Efficacy of a bivalent inactivated non-adjuvanted feline calicivirus vaccine: Relation between in vitro cross-neutralization and heterologous protection in vivo

Feline calicivirus (FCV) is a major pathogen of the cat characterized by a strong genomic, antigenic and clinical diversity. Despite vaccination, FCV infection is highly prevalent, and for a few years, outbreaks of virulent systemic disease (VSD) have been reported in North America and Europe. An inactivated non-adjuvanted bivalent vaccine was recently developed by combining antigens derived from two broadly cross-reactive FCV strains. The antigenic relatedness between the vaccine strains and other antigenic variants was demonstrated by cross-neutralization studies in vitro. This study showed that vaccine-induced protection against heterologous challenges was correlated to in vitro cross-neutralization, and it validated the use of cross-neutralization tests to select vaccine FCV strains. This correlation applies also for the highly virulent strains causing VSD (VS-FCV).