Report: presumed natural or shed vaccine viral exposure in unvaccinated puppies

Once a pup’s residual maternal immunity has waned, he can still maintain measurable levels of immunity, despite being unvaccinated. What are the possible explanations?

Some pet caregivers are reluctant to vaccinate their young puppies for even the more serious communicable infectious diseases, like canine distemper virus (CDV) and canine parvovirus (CPV). Once the residual maternal immunity from the dam has waned, typically at or after 14 weeks of age, families caring for these unvaccinated pups have reported that they remain healthy. In some cases, serum antibody titers have been measured at 12 to 24 weeks of age, and most have some measurable levels of CDV and CPV immunity.

This gives rise to the following question: how do these unvaccinated animals have measurable immunity to these two viruses? Presumably, they have been exposed to low levels of shed vaccine virus from other vaccinates they encountered, and/or experienced natural viral exposure from low amounts in the surrounding area.

To look as this question, a review of our serum antibody testing for CDV and CPV at Hemopet/Hemolife over the prior 18 months revealed the following:

This data shows that six of 62 pups tested for CDV and CPV serum antibodies at four months of age had measurable titers — but only one had very good antibody levels by that age. These results suggest there was some exposure to the natural CDV and CPV viruses, as residual maternal immunity should have been undetectable or low by that time, although this possibility could not be completely ruled out.

Of the 4,181 dogs of all ages that were serum antibody titer-tested, only 0.14% had received no vaccines. Five of the six four-month-old puppies that had not been vaccinated had only adequate serum titers, and so subsequently received one dose of a bi-valent distemper /parvovirus vaccine. All five had developed very good serum antibody titers to both viruses when rechecked a month later.

Further study of unvaccinated puppies is needed, however, because even with the informed consent of their guardians, the risks of viral exposure and illness in unvaccinated puppies creates an ethical dilemma for clinical researchers.


American Animal Hospital Association (AAHA). Canine Vaccination Task Force: Ford RB, Larson LJ, Schultz RD, Welborn LV. 2017 “AAHA canine vaccination guidelines”. J Amer Anim Hosp Assoc.  2017; 47(10): 26-35.

Dodds WJ. “Vaccination protocols for dogs predisposed to vaccine reactions”. J Amer Anim Hosp Assoc. 2001; 38: 1-4.

Dodds, WJ. “Efficacy of a half-dose canine parvovirus and distemper vaccine in small adult dogs: a pilot study”. J Amer Hol Vet Med Assoc. 2015; 41:12-21. Winter Issue.

Dodds, WJ. “Vaccine issues and the World Small Animal Veterinary Assocation (WSAVA) guidelines (2015-2017)”. Israel J Vet Med 2018; 73(2): 3-10.

Twark L, Dodds WJ. “Clinical application of serum parvovirus and distemper virus antibody titers for determining revaccination strategies in healthy dogs”. J Am Vet Med Assoc. 2000; 217: 1021-1024.

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Dr. Jean Dodds received her veterinary degree in 1964 from the Ontario Veterinary College. In 1986, she established Hemopet, the first non-profit national blood bank program for animals. Today, Hemopet also runs Hemolife, an international veterinary specialty diagnostics service. Dr. Dodds has been a member of many committees on hematology, animal models of human disease and veterinary medicine. She received the Holistic Veterinarian of the Year Award from the AHVMA in 1994, has served two terms on the AHVMA’s Board of Directors, chairs their Communications Committee, and currently serves on the Board of the AHVMF, as well as its Research Grant and Editorial Committees.