Vaccination and ill-health in dogs: a lack of temporal association and evidence of equivalence.

Following concerns raised over the safety of canine vaccines, an epidemiological investigation was conducted to evaluate the evidence for a temporal association between vaccination and ill-health in dogs. The owners of a randomly selected population of dogs were sent 9055 postal questionnaires, 4040 of which were returned. No temporal association was found between vaccination and ill-health in dogs after adjusting for potential confounders, such as age. However, reliable inferences from non-significant test results are limited and so equivalence-testing methods were also used to make informative inferences. Results demonstrated that recent vaccination (< 3 months) does not increase signs of ill-health by more than 0.5% and may actually decrease it by as much as 5%. This general approach should be used in all field studies of vaccine safety.