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

Overview

• This study examines trends in vaccination of horses against Hendra virus in Australia from 2012 to 2023.
• It highlights a decline in equine vaccination rates despite ongoing risk of infection to horses and humans.

Background on Hendra Virus and Vaccination

• Hendra virus (HeV) is a zoonotic virus endemic to Australia, meaning it can be transmitted from animals to humans.
• The virus has a high fatality rate when it infects horses and humans.
• Infected domestic horses serve as “bridge hosts” that amplify the virus and facilitate transmission to humans.
• To reduce spillover from bats (the natural reservoir) to horses and thereby protect humans, an equine vaccine called Equivac® HeV was developed.
• This vaccine forms part of a One Health approach, considering interconnected health of animals, humans, and the environment.

Study Purpose and Methods

• The research aimed to analyze vaccination trends over an 11-year period (2012-2023), focusing on spatial (geographical) and temporal (time-related) changes.
• It also sought to identify factors influencing vaccine uptake, especially demographic and ecological predictors.
• More than one million doses of the vaccine were administered during the study period throughout Australia.

Key Findings

• There was a notable decline in equine vaccination rates starting after 2014-2015, across different regions, including areas considered to be at high risk for Hendra virus.
• Vaccination uptake showed marked seasonality, indicating times during the year when vaccination rates were higher or lower.
• The density of veterinarians who administer the HeV vaccine was the strongest predictor of vaccination rates, implying that access to vaccinating veterinarians influences vaccine coverage.
• This suggests that logistical factors and healthcare access play important roles in vaccine uptake for disappearing but serious diseases.

Implications

• Although the equine vaccine is highly effective in preventing transmission from bats to horses, and thus indirectly protecting human health, maintaining sustained vaccination coverage remains challenging.
• Declining vaccination rates raise concerns about ongoing vulnerability to Hendra virus spillover events despite the vaccine’s availability and effectiveness.
• The findings emphasize the difficulty of sustaining vaccination programs against rare diseases that have high consequences when they occur but may be perceived as low risk by horse owners or veterinarians over time.
• These insights could inform future strategies to improve vaccine uptake, possibly by increasing veterinarian availability or public awareness in high-risk areas.

Conclusion

• This study provides valuable longitudinal and spatial data on equine Hendra virus vaccination trends in Australia.
• It highlights the necessity of addressing ecological, demographic, and healthcare delivery factors to enhance sustained vaccination uptake for zoonotic diseases involving animal bridge hosts.
• Addressing these challenges is critical from a One Health perspective to prevent zoonotic spillover events and protect both animal and human health.