I am new to Gear and I only use human products (because I have a couple of them easily available to me and I stick to them).
I am hearing a lot about 'flu like' symptoms.
Many (not all) human beings are allergic to animal proteins and react with similar symptoms (eg tetanus shot that contains horse proteins).
I think that vet products may be contaminated with animal proteins.
If you sterilize a vet product, it will kill germs but will not remove proteins.
Quality standards are much lower as to purification for vet products compared to human products.