Antigenic differentiation:

Major conserved immunodominant virus-specific antigens on F and HN mean vaccines protect against all isolates.

Minor morbillivirus-specific epitopes on F give some cross-protection between canine distemper, measles and rinderpest. This is why maternally immune puppies were once vaccinated with measles or given human Ig for temporary protection.

Minor variable epitopes to HN, F and NP bind to some but not to other isolates of the same virus species. These have been defined by mAb and separate isolates into binding groups. This is antigenic fingerprinting, and, as with influenza viruses, has been used to track rogue viruses.