While still the minority, it is still a large number. And a number that should be much smaller as these people are used to doing whatever the government tells them, that’s their job. This is also after all the those who were self declared Trump supporters were forced out. That puts the Biden admin in a very strange position.
Most things in the military is mandatory, and most soldiers comply as resisting would mean discipline or even being kicked out. Mandatory shot lines are a real thing before deployment. Soldiers line up state their name, and get their shot in the line, one after another.
The rumors from inside the military is that there is major pressure inside the service to get the shots and officers are being told if they don’t get it, their career is basically over. So while not mandatory, as that would be illegal for the Biden Admin to do, they are finding other ways to force the shots.
Another rumor from anonymous enlisted servicemen is that the stats are wrong. They claim it is closer to 85% and not 40% who are refusing. Which makes sense as political polls are typically way off. Take the polls that said Hillary would win, or that Biden’s State of the Union received an 85% approval rating. Both of those polls were clearly wrong.