Immune Response At 12-23 Months Following A Single Dose Of Vero Cell Culture-Derived Japanese Encephalitis (Je) Vaccine In Adults Previously Vaccinated With Mouse Brain-Derived Je Vaccine

Background: Japanese encephalitis (JE) virus is an important cause of neurological disease in Asia. JE vaccine is recommended for travelers with higher JE risk itineraries. Inactivated Vero cell culture-derived JE vaccine (JE-VC) is the only JE vaccine currently available in the United States. An inactivated mouse brain derived JE vaccine (JE-MB) previously was available but production was discontinued. One JE-VC dose administered to adults previously vaccinated with >= 3 doses of JE-MB provides good short-term protection for at least one month, but data on longer-term protection are limited. We evaluated non-inferiority of the JE virus neutralizing antibody response at 12-23 months in JE-MB-vaccinated adults administered one JE-VC dose compared with JE vaccine-naive adults administered a JE-VC two-dose primary series.Methods: We obtained archived sera from U.S. military personnel and performed a 50% plaque reduction neutralization test for anti-JE virus neutralizing antibodies. We compared the geometric mean titer (GMT) and seroprotection rate at 12-23 months after one JE-VC dose in previously JE-MB-vaccinated personnel and after the second JE-VC dose in previously JE vaccine-naive personnel. Non-inferiority was concluded if the lower bound of the two-sided 95% confidence interval (CI) of the GMT ratio in previously vaccinated to vaccine-naive personnel was >1/1.5.Results: The GMT in previously JE-MB-vaccinated persons was 75 (95% CI 63-90) and in previously JE vaccine-naive persons was 12 (95% CI 11-14), and seroprotection rates were 94% (235/250) and 54% (135/250), respectively. The ratio of GMTs was 6.3 (95% CI: 5.0-7.7), satisfying the criterion for non inferiority.Conclusions: One JE-VC dose in previously JE-MB-vaccinated military personnel provides good protection for at least 1-2 years. The benefits of administration of a single JE-VC dose in previously JE-MBvaccinated adults include a shorter time to completion of re-vaccination before travel, a decrease in the risk of adverse events, and reduced costs.