Assessment of Population Immunity Against Peste des Petits Ruminants in Goats and Sheep in India After the Second...

This study evaluated population immunity against peste des petits ruminants (PPR) in sheep and goats in India following the second annual round of mass vaccination conducted under the National PPR Eradication Programme (PPR EP), launched in 2023 in accordance with the national strategic plan. A cross-sectional post-vaccination evaluation (PVE) was conducted during August 2024 and April 2026 to assess the herd or population immunity under field conditions, in line with the WOAH and FAO Global Control and Eradication Strategy (GCES) of the PPR Global Eradication Programme (PPR GEP) 2030. A total of 52,133 serum samples were collected within 90 days post vaccination from sheep and goats across three age groups, 6-12 months (n = 18,002), 1-2 years (n = 17,316), and >2 years (n = 16,842), representing 1666 epidemiological units across multiple taluks and districts in 20 Indian states and Union Territories. Serum samples were tested for antibodies against PPR virus using in-house IVRI developed hemagglutinin (H) protein monoclonal antibody based competitive ELISA. The study revealed an overall population immunity of 72%, with age-wise PPRV antibody prevalence of 70.8%, 71.8%, and 72.6% in the 6-12-month, 1-2-year, and >2-year age groups, respectively. Statistical analysis showed significant associations (p < 0.005) between PPRV seropositivity and host factors, including species. Population immunity increased markedly from 41% (pre-vaccination sero-prevalence) in 2023 to nearly 72% by 2025-26 following two consecutive rounds of annual vaccination, accompanied by a substantial reduction in confirmed outbreaks from 57 during 2023 to 20 in 2025 in these 20 states/Union Territories. Notably, about 14.5% of epidemiological units remained below 30% seroprevalence, indicating targeted gaps requiring intensified vaccination. Overall animal vaccination coverage exceeded 95% among small ruminants aged above four months, approaching the population immunity threshold of 70 to 80%. These findings highlight the critical role of sustained successive mass vaccination campaigns in achieving and maintaining protective herd/population immunity, thereby supporting national and global PPR eradication goals.