The US military is racing to vaccinate new recruits after a two-month halt on mandatory flu shots – but it’s a temporary reprieve, as the shots will soon expire and new doses will not be available for months.
Officials will need to lean on other prevention measures to contain the growing flu outbreak at Lackland air force base in San Antonio, Texas, experts say.
The flu vaccines now being deployed across military basic training camps are set to expire on 30 June, and new doses will not arrive until August or later.
It’s possible military leaders will extend use of the vaccines beyond their expiration date, but that’s “unlikely”, said Toti Sanchez, the former deputy chief at the armed forces health surveillance division of the US Defense Health Agency. And stock of the vaccine is typically low at this time of year as manufacturers switch to making the next season’s doses.
“The earliest that we’ve been able to vaccinate historically has been late August or early September – certainly by the end of September – but I don’t think you can count on them being available before maybe the fourth week of August,” Sanchez said.
“You just can’t change that. The manufacturing timeline is basically etched in stone,” he added.
US military services, including the air force, army and navy, reinstituted flu vaccine requirements for new recruits earlier this week after defense secretary Pete Hegseth removed the mandate at the end of April.
Military leaders have reportedly been working for weeks to reestablish the vaccine mandate, even before the Lackland outbreak sickened at least 275 people and hospitalized four. One recruit, Keon McDaniel, died earlier this month after experiencing a medical emergency. His death is still under investigation, and it’s not yet clear whether it’s linked to the flu outbreak.
When Hegseth announced the mandate would end, he said services would be permitted to ask for exceptions – essentially allowing the mandate to continue – and the decisions to re-implement the requirement are part of that process.
The army is also planning to mandate vaccines for overseas troops, first responders, childcare workers, healthcare personnel, prison staff and soldiers in large-scale training exercises, according to reporting by ABC.
After the mandate was lifted, flu vaccination rates dropped to 40%, which is similar to the wider population. But “basic training is a unique environment”, said Caitlin Rivers, a senior scholar at the Johns Hopkins Center for Health Security and a former civilian epidemiologist for the army.
Boot camp is “famous for being conducive to outbreaks”, Rivers said, calling it a “very vulnerable environment” for the spread of infectious disease. In her 2024 book, Crisis Averted, she detailed the high human cost of infectious disease in the military – and a cycle of “panic and neglect” that has led military leaders to forgo vaccinations and then ramp them up, often at great expense, when outbreaks inevitably occur.
“The flu vaccine is critical to preventing outbreaks and maintaining readiness,” Rivers said.
Recruits are at particular risk because they live in very crowded, close conditions, and they are pushed to their physical limits, under high stress, with little sleep. Younger people in their late teens or early 20s are particularly susceptible to the flu because they haven’t yet encountered many variants of influenza, either through infection or vaccination.
Lackland is the only air force basic training site, which means it draws trainees from around the US and the world. It is currently flu season in the southern hemisphere, and in the US, “flu does circulate year-round – it’s just not common” in summer, Rivers said. “But it only takes one case introduced into Basic for an outbreak to begin.”
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Sanchez likens the conditions to “a petri dish”, and he said leaders are probably “exercising maximum expediency in vaccinating individuals that had not been vaccinated previously” before the end of June.
But about 700 new recruits arrive at Lackland every week, and flu cases are still increasing sharply.
Once the vaccine expires, officials will likely turn to other infection control practices: splitting the recruits into smaller groups for eating and showering; emphasizing handwashing and hand sanitizer. Face masks or respirators may play a role, though they are difficult to train in, and recruits can’t sleep or shower in masks.
When Sanchez heard that the mandate, which was first implemented in 1945, was being overturned, he thought: “Here we are, 81 years later, and we’re turning back the clock.”
He would rather look to the future: specifically to messenger RNA (mRNA) vaccines that may be quickly updated in the face of unusual outbreaks like these.
Moderna is poised to offer the first mRNA flu vaccine for people aged 50 and up – but it could be expanded to other age groups, especially younger adults at high risk like these recruits, Sanchez said, adding: “We could have a platform production manufacturing base using mRNA technology that would allow us to have an updated influenza vaccine within one or two months instead of five to six months.”