Non-clinical safety assessment of repeated intramuscular administration of an EV-A71 VLP vaccine in rabbits

A candidate hand, foot, and mouth disease vaccine comprising of human enterovirus A71 (EV-A71) virus-like particles (VLPs) was tested in rabbits to evaluate the potential local and systemic effects of this vaccine. The rabbits received more than double the full human dose and one additional dose according to the n + 1 recommended scheme. The three doses were given mixed with Alhydrogel adjuvant as intramuscular (IM) injections. Vaccinations were well-tolerated, with no indication of overt toxicity in any parameter observed. An EV-A71 specific immune response in the form of antibodies that specifically reacted with the virus capsid proteins VP1 and VP0, the complete VLP, and EV-A71 viruses of different subgenotypes to that of the vaccine could be demonstrated. A boosting effect in the form of higher EV-A71 specific antibody titers was observed after the subsequent doses, and these enhanced titers were shown to be statistically significant in one-way ANOVA analyses. Fortnightly intramuscular administration of EV-A71 VLP vaccine did not result in any test article-related changes in immunotoxicity as defined by increased serum IL-6, and in general IL-6 concentrations remained below the lower limit of quantitation for the majority of animals throughout the study. Although increased indicators of inflammation at the injection site were observed in animals sacrificed immediately after the last vaccination, these largely reversed at the end of the recovery phase. No findings suggestive of systemic or delayed toxicity were recorded in this independently conducted study. In conclusion, repeated IM administration of the EV-A71 VLP vaccine were locally and systemically well-tolerated in rabbits and immunogenic, supporting the clinical development of the vaccine.