I am a label reader. Whenever I'm thinking about buying food in a box, which is rare, I typically read the whole label to look for sinister ingredients. So when I got a booster vaccine for tetanus last week, naturally I asked for the product information.
Along with a nice dose of tetanus and diphtheria toxoids, my medial deltoid received 0.28 mg of aluminum, up to 0.3 micrograms of mercury, and up to 100 micrograms of "residual formaldehyde". I got the vaccine because I like being able to chew, but I wasn't able to lift my arm for several days. I don't know if that was due to an immune response to the tetanus and diphtheria (probably) or if it was caused by the aluminum, mercury and formaldehyde they injected into my arm.
We work with formaldehyde in my lab, and I can tell you it is not to be messed with. I had to take an entire training course just to use it, during which I learned that if there's enough of it to smell, it's toxic. 0.1 parts per million in the air is enough to cause a burning sensation in the mucous membranes. We always use it in the fume hood. Formaldehyde is a toxin, a carcinogen, and a teratogen (causes birth defects). So I'm sure you'll understand why I wasn't too happy about having 100 ug of it injected into my body.
I'm not criticizing the concept of vaccines, I just wish they'd make more of an effort to clean them up!