For those interested, I found an interesting research paper which seems to indicate that EEHV4 is the most distantly related out of all the strains, which would make it harder to create a cohesive vaccine for I would think. EEHV4 is also one of the rarely reported strains, with only two cases to my knowledge in Europe, whilst this paper also mentions a few in Asia.Since the US vaccine is targeted towards EEHV1A (which Indali at Chester Zoo also survived), I would assume their vaccine is at least targeted towards this strain; but may also target the EEHV4 strain since this has contributed to the death of an adult breeding cow in Chester’s herd.
A small number of lethal and nonlethal cases of viral DNA–positive hemorrhagic disease cases in young Asian elephants involved 2 additional related but considerably diverged species of Proboscivirus (EEHV4 and EEHV5). EEHV4 is estimated to have last had common ancestors with EEHV1 35 million years ago and EEHV5 is estimated to have last had common ancestors with EEHV1 20 million years ago.
Elephant Endotheliotropic Herpesvirus Hemorrhagic Disease in Asian Elephant Calves in Logging Camps, Myanmar - PMC