Effects of Feline Herpesvirus Type 1 Vaccination on Clinical Disease, Viral Shedding, and Post-Vaccination Reactions: A Systematic Review and Exploratory Meta-Analysis

Abstract

Feline herpesvirus type 1 (FHV-1) causes respiratory and ocular disease in cats and establishes lifelong latency, but the extent to which vaccination modifies clinical disease, viral shedding, and latency-related outcomes remains uncertain. We systematically reviewed controlled in vivo studies of FHV-1 vaccination in cats, searching PubMed, Web of Science, and the CNKI from inception to 20 May 2026. Risk of bias was assessed with the SYRCLE tool and certainty for core outcomes with the GRADE approach. Exploratory random-effects meta-analyses were undertaken only when outcomes were sufficiently comparable. Of 327 records identified, 23 reports describing 20 independent animal studies (25 cohorts) were included. Fifteen reports evaluated shedding or viral load, 20 assessed immunogenicity, and one companion report examined latency and reactivation. In two comparable challenge studies involving 17 vaccinated and nine control cats, vaccination was associated with fewer post-challenge clinical signs (risk ratio [RR] = 0.64; 95% confidence interval [CI] 0.41 to 0.99). In one monovalent modified-live vaccine study, cumulative clinical scores were lower after vaccination (mean difference [MD] = −36.00; 95% CI −57.25 to −14.75), with Hedges’ g = −1.90 (95% CI −3.52 to −0.27). Estimates for fever, disease-related removal, and post-vaccination sneezing were imprecise. Most virological studies reported lower shedding or viral loads after vaccination, but heterogeneous assays, outcome definitions, and observation windows precluded robust pooling. Antibody responses could not be directly equated with clinical protection. Overall, FHV-1 vaccination may mitigate post-challenge clinical disease, whereas evidence for effects on shedding, post-vaccination reactions, latency, and reactivation remains limited or inconsistent.