Study on the Protective Efficacy of the Japanese Encephalitis Live Attenuated Vaccine SA14-14-2 Against Newly Isolated Genotype I Japanese Encephalitis Viruses

Japanese encephalitis virus (JEV) comprises a single serotype but can be classified into five genotypes (genotypes I–V, GI–GV) based on nucleic acid sequences. Historically, genotype III (GIII) was the predominant strain. However, since the 21st century, genotype I (GI) rapidly replaced GIII as the major genotype in China, Southeast Asia, and other regions. The live attenuated vaccine (LAV) SA14-14-2, licensed in China in 1988, was successfully exported to 13 countries, with cumulative vaccinations exceeding one billion doses. The vaccine seed virus SA14-14-2 belonged to genotype III. Whether this GIII-based vaccine provided sufficient protection against the currently circulating GI strains warranted systematic investigation. In this study, recent JEV isolates collected from China were subjected to genotypic analysis, followed by comprehensive evaluations including protective efficacy against challenge and serum neutralizing antibody levels. The results indicated that, despite antigenic differences between GIII and GI strains, no significant differences in protective efficacy post-challenge were observed. The SA14-14-2 LAV remained effective in preventing GI strain infection.