Go read up on the classification of drugs called "biologics". Drug names ending in "-mab" fall into this category. They don't always need a vaxx to do some serious disruption to our immune systems.

I put something on there that is a target for our immune system, a chemical compound with which the immune system is already familiar and to which it is very strongly immune. What you end up with is a drug that will drag this thing to which you are highly immune over to some bacteria you don’t want in your body. And your immune system will attack and kill it.

What happens when this antibiotic attaches to your cells and causes your immune system to target them?