Effect of dexamethasone on antibody response of horses to vaccination with a combined equine influenza virus and equine herpesvirus‐1 vaccine

Abstract

AbstractBackgroundDexamethasone is routinely administered to horses but its effect on the antibody response to a commercial EIV/EHV vaccine is unclear.HypothesisHorses receiving dexamethasone will have lower postvaccination antibody levels against EIV and EHV‐1 than vaccinated controls.AnimalsFifty‐five healthy adult research horses.MethodsRandomized cohort study. Control (no vaccine, group 1), vaccination only (EIV/EHV‐1/EHV‐4, Prestige 2, Merck Animal Health, group 2), vaccination and concurrent single intravenous dose of dexamethasone (approximately .05 mg/kg, group 3), vaccination and 3 intravenous doses of dexamethasone at 24 hours intervals (group 4). Serum SAA levels were measured on day 1 and day 3. Antibody levels against EIV (hemagglutination inhibition assay, Kentucky 2014 antigen) and EHV‐1 (multiplex ELISA targeting total IgG and IgG 4/7) were measured on day 1 and day 30.ResultsSignificantly increased mean antibody titers after vaccination were only noted against EIV and only after the vaccination alone (n = 14, prevaccine mean [prvm] 166.9, SD 259.6, 95% CI 16.95‐316.8; postvaccine mean [povm] 249.1, SD 257.2, 95% confidence interval [CI] 100.6‐397.6, P = .02) and the single dose dexamethasone (n = 14, prvm 93.14, SD 72.2, CI 51.45‐134.8; povm 185.1, SD 118, CI 116.7‐253.6, P = .01), but not after multiple doses of dexamethasone (n = 14, prvm 194.3, SD 258.3, CI 45.16‐343.4; povm 240.0, SD 235.7, CI 103.9‐376.1, P > .05).ConclusionThe effect of dexamethasone on the postvaccine antibody response varies depending on the dosing frequency and the antigen‐specific antibody type.