A kinetic study of histopathological changes in the subcutis of cats injected with non-adjuvanted and adjuvanted multi-component vaccines.

Abstract The aim of this study was to investigate the subcutaneous tissue response to administration of a single dose of multi-component vaccine in the cat. Three groups of 15 cats were injected with one of three vaccine products with saline as a negative control. Cats in group A received non-adjuvanted vaccine; cats in group B received vaccine with a lipid-based adjuvant; whilst those in group C were vaccinated with a product adjuvanted with an alum–Quil A mixture. The vaccine and saline injection sites were sampled on days 7, 21 and 62 post-vaccination. Biopsies of these vaccine sites were examined qualitatively and scored semi-quantitatively for a series of parameters related to aspects of the inflammatory and tissue repair responses. These data were analysed statistically, including by principal component analysis. At all three time points of the experiment, there was significantly less inflammation associated with administration of non-adjuvanted vaccine ( p  = 0.000). Although there was evidence of tissue repair by day 62 in all groups, those cats receiving adjuvanted vaccines had evidence of residual adjuvant material accumulated within macrophages at this late time point. The severity of tissue reactions may vary significantly in response to vaccines which include adjuvants or are non-adjuvanted.