I believe any vaccine mandates are within the military's discretion. And if they decide to have a booster mandate, you can either follow orders or see yourself out.
COVID-19 booster vaccinations can save tens of thousands of lives in the weeks and months ahead, Biden administration officials said, citing new data that shows the impact of previous shots on hospitalizations and deaths among older Americans. Primary immunizations were associated with up to 680,000 fewer COVID hospitalizations and between 330,000 and 370,000 fewer related deaths among Medicare beneficiaries in 2021, according to research from the Department of Health and Human Services. Prevention of COVID hospitalizations was associated with savings of more than $16 billion in direct costs, the report found. US data shows COVID shots saved at least 330K last year - Tampa Bay Times