Only one successful vaccination, from what i know. The immune system is aware of the disease and will produce antibodies to fight against the disease if they ever come accross it again. It's just the vets trying to make $$, that's the problem with them being run by private companies - you don't know if the vets telling the truth or lying for your $$
:(.
Also, if you keep having these booster shots, they can BEEEEP up the poor animals immune system.
ALSO, most importantly - do you really think your pet wants to have vaccinations for the rest of their life? i mean, would you like too?
I vaccinate every 3 years. I don't like to vaccinate yearly and if you google there are conflicting opionions.