What worried me was when my youngest son, who’s in the Marines, was about to be deployed to Afghanistan, and he had to get a slew of immunizations. He tells me that he got really sick a few days later, high fever, chills, and nausea. He has no idea what they pumped into him, but it scared me at the time. Thankfully, he got better.
That is not unusual. Some of the things that you are vaccinated with are killed forms of the disease the purpose of which is to trigger the immune system into generating antibodies. So you get the symptoms even though you don't have the disease.
You should be thankful for modern medicine and its mandatory practice in US armed services. In history, soldiers usually died from disease, not enemy action, and their fighting ability while sick was much diminished so even when they died in enemy action you could not be clear it was really from combat or from the fact that they were so weak and weary they could not fight.
Not our modern fighting forces. Death from disease in camp is a rare thing anymore.