Canine distemper is a serious viral disease that affects dogs. It is important to understand that natural distemper is highly contagious and can be life-threatening to dogs. The virus attacks multiple body systems, including the cardiorespiratory system, gastrointestinal system, and eventually the nervous system.

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In New Zealand, between 2021 and 2024, several cases of distemper were reported in unrelated puppies from different households shortly after receiving the Vanguard Plus 5 vaccine, which typically protects against distemper. Vanguard Plus 5 was the most commonly used distemper vaccine in NZ and post vaccinal distemper has been reported in just 0.001% of vaccinated dogs. The affected puppies showed signs of illness within a few weeks of vaccination, which caused concern among both veterinarians and pet owners. Although this condition is extremely rare, in these cases, the illness was linked to post vaccinal distemper caused by the use of a modified live virus distemper vaccine.

The vaccinated dogs that developed distemper, showed some symptoms similar to natural distemper infection (fever, coughing, vomiting and diarrhea). Unfortunately, affected puppies also developed severe neurological symptoms, including seizures which did not respond to treatment. Sadly, these puppies required euthanasia.

Diagnosing vaccine-induced distemper required careful investigation. Veterinarians performed thorough physical examinations and collected samples for laboratory testing. They looked at the timing between vaccination and symptom onset and, in some cases, conducted specialized tests to determine whether the virus involved matched the vaccine strain rather than a wild strain of the virus. In New Zealand, canine distemper is a notifiable disease, and thanks to widespread vaccination, the wild form is now uncommon. However, it remains important to protect dogs in New Zealand through vaccination as the virus can still be found in feral and wild animals, such as cats, ferrets, stoats, seals and sea lions. In 2024, canine distemper virus was also confirmed in fur seals in New Zealand.

While vaccine-induced distemper is extremely rare, these cases highlight the importance of monitoring your dog after any vaccination. It's crucial to understand that the benefits of vaccination still far outweigh the very low risks. Natural distemper infection has a very high mortality rate and outbreaks in unvaccinated dogs can be devastating.

Contact your veterinarian immediately if your dog shows any unusual symptoms after receiving a vaccination. Signs to watch for include:

• Fever.
• Extreme lethargy or unusual tiredness.
• Loss of appetite.
• Eye or nose discharge.
• Coughing.
• Vomiting and/or diarrhea.
• Excessive drooling.
• Any neurological symptoms like seizures, twitching or unsteady walking.

Following these cases, veterinary authorities in New Zealand encouraged enhanced surveillance for vaccine reactions. Vets reviewed vaccination protocols and storage procedures to ensure vaccines were being handled and administered correctly. This helped maintain confidence in the vaccination program while acknowledging the need for careful monitoring of any adverse events. The vaccine associated with the very rare cases of post vaccinal distemper has been withdrawn from sale and close monitoring continues.