seasonal influenza viruses tends to be low during the summer amid the general population. But activity does not fall to zero, and the close quarters and extensive contact within a base make it easy for transmission to skyrocket.

In a statement to Ars Technica, Pentagon spokesperson Sean Parnell said that the Pentagon had granted exceptions to Hegseth’s optional flu shot policy to the Army, Navy, Air Force, National Security Agency, and the Defense Health Agency. The exceptions came after a “comprehensive review” and are in line with a standard policy of “adapting force health protection measures to critical operational realities.”

“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.

With the exception, the Air Force is aiming to vaccinate all recruits at the Texas base, according to ABC News, and the Army is preparing to expand the restored vaccine requirement to other groups, including troops deploying overseas.

US armed forces have a long history with pathogens, beginning in 1777 when George Washington mandated Continental soldiers be inoculated against smallpox, which had ravaged the army during the Revolutionary War. In March of 1918, cases of severe flu broke out at a military base in Kansas. The subsequent 1918 flu pandemic is estimated to have killed around 43,000 US soldiers, nearly half of all US military deaths during World War I.

The US Army supported the development of the first flu vaccine, which was tested for safety and efficacy in military members. The US military issued its first flu shot mandate in 1945, when the vaccine was licensed.