the original vaccine was a live virus, and the only way to grow more of it was to infect people and then harvest it from the pox on their bodies. So many generations of this vaccine virus were passed around this way.
For decades everyone believed it was cowpox, another common virus, but after a while scientists noticed it wasn’t actually cowpox - and modern generic studies show that it doesn’t match any known virus
For decades everyone believed it was cowpox, another common virus, but after a while scientists noticed it wasn’t actually cowpox - and modern generic studies show that it doesn’t match any known virus