Assessment of Peste des Petits Ruminants Vaccine Effectiveness Under Field Conditions in North East Nigeria

This study empirically assesses the field effectiveness of the PPR vaccine (Nigeria 75/1 strain) against Peste des Petits Ruminants (PPR) in small ruminant populations in North East Nigeria, encompassing Borno, Yobe, Adamawa, Gombe, Bauchi, and Taraba States. PPR is a highly contagious morbilliviral disease causing severe morbidity and mortality in sheep and goats across West Africa, and the Nigeria 75/1 vaccine is the nationally recommended immunising agent. However, vaccine effectiveness under field conditions, including real-world cold chain limitations, administration technique variability, and herd immunity context, has not been systematically evaluated in the North East zone. Using a prospective cohort study design, 400 vaccinated and 200 unvaccinated small ruminants on 40 farms across the six states were serologically monitored by competitive ELISA at 28 days, three months, and six months post-vaccination for protective antibody titres. Seroconversion rates and titre decay kinetics were compared across age groups, sexes, and cold chain categories. Field PPR cases occurring during the follow-up period were recorded. The study provides the first field effectiveness dataset for PPR vaccination in the North East zone. Findings revealed seroconversion in 82 percent of vaccinated animals at day 28, declining to 64 percent by six months. Animals from farms with documented cold chain failure showed significantly lower seroconversion (58%). Field PPR incidence in unvaccinated animals was 3.1 times that of properly vaccinated animals. Keywords: PPR vaccine, field effectiveness, North East Nigeria, seroconversion, cold chain.