Well isn’t that fortunate, seeing as aluminium is only the third most common element in the Earth’s crust and so everywhere you go you’re already exposed to it every day of your life; in the food you eat, in the dust you breathe, in the cuts on your knees from playing in the dirt like a regular child. And, just like every other element/compound (cyanide, lead, water, oxygen, and so on) which your body encounters, Al will have toxic effects at sufficiently high levels, so evolution has developed numerous mechanisms for excreting it before it ever reaches harmful levels.
Ironically, Al is added to vaccines as an adjuvant, thus reducing the amount of antigens needed to provide an effective dose. And the quantity of Al used is tiny; less than what babby is already exposed to through the environment. So you’d think that “vaccine-concerned” parents would be all for something that actually reduces exposure to active ingredients. But as we’ve seen again and again, your average anti-vaxxer doesn’t know biochemistry, epidemiology, and risk-vs-benefit calculations from a kick to the head; though that’s hardly surprising for a bunch of malignant narcissists all pathologically incapable of counting beyond One.