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

Overview

• This study evaluates the effectiveness of the Hendra virus vaccination schedule in previously unvaccinated mares and their foals, specifically focusing on the antibody response they develop following the recommended prime and boost vaccination regimen.
• The findings show that both mares and foals develop strong Hendra virus-specific antibody responses after completing the vaccination schedule, confirming the effectiveness of the protocol for foals as well as adult horses.

Background

• Hendra virus (HeV) is a highly dangerous virus causing severe respiratory and neurological symptoms in horses and humans, often resulting in high mortality.
• The Equivac® HeV vaccine is designed for horses and is based on a recombinant soluble form of the virus’s G glycoprotein (HeV-sG), which triggers the immune system to produce neutralizing antibodies against HeV.
• Vaccinating horses not only protects the animals but also helps reduce the risk of transmission to humans.
• Foals typically acquire maternal antibodies passively from their vaccinated mothers, which might interfere or modify the effectiveness of their own vaccination responses.
• Current vaccination protocols are optimized mainly for adult horses, and their suitability for foals has been unclear.

Objectives

• To measure HeV-G specific antibody levels in previously unvaccinated mares and their foals at specific time points during the foals’ vaccination schedule.
• To assess whether the existing vaccination protocol used for adult horses is effective in foals.
• To identify the importance of each vaccination dose (especially the third boosting dose) in developing strong immunity in foals.

Methodology

• Selection of previously unvaccinated mares and their foals for the study.
• Administration of the Equivac® HeV vaccine following the manufacturer’s recommended preliminary schedule of three vaccinations (prime and two booster doses).
• Collection of serum samples at key stages of the vaccination process to monitor antibody levels.
• Use of a microsphere-based immunoassay to precisely measure HeV-G specific antibody concentrations in the serum samples.

Findings

• No significant difference was found in the antibody response between mares and foals after vaccination, indicating that foals respond similarly to unvaccinated adult horses.
• Strong HeV-G specific antibody responses were observed in both groups after the completion of all three vaccine doses.
• The third vaccination was critical in eliciting a robust antibody response in foals, confirming the importance of the full prime-boost-boost schedule rather than just the initial doses.
• Foals had little to no passively derived immunity from their mothers since the mares were previously unvaccinated, resulting in limited protection during early life stages.
• This limited early immunity and response to the first two vaccinations potentially leaves foals vulnerable to Hendra virus infection for most of their first year.

Implications

• Vaccination schedules optimized for adult horses are also effective for foals if completed fully.
• It is crucial for foals to complete all three initial vaccine doses to develop adequate protection against Hendra virus.
• There is a window of vulnerability to infection in foals due to the absence of maternal antibodies and initial low vaccine response, highlighting the need for careful management during their first year.
• Ensuring timely vaccination of mares prior to foaling might help provide passive immunity to foals in future settings, which could influence foal vaccination strategies.