Vaccination for the prevention of equine herpesvirus‐1 disease in domesticated horses: A systematic review and meta‐analysis

Abstract

BackgroundEquine herpes virus type 1 (EHV‐1) infection in horses is associated with respiratory and neurologic disease, abortion, and neonatal death.HypothesisVaccines decrease the occurrence of clinical disease in EHV‐1‐infected horses.MethodsA systematic review was performed searching multiple databases to identify relevant studies. Selection criteria were original peer‐reviewed research reports that investigated the in vivo use of vaccines for the prevention of disease caused by EHV‐1 in domesticated horses. Main outcomes of interest included pyrexia, abortion, neurologic disease, viremia, and nasal shedding. We evaluated risk of bias, conducted exploratory meta‐analyses of incidence data for the main outcomes, and performed a GRADE evaluation of the quality of evidence for each vaccine subtype.ResultsA total of 1018 unique studies were identified, of which 35 met the inclusion criteria. Experimental studies accounted for 31/35 studies, with the remainder being observational studies. Eight vaccine subclasses were identified including commercial (modified‐live, inactivated, mixed) and experimental (modified‐live, inactivated, deletion mutant, DNA, recombinant). Risk of bias was generally moderate, often because of underreporting of research methods, and sample sizes were small leading to imprecision in the estimate of the effect size. Several studies reported either no benefit or minimal vaccine efficacy for the primary outcomes of interest. Meta‐analyses revealed significant heterogeneity was present, and our confidence in the quality of evidence for most outcomes was low to moderate.Conclusions and Clinical ImportanceOur review indicates that commercial and experimental vaccines minimally reduce the incidence of clinical disease associated with EHV‐1 infection.

Impact of the host immune response on the development of equine herpesvirus myeloencephalopathy in horses

“…Our results highlight the difficulties for vaccine development where young (presumably EHV-1 naive) horses are commonly used. Two recent systematic reviews of the literature show that commercial vaccines can reduce pyrexia, respiratory disease and nasal viral shedding [61,62]. However, there is no evidence that vaccination fully prevents viremia, no evidence that it prevents the occurrence of EHM, and there is limited evidence that killed vaccines reduce the incidence of abortion [10,11,[61][62][63][64].…”

“…Two recent systematic reviews of the literature show that commercial vaccines can reduce pyrexia, respiratory disease and nasal viral shedding [61,62]. However, there is no evidence that vaccination fully prevents viremia, no evidence that it prevents the occurrence of EHM, and there is limited evidence that killed vaccines reduce the incidence of abortion [10,11,[61][62][63][64]. This is perhaps not surprising when considering that vaccines are not tested in age groups where EHM occurs commonly.…”

Updated ACVIM consensus statement on equine herpesvirus‐1

“…Question 1: Does vaccination protect against EHV-1 infection and disease? 10 2. Question 2: Are pharmacologic treatments effective in managing EHV-1 infection?…”

“…16,17 Meta-analyses were also performed to evaluate the efficacy of vaccines for different health outcomes. 10 Additional information regarding the methods and findings of the 4 reviews are available in the individual manuscripts. [10][11][12][13] T A B L E 1 Questions and main conclusions in the 2009 EHV-1 consensus statement.…”

Development of a live attenuated vaccine candidate for equid alphaherpesvirus 1 control: a step towards efficient protection

“…Modified live or attenuated viral vaccines typically elicit robust humoral and cellular immune responses in vaccinated animals, surpassing the efficacy of killed vaccines ( 5 – 7 ). Nevertheless, existing live vaccines for EqAHV1 do not confer comprehensive immunity against the virus and its neurological complications, leading to persistent outbreaks of EqAHV1-related abortion storms and EHM ( 8 , 9 ). Therefore, there is a need to develop more effective live attenuated vaccines.…”