Comparison of antibody and antigen response to intranasal and intramuscular EHV-1 modified-live vaccination in healthy adult horses.
Authors: Stasi Denise, Wagner Bettina, Barnum Samantha, Pusterla Nicola
Journal: Journal of equine veterinary science
Summary
# EHV-1 Modified-Live Vaccine: Route of Administration Matters When neurological EHV-1 outbreaks occur, some practitioners administer the commercially available modified-live vaccine intranasally off-label to exposed healthy horses, hoping to generate rapid mucosal protection before systemic disease develops. Denise and colleagues compared immune responses in three groups of eight healthy adult horses—one receiving intranasal vaccination, one receiving the manufacturer-recommended intramuscular route, and one unvaccinated control—measuring EHV-1-specific antibodies (total IgG, IgG4/7, IgG1, and IgA) in blood and nasal secretions at baseline, 14 days, and 30 days post-vaccination, plus viral DNA shedding via qPCR at day 5. Only the intramuscular group mounted a measurable systemic antibody response, with significant increases in serum total IgG and IgG4/7 by day 14, whilst intranasal vaccination failed to generate detectable increases in either systemic or mucosal antibodies; EHV-1 DNA was detected in nasal secretions for only 48 hours post-intranasal vaccination in just three of eight horses. These findings are particularly important for practitioners responding to outbreaks, as they definitively demonstrate that intranasal administration of this MLV does not deliver the immunological benefit practitioners may assume—making the intramuscular route the only supported option, especially in adult horses with prior EHV-1 vaccination history and existing antibody titres.
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Practical Takeaways
- •Do not administer EHV-1 MLV intranasally to adult horses as an off-label strategy during outbreaks—it does not generate protective antibody responses in vaccinated horses
- •Use only intramuscular EHV-1 MLV administration in accordance with manufacturer guidelines to ensure reliable systemic immunity
- •Intranasal MLV vaccination appears ineffective in horses with prior EHV-1 exposure, likely due to pre-existing antibody interference
Key Findings
- •Intramuscular EHV-1 MLV vaccination induced significant increases in serum total IgG and IgG4/7 antibodies at 14 and 30 days post-vaccination, while intranasal vaccination did not
- •Intranasal vaccination detected EHV-1 DNA by qPCR in nasal secretions for only the first 48 hours in 3 of 8 horses, with no corresponding antibody response
- •Intranasal vaccination failed to generate measurable systemic or mucosal antibody responses in adult horses with pre-existing EHV-1 immunity
- •Intramuscular administration is the manufacturer-recommended and evidence-supported route for EHV-1 MLV vaccination in adult horses