Protective Efficacy of Vaccines Against Grass Carp Hemorrhagic Disease: A Systematic Review and Meta-Analysis.

Grass carp hemorrhagic disease, mainly caused by grass carp reovirus (GCRV), is a major threat to grass carp aquaculture, and vaccination is considered a sustainable strategy for disease prevention and control. However, the protective efficacy of GCRV vaccines and the factors influencing it have not been systematically synthesised. In this study, literature on GCRV vaccines was retrieved from CNKI, ScienceDirect, and Web of Science in accordance with the PRISMA 2020 statement, covering database inception to March 10, 2026, followed by meta-analysis. After screening, 44 studies were included, of which 24 entered the main meta-analysis. Compared with controls, GCRV vaccines significantly reduced post-challenge mortality in grass carp (RR = 0.473, 95% CI: 0.418-0.536), with substantial between-study heterogeneity (Q = 204.61, p < 0.001; I2 = 88.8%). Subgroup analyses showed that protective efficacy varied by publication period, immunisation route, vaccine platform, and GCRV genotype background. Sensitivity analyses and leave-one-out analyses indicated overall stable results, while publication bias tests suggested possible small-study effects. Descriptive evidence mapping showed a marked increase in GCRV vaccine studies in recent years, mainly focusing on DNA vaccines and subunit/peptide vaccines, with evidence concentrated on GCRV-II. Overall, GCRV vaccines can reduce post-challenge mortality in grass carp to a certain extent, but their protective efficacy is influenced by multiple factors. Future studies should improve antigen matching, standardise evaluation systems, and develop vaccines with both efficacy and field applicability.