Animal Medical Hospital

2459 Bellevue Avenue
West Vancouver, BC V7V 1E1


Should Your Pet Be Shot?
The Pet Vaccination Controversy

Cathy Wilkie, DVM

Canine vaccines and duration of immunity

There has been a fair amount of research into vaccine duration of immunity. I have presented the most well-known and what appears to be the most scientifically accurate here.

The Schultz studies and canine vaccines

Starting in the late 1970's Dr. Ron Schultz, now Chairman of the Department of Pathobiological Studies at the University of Wisconsin-Madison, began a series of investigations into the actual duration of immunity of canine vaccines. A summary of his and other studies is presented here:

Minimum Duration of Immunity for Canine Vaccines

Minimum duration of

Method used to
determine immunity

Canine distemper

Rockport strain

7 years / 15 years

challenge / serology

Onderstepoort strain

5 years / 9 years

challenge / serology

Canine adenovirus 2 (CAV2)

7 years / 9 years

challenge / serology

Canine parvovirus 2

7 years

challenge / serology

Canine rabies virus

3 years / 7 years

challenge / serology

Canine parainfluenza

3 years


Bordetella bronchiseptica

9 months


Borrelia burgdorferi

1 year


Canine corona virus

Lifetime (whether vaccinated or not vaccinated)


The gold standard for assessment of immunity is the challenge study. In this type of assessment animals are injected with or exposed to the wild, infective virus and then observed to see whether they develop the disease. Obviously this is not the way we want to test the protection in our pets! This is how vaccines are evaluated in research laboratories.

The other kind of assessment is by serology, or measurement of components in the plasma. For immune status testing we look at antibody production. The presence of antibodies in the blood suggests that the animal has at least generated some humoral immunity. Its limitation is that it does not tell us whether the cell-mediated arm has become involved in the process. As well, we have to establish what level of antibody production is actually protective. At one extreme, a single antibody to canine distemper would constitute an immune response, but that single antibody is not going to protect the dog from an infection. Exactly what concentration of antibodies in the blood is required? That is a question that is yet to be determined for many vaccines, and one of the reasons that serology (titer testing) cannot be used by itself to definitively determine that a pet is immune to a specific disease.

It is very important to note that these results do not imply that all vaccinated dogs will be immune for the period of time listed. It also does not mean that immunity may not last significantly longer, perhaps even for the lifetime of the dog. In the challenge studies for canine distemper, parvovirus and adenovirus, greater than 97% of the dogs were immune to disease after the time period listed.

Other research studies have examined different vaccines and found minimum durations of immunity lasting from a few months to over 7 years. I have included many here for those with access to medical libraries.

Does vaccinating for one component at a time benefit the pet?

There is no data to suggest that this is true. Immunity data and adverse event reports show that the "combination" vaccines give the same level of immunity as single antigen vaccines and have no increased risk of adverse reactions. The suggestion that the combination vaccines somehow "overload" the immune system appears to be unfounded in science.

Additionally, when we vaccinate for a single disease at time we naturally have to give more injections. For instance, if we give canine distemper vaccines and parvo vaccines separately (as opposed to in a combination vaccine) we would need to vaccinate at 8 and 12 weeks for distemper, and 16 and 20 weeks for parvo, or vice versa. That's four injections. With the combination vaccine we give one injection at 8 weeks and one at 12 weeks. That's two injections. Separating the antigens does not increase the immune response or decrease the risk of vaccine reaction, but it does double your cost and time, and means that the pet needs to have more injections. We will discuss below (Vaccine Safety) why we want to minimize the number of injections a pet receives over its lifetime, particularly in cats.





Animal Medical Hospital
2459 Bellevue Avenue
West Vancouver, BC
V7V 1E1
Tel: 604-926-8654
Fax: 604-926-6839

Animal Medical Clinic on Georgia
1338 West Georgia
Vancouver, BC
V6E 4S2
Tel: 604-628-9699
Fax: 604-926-6839

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