It's not really anything about genes of people.
(in cases where it is, they dont really need the vaccine

)
It is the virus types.
I suppose it is vaccine for HIV, not for AIDS - when you get to AIDS (the end result of HIV), theres not much vaccines which would help, unless it would be something which rebuilds the immune system.
In AIDS, patient eventually dies to some rather common disease due to lack of natural immunity, which most, if not all people has against the disease.
The HIV does have different subtypes and on different continents, there can be multiple common subtypes on the same continent.
I don't remember the subtype names or locations, but I do know that US,EU, ASia and Africa does have pretty much different subtypes and a vaccine should be developed specifially for each of them.
