Since the initial identification of canine parvovirus type 2 (CPV-2) [3], there have been a series of mutant variants which have increased in prevalence. CPV-2 was replaced by type 2a [4] and a further variant was then later identified [5]. These CPV mutant variants, CPV-2a and CPV-2b, differ by a single amino acid residue at position 426 of the VP2 capsid protein. More recently, a third mutant variant has been identified [6] called CPV-2c, which also differs from the predecessors by a single amino acid change at position 426. This third variant is becoming increasingly common, having been identified [7] and [8] in a number of European countries and more widespread in Asia [9] and America [10], and shows similar clinical signs to the CPV types 2a and 2b; ranging from mild to severe disease and often death. As the CPV-2 variants differ by only a number of amino acids there has been considerable debate whether vaccines containing a single variant may offer cross protection against the full range. Indeed, vaccination of dogs with vaccines containing CPV-2 strains, or one of its variants, has been shown to cross-protect against virulent heterologous challenge strains [11] and [12]. In addition, we have previously demonstrated [9] that vaccination of dogs with a vaccine containing the CPV-2b strain protects against virulent CPV-2c challenge.