My old cocker was daignosed at the age of 10.
It can be life threatening and in her case it was. But if the dog responds to treatment then their condition can be managed with medication.
There are various causes and in her case she was treated for the symptoms as it was only after surgery for a lump that it became evident that she was suffering from AIHA.
I believe that in her case the cancer she had (that I was unaware of) triggered off the condition. (as can happen), but many factors can trigger it, vaccinations included.
Hope your dog responds to traetment. There is alot of info on the internet about this condition.
Regards,
From Karen