Many vaccines are from injecting a virus into and egg and extracting the vaccine from said egg later.
A new flu vaccine system come from a dogs kidney. The weird part (I kid you not, I heard about this on NPR) the dogs kidney in question come from a single cocker spanniel, harvested in the 1950's. These cells are referred to "immortal cells) because they can treat the cells like a culture and keep it growing, and then cut off bits for use.
Anyway, a lot of medications are tested on animals, but some are actually made using animals. What's the vegan stance on polio, flu, and other vaccines?