Vaccination against Hendra virus of previously unvaccinated mares and their foals demonstrates the effectiveness of the current prime and boost vaccination schedule for foals

Hendra virus (HeV) is a high consequence pathogen that causes severe respiratory and/or neurological disease in both horses and humans with high mortality. The equine vaccine, Equivac® HeV, is a recombinant soluble version of the G glycoprotein of HeV (HeV-sG) that elicits a potent HeV-neutralising antibody response in adult horses and also provides indirect protection for humans. Maternally derived HeV-G specific antibodies could interfere with subsequent foal vaccination, although other factors such as foal age and the suitability of vaccination protocols that have been optimised for adult horses may also be important. The aim of this study was to measure the HeV-G specific antibody levels of previously unvaccinated mares and their foals at key time points during the preliminary HeV vaccination schedule of three vaccinations. Previously unvaccinated mares and their foals were vaccinated according to the manufacturers recommendations and serum samples were tested for HeV-G specific antibodies using a microsphere-based immunoassay. There was no difference in the humoral response to vaccination between the mares and foals, and both mare and foal groups demonstrated a strong HeV-G specific antibody response after completion of the preliminary vaccination schedule. This study highlights the importance of the third vaccination in eliciting a strong antibody response in foals, as has been demonstrated previously for adult horses. However, the absence of passively acquired immunity and the limited response of foals to the initial two vaccinations does leave foals vulnerable to infection during the majority of the first year of life.