(CNN) As a repeal of the US military's Covid-19 vaccine mandate took a step closer to becoming law on Thursday, military officials and experts are warning it's a change that could have adverse ripple-effects on military readiness and the ability of service members to deploy around the world.
"This isn't just our side of the equation," a defense official told CNN regarding the possible impact of the change. "It's what our partners and people that we would train and work with are asking us to do to enter the country."
The National Defense Authorization Act (NDAA) released on Tuesday includes a provision that would rescind the Pentagon's current mandate requiring troops receive the Covid vaccine. And while Republican lawmakers have celebrated its inclusion, the White House said it's a mistake -- though President Joe Biden has not made clear if he will sign the bill with the included provision in it.
The House passed the NDAA on Thursday in a 350-80 vote.
Deputy Defense Press Secretary Sabrina Singh declined on Wednesday to go into detail about what the Pentagon was preparing for if the mandate was repealed, instead emphasizing that Defense Secretary Lloyd Austin believes the mandate is important for the health of the force.
"What is important to the readiness of the force is getting the vaccine," Singh said. "So yes, it would impact the readiness of the force -- you're more prone to getting Covid-19."
It's not just about the US. American troops often have additional vaccine requirements depending on the area of the world to which they are deploying or being rotated through. Under the Pentagon's current policy, service members who have not gotten the vaccine are considered non-deployable, Singh said Wednesday.
Indeed, retired Gen. Robert Abrams, who previously commanded US troops in South Korea, told CNN that the vaccine repeal "will make our job more difficult," referring to the duties of overseas commanders. The Covid-19 vaccine is required for entry to South Korea and Japan -- countries that host thousands of US service members.
Repealing the vaccine mandate "will put the US forces in an awkward position," Abrams said, because "the host nation expects us to follow their regulations (and SOFA [status of forces agreement] requires it)."
Republicans have long railed against the Covid vaccine requirement -- which is one of more than 15 required vaccines, depending on where a service member is deployed.
An August 2021 policy signed by Austin required all service members to receive the vaccine; the services set their own deadlines for when their troops had to be fully vaccinated.
Now, roughly a year later, the vast majority of US troops are: 97% of active duty soldiers are completely vaccinated, as are 99% of active duty airmen, 96% of active duty Marines, and 98% of active duty sailors.
But as the military faces the biggest recruiting crisis in decades, critics of the mandate say it is pushing out willing service members at a time when the military needs them most and standing in the way of recruits who want to join but do not want to get the vaccine.
Marine Corps Commandant Gen. David Berger said over the weekend that the mandate is having an impact on recruiting, specifically "in parts of the country there's still myths and misbeliefs about the back story behind it." Capt. Ryan Bruce, a Marine Corps spokesman, later told CNN Berger was referencing "anecdotal conversations" he has had with recruiters, and not specific data showing an impact of the mandate on recruitment.
Officials and experts raised other concerns, however, about the impact repealing the mandate could have on troops already in uniform. Rachel VanLandingham, a retired Air Force judge advocate and law professor at Southwestern Law School, told CNN that there could be "ripple effects" for units if some service members are unable to deploy because of the vaccine.
That is especially notable for smaller units, like those found in the special operations community. While conventional forces may be able to ensure they have the numbers they need for a deployment or rotation, smaller units could face more of a challenge if the few people they have are unable to deploy because of a vaccine requirement.
"If one unit can't go, then the unit they're replacing, they don't get to go home on leave ... It's not just one unit and one person," VanLandingham said. "One person's inability to show up to work in a military unit affects that entire unit, and that unit is depended on by other units. It is truly a team dynamic."
Abrams also pointed out that vaccinations "help prevent serious illness," and US Forces Korea "does not have the medical capacity to handle a large number of very sick infected personnel." Instead, US personnel would have to be sent to Korean facilities, he said, which could raise issues if there is a lack of availability or if the facility is not approved by TRICARE, the US military's health care provider.
Experts also raised questions about the precedent it would set to roll back a lawful military order after so many refused to follow it.
"If I'm a commander, what concerns do I have about managing this person who failed to comply with a lawful order?" said Kate Kuzminski, the director of the Military, Veterans, and Society Program at the Center for New American Security.
"I think there are some bigger challenges within the social context and the culture of the military if pushing back on a lawful order actually changes the nature of the lawful order," she added. "You might see people refusing to do other things in the future that we very much need them to do."
Among the debated points of the vaccine repeal is the question of what will happen to the roughly 8,000 service members who have already been separated and forced to leave the military because they refused to be vaccinated. While some speculate that because they refused a lawful order they will remain separated, some lawmakers are pushing for them to be reinstated.
A letter sent on November 30 to Republican leadership and signed by 13 Republican senators requests that not only is the mandate rescinded, but that service members who have been separated are reinstated "with back pay." Pentagon leaders are reportedly discussing the possibility.