I have worked with horses for almost 40 years and hepatitis is a real concern. In retrospect, I have seen hepatitis post vaccine administration several times. Some of the cases have been serious but luckily none ended up with death. I had one case where I had to watch the liver enzymes because intermittently the hepatitis would reoccur.
I worked with racehorses, mostly Standardbreds, Trakhaners, Arabians, 1/4 horses, many others. In all my days, I never had, or heard of a horse with Hep. Lucky, I’m sure.