Are licensed canine parvovirus (CPV2 and CPV2b) vaccines able to elicit protection against CPV2c subtype in puppies?: A systematic review of controlled clinical trials.

Severe gastroenteritis caused by canine parvovirus type 2 (CPV2) is a serious life-threatening disease in puppies less than 4-months of age. The emergence of new variants has provoked some concern about the cross-protection elicited by licensed canine parvovirus modified-live type 2 (CPV2) and type 2b (CPV2b) vaccines against the most recent subtype CPV2c. A systematic review was carried out to assess the efficacy of commercial vaccines. We conducted a literature search of Pub Med/MEDLINE from January 1990 to May 2014. This was supplemented by hand-searching of related citations and searches in Google/Google Scholar. Controlled clinical trials in which vaccinated puppies were challenged with CPV2c virus were evaluated. Reporting of outcome measures and results for vaccine efficacy were critically appraised through a variety of clinical signs, serological tests, virus shedding and the ability to overcome maternally derived antibodies (MDA) titres. Six controlled clinical trials were included in the review. In most cases, the results of the selected studies reported benefits in terms of clinical signs, serological tests and virus shedding. However, MDA interference was not considered or evaluated in 5 of the selected trials. No accurate definitions of baseline healthy status and/or clinical outcomes were provided. Methods of randomization, allocation concealment and blinding were usually poorly reported. As a result of the limited number of included studies matching the inclusion criteria, the small sample sizes, short follow-up and the methodological limitations observed, it was not possible to reach a final conclusion regarding the cross-protection of licensed CPV2 and CPV2b vaccines against the subtype 2c in puppies. Further and specifically designed trials are required in order to elucidate whether cross-protection is acquired from licensed CPV vaccines.