Efficacy of avian influenza oil-emulsion vaccines in chickens of various ages.

An experimental avian influenza (AI) oil-emulsion vaccine was formulated with 1 part inactivated A/turkey/Wisconsin/68 (H5N9) AI virus emulsified in 4 parts oil. Broilers were vaccinated subcutaneously (SC) either at 1 or 3 days old or at 4 or 5 wks old. Commercial white leghorn (WL) layers were vaccinated SC at 12 and 20 wks old or at only 20 wks old. Maximum geometric mean hemagglutination-inhibition titers postvaccination (PV) were 1:86-1:320 for broilers, 1:597 for twice-vaccinated layers, and 1:422 for once-vaccinated layers. Ninety to 100% of vaccinated broilers were protected against death and morbidity when challenged with highly pathogenic A/chicken/Penn/83 (H5N2) AI virus 4 weeks PV, and all were protected when challenged 8 wks PV. All controls and most vaccinates were infected by challenge virus, and 90-100% of controls died or exhibited clinical signs. Vaccinated commercial pullets were protected against morbidity, death, and egg-production decline at either peak of lay (25 wks old) or at 55 wks old. All unvaccinated controls became morbid or died, and egg production ceased 72 hours after challenge. The 0.5-ml vaccine dose was determined to contain 251 and 528 mean protective doses (PD50S) in 4-wk-old and 1-year-old SPF WL chickens, respectively, challenged 4 wks PV.