Vaccination for the prevention of equine herpesvirus-1 disease in domesticated horses: A systematic review and meta-analysis.
Authors: Osterrieder Klaus, Dorman David C, Burgess Brandy A, Goehring Lutz S, Gross Peggy, Neinast Claire, Pusterla Nicola, Hussey Gisela Soboll, Lunn David P
Journal: Journal of veterinary internal medicine
Summary
# Vaccination Against Equine Herpesvirus-1: Limited Efficacy Confirmed by Systematic Review Despite widespread use of EHV-1 vaccines in equine practice, a comprehensive meta-analysis of 35 peer-reviewed studies reveals that both commercial and experimental formulations—including modified-live, inactivated, DNA, and recombinant variants—provide only minimal protection against clinical disease in naturally infected horses. The review identified substantial heterogeneity across studies and rated the overall quality of evidence as low to moderate, largely due to small sample sizes, methodological underreporting, and inconsistent efficacy findings; several trials even documented no clinical benefit whatsoever. Key outcomes including pyrexia, abortion, neurologic disease, viremia, and nasal shedding showed only modest reductions following vaccination. For farriers and veterinary practitioners managing EHV-1 exposure on yards or in competition settings, these findings suggest that current vaccination protocols should not be relied upon as primary disease prevention; rather, biosecurity measures, isolation of affected horses, and infection control remain the cornerstone of management. The evidence gap warrants urgent investment in next-generation vaccine development and calls for industry-wide re-evaluation of current vaccination recommendations in light of the documented limitations in clinical efficacy.
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Practical Takeaways
- •Current EHV-1 vaccines provide only minimal protection against clinical disease; vaccination alone should not be the sole disease prevention strategy on farms with active EHV-1 exposure
- •Biosecurity and management practices remain critical components of EHV-1 control since existing vaccines show limited efficacy for preventing abortion, neurologic disease, and viral shedding
- •Be cautious interpreting vaccine efficacy claims; the evidence base is limited by small study sizes, heterogeneous methods, and underreported research protocols
Key Findings
- •35 peer-reviewed studies met inclusion criteria from 1018 identified studies, predominantly experimental (31/35) with small sample sizes and moderate risk of bias
- •Eight vaccine subclasses identified: three commercial types (modified-live, inactivated, mixed) and five experimental types (modified-live, inactivated, deletion mutant, DNA, recombinant)
- •Commercial and experimental EHV-1 vaccines minimally reduce incidence of clinical disease, with several studies reporting no benefit or minimal efficacy
- •Meta-analyses revealed significant heterogeneity and low-to-moderate quality of evidence for most outcomes (pyrexia, abortion, neurologic disease, viremia, nasal shedding)