Comment on the "Report of the AAHA Canine Vaccine Task Force: 2003 canine vaccine guidelines, recommendations, and supporting literature".

Abstract

Dear Editor:The American College of Veterinary Microbiologists (ACVM) was invited by the American Animal Hospital Association (AAHA) to comment on the “Report of the AAHA Canine Vaccine Task Force: 2003 Canine Vaccine Guidelines, Recommendations, and Supporting Literature” (JAAHA,2003;39(March/April):119–131). Dr. Scott McVey, President of ACVM, appointed a committee of ACVM Diplomates (listed on next page) to provide comments on behalf of ACVM.Our committee agrees that decisions regarding selection of vaccines and vaccination interval should be made on an individual basis by a veterinarian with a valid client-patient relationship. The committee also agrees with the concept of designating vaccines as core vaccines, non-core vaccines, and “not generally recommended” vaccines. We emphasize that the final decision on vaccine usage depends on the professional judgment of the veterinarian. Some of the non-core vaccines, such as Leptospirosis vaccines, may be used by a majority of veterinarians, because it is a zoonotic disease with a relatively high prevalence and increasing incidence.1 Other non-core vaccines, such as the Borrellia burgdorferii vaccine, may be rarely recommended because of the low incidence of exposure and clinical disease.Areas of disagreement with the report are some of the statements on duration of immunity and sterilizing immunity. The report states as fact a minimum duration of immunity (DOI) for several of the vaccines based on challenge of immunity and a longer minimum DOI based on antibody titers. For example, the report states that the minimum DOI using antibody titers at levels that provide “sterilizing immunity” are 12 to 15 years for the Rockborn strain of canine distemper virus and 9 years for the Onderstepoort strain. The reader is referred to Table 2 in the report for documentation of these statements. Table 2 states that the estimated minimum DOI for the modified live canine distemper, canine parvovirus-2, and canine adenovirus-2 vaccines is greater than or equal to 7 years. However, the references given in Table 2 are not scientific reports in refereed journals. Sufficient information is not provided in the references to validate the stated minimum DOI. Even if they were well-documented reports of DOI demonstrated in controlled experiments, the results may only apply to dogs and vaccines with characteristics similar to the dogs and vaccines in the study. The DOI may be influenced by vaccine strain and dose, breed, stress, nutrition, age, environment, strain of field virus, and challenge dose. It is incorrect to assume that all dogs will have a minimum DOI equivalent to that reported by the task force. If veterinarians or animal owners believed these statements, they would only revaccinate their dog 7 years or more after the initial vaccine series ending at 1 year of age.The term “sterilizing immunity” is not defined but implies a level of resistance that prevents virus replication. A report from Japan documents that field isolates of canine distemper virus recovered from six clinically ill dogs that had been vaccinated one or more times were antigenically distinct from the Onderstepoort vaccine strain.2 The field isolates were incompletely neutralized by plasma from the dogs that had high neutralizing activity against the Onderstepoort strain. This indicates that there are strain differences in protective immunity and that the immunity is not “sterilizing” immunity.Basing vaccination intervals on the minimum DOI stated in the Report of the AAHA Canine Vaccine Task Force could lead to a decrease in the level of immunity in the canine population, resulting in an outbreak of disease, such as the outbreak of canine distemper that occurred in vaccinated dogs in Finland from 1994 to 1995.3 This outbreak was attributed to a decrease in population immunity to canine distemper virus due to decreased vaccine coverage and frequency, as well as apparent low efficacy of one particular vaccine. The perceptions of DOI in individual dogs may be different when a majority of the general population is vaccinated every year compared to when a majority of the general population is vaccinated every 3 years, as recommended by the Report of the AAHA Canine Vaccine Task Force. With the exception of rabies vaccines, neither the 1-year nor 3-year vaccination intervals are supported by controlled, peer-reviewed studies. Increasing the vaccination interval from 1 year to 3 years for most of the canine population for the “core” viral vaccines seems a reasonable recommendation, given the high level of efficacy observed for yearly vaccination. The veterinary community will need to closely monitor the incidence of infectious disease as the vaccination interval is extended, to ensure that the canine population is not at greater risk of epizootics.Our committee also desires to emphasize the importance of reporting vaccine safety or efficacy problems and recommends that veterinarians report adverse vaccine events to the USDA Center for Veterinary Biologics at the following web site: http://www.aphis.usda.gov/vs/cvb/ic/adverseeventreport.htm