Concomitant administration of live attenuated Japanese encephalitis chimeric virus vaccine (JE-CV) and measles, mumps, rubella (MMR) vaccine: Randomized study in toddlers in Taiwan

Background: Japanese encephalitis (JE) is the most important cause of viral encephalitis in Asia. Methods: In this randomized, open-label, multicenter trial in 550 children aged 12 to 18 months in Taiwan, children received one dose of JE-CV and one dose of MMR vaccine. Vaccines were either administered separately 6 weeks apart (Groups 'JE-CV' and 'MMR', named after which vaccine was given first), or concomitantly (Group 'Co-Ad'). JE neutralizing antibody titers were assessed using PRNT₅₀. MMR antibody levels were determined by ELISA. Results: All groups had low seroprotection/seropositivity rates (<10%) before vaccination for all antigens. Forty two days after vaccination, on either Study Day 42 or 84, seroconversion rates for all antigens were high in all groups, irrespective of the order of vaccinations. Seroconversion for JE ranged from 96.9% in Group Co-Ad on D42 to 100% in Group MMR. Non-inferiority was demonstrated for all analyses as the lower bound of the 95% CI of the difference in seroconversion rates between groups was above the pre-defined limit of -10.0%. The immune responses remained high for all antigens and well above the level of protection 12 months after vaccination in all groups. There were no safety concerns. Conclusions: JE-CV is safe and induces a strong protective immune response which persists over 1 year when co-administered with MMR vaccine.