Maternal immunity and post-vaccination sero-monitoring in small ruminants for peste des petits ruminants eradication in North Shewa, Ethiopia

Abstract

Ethiopia aims to eradicate peste des petits ruminants (PPR) by 2027 through a risk-based vaccination strategy (RBVS); however, outbreaks continue to occur. This cross-sectional study (January–May 2024) evaluated RBVS performance by assessing flock- and maternal-level antibody immunity, providing field-based evidence to inform PPR control and eradication efforts. A total of 594 serum samples were collected using simple random sampling to assess flock (n = 508) and maternal (n = 86) antibody immunity. All samples were tested for PPRV antibodies using a competitive enzyme-linked immunosorbent assay (c-ELISA). Overall individual animal-level antibody immunity was 65.35% (332/508), while at the flock level only 22.27% of flocks (6/22) had ≥ 80% of animals with detectable antibodies. Multivariable logistic regression showed significant differences in immune status by age group (p < 0.05). Adult (284/428, 66.36%) and older (26/33, 78.79%) small ruminants were approximately three and four times more likely to be seropositive than young animals (52.21%), respectively. Significant district-level variation was also observed: animals in Basona-werena (116/146, 79.45%) were three times more likely to be seropositive than those in Menz-mama (88/155, 56.77%). Overall maternal antibody immunity in kids and lambs was 52.3%, with 61.29% (95% CI: 42.19–78.15) in kids and 47.27% (95% CI: 33.65–61.20) in lambs. This study demonstrates insufficient maternal and flock-level antibody immunity against PPRV in vaccinated small ruminants, with levels below the recommended 80% threshold. To improve coverage, vaccination efforts should prioritize young animals, districts with low antibody levels, and areas with poor past performance. Strengthening surveillance, refining vaccination strategies, enhancing sero-monitoring, and ensuring efficient vaccine distribution are essential for effective PPR control and eventual eradication.