Longitudinal and spatial declines in equine Hendra virus vaccination despite continued risk

Hendra virus is an emerging zoonosis endemic to Australia with high fatality of infection in horses and humans. The role of infected domestic horses as amplifying bridge hosts for onward transmission to humans led to the creation of an equine vaccine as a One Health solution against spillover. Despite the risk this disease represents, previously reported equine vaccination rates were low. This study explored vaccination trends between 2012 and 2023 at fine spatial scales and identified demographic and ecological predictors of vaccination against emerging zoonoses. Over 1 million doses of Equivac® HeV were delivered within Australia over this time. The vaccination against Hendra virus has declined since 2014-2015 across both space and time, including within areas of known high risk. Vaccine uptake was highly seasonal, and the density of HeV-vaccinating veterinarians was the strongest predictor of equine vaccination against Hendra virus. While the equine HeV vaccine is highly effective in preventing spillover from bats to horses and thereby protecting people, our results highlight the challenges in sustaining vaccination programs for rare, high consequence pathogens across bridge host populations.