The only reason they work is because we understand evolutionary theory.
Is this really true? I may be wrong but I thought modern vaccine development was based on understanding of how our immune system responds to 'alien' substances such as viruses, bacteria and the plasmodium parasite.
Jenner's first trial vaccination against smallpox was over sixty years before Origin of Species was first published, so clearly the initial work wasn't based on Evolutionary theory (and Pasteur's work was more or less coincident with publication so I doubt that was either).
However, IIRC, one of the co-discoverers of DNA (cant remember the name), eventually decided that aliens planted the first life forms (or something like that), because he understood the DNA and related cellular machinery to be too complex to have arisen spontaneously.
that sounds entirely apocryphal.
Francis Crick was a believer in directed panspermia - as far as I remember he felt it unlikely life had evolved on Earth (don't know why) and proposed that aliens had seeded the Earth in the distant past. He co-authored a paper called Directed Panspermia in 1973.