Age-Related Immune Responses and Long-Term Immunity in Adult Sheep and Goats Following Vaccination with the Nigeria 75/1 Live Attenuated PPR Vaccine

In 2023, a highly immunogenic live attenuated vaccine based on the Nigeria 75/1 strain was introduced in Kazakhstan to provide protection against PPR. This study presents the results of a three-year animal trial evaluating the vaccine’s efficacy, safety, and immunogenicity. The novelty of this study lies in the long-term (up to 36 months) evaluation of protective immunity in adult animals, as well as in the comparative analysis of immune responses across different age groups and the assessment of viral suppression following challenge infection. Sheep and goats of different age groups were included, including lambs and kids aged 1.5 and 3 months, as well as adult animals aged 2–3 years. The vaccine was well tolerated following a single immunization, and no clinically significant adverse effects were observed in vaccinated animals, apart from only mild transient local reactions. A strong humoral (IgG) response to PPRV antigens was detected in all groups, with the highest antibody titers observed in young animals. Seroconversion was detected in 100% of vaccinated animals by day 21 post-vaccination. Long-term protective immunity (at least 36 months) was demonstrated in adult animals, whereas in young animals early protection was confirmed at 21 days post-vaccination along with subsequent humoral immune dynamics following a single immunization with a 1.0 mL dose of the vaccine (Nigeria 75/1 strain, titer 103.0 TCID50/mL). These findings indicate that the vaccine is well tolerated, highly immunogenic, and provides sustained protection in adult animals while inducing early immune responses in young animals.