Investigation of the Systemic Antibody Response and Antigen Detection Following Intranasal Administration of Two Commercial Equine Herpesvirus-1 Vaccines to Adult Horses.
Authors: Spann Kennedy, Barnum Samantha, Pusterla Nicola
Journal: Journal of equine veterinary science
Summary
# Editorial Summary When emergency intranasal EHV-1 vaccination is deployed during outbreak situations, practitioners face a critical diagnostic problem: distinguishing vaccine-derived virus shedding from genuine infection becomes difficult if recently vaccinated horses subsequently develop clinical signs. This 2023 investigation by Kennedy and colleagues compared two commercially available intranasal EHV-1 vaccines—Rhinomune (modified-live) and Calvenza (inactivated adjuvanted)—to evaluate both their systemic immune efficacy and nasal shedding profiles in 30 unvaccinated adult horses. Neither vaccine induced measurable systemic antibody responses (total Ig or IgG4/7) 30 days post-vaccination, yet both generated detectable viral nucleic acid in nasal secretions: 9 of 10 horses vaccinated with Rhinomune and 8 of 10 receiving Calvenza tested qPCR-positive for EHV-1 within 1–3 days, with no significant difference between products in shedding duration or viral load. These findings highlight a substantial practical challenge for outbreak management—the majority of intranasally vaccinated horses will shed vaccine-derived virus for several days, potentially confounding diagnostic interpretation when qPCR is used to confirm active infection during emergency responses. Clinicians should therefore consider delaying diagnostic sampling by at least 3–4 days post-intranasal vaccination or relying on clinical and serological assessment rather than nasal qPCR alone when recently vaccinated horses present with compatible signs during outbreak investigations.
Read the full abstract on PubMed
Practical Takeaways
- •Intranasal EHV-1 vaccines do not generate systemic antibody protection in adult horses, which may limit their effectiveness during emergency outbreak protocols—consider alternative vaccination strategies or routes for at-risk populations
- •Recently vaccinated horses will shed detectable EHV-1 RNA nasally for 1-3 days; clinicians must account for this when interpreting qPCR results during outbreaks to avoid misdiagnosing vaccine virus as clinical infection
- •Both commercial intranasal vaccines perform similarly regarding viral shedding and lack of systemic immunity, so choice between them should be based on other factors such as availability and cost rather than perceived immunological superiority
Key Findings
- •Intranasal administration of both Calvenza (killed-adjuvanted) and Rhinomune (modified-live) EHV-1 vaccines failed to induce measurable systemic antibody response (total Ig and IgG4/7) at 30 days post-vaccination compared to unvaccinated controls
- •Vaccine-derived EHV-1 was detected by qPCR in nasal secretions in 9/10 horses receiving Rhinomune and 8/10 horses receiving Calvenza, persisting for 1-3 days post-vaccination
- •No significant difference in qPCR detection rates or viral load quantitation between the two vaccine types
- •Intranasal vaccine-derived viral shedding may complicate diagnostic interpretation of EHV-1 infection during outbreak situations in recently vaccinated horses