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A field study on Nakayama and Beijing strains of Japanese encephalitis vaccines
S Nimmannitya1, S Hutamai, S Kalayanarooj
1Children's Hospital, Bangkok, Thailand.
Insights
A three-dose Japanese encephalitis (JE) vaccine schedule, with the third dose given 6 months after the second, provides optimal protection for children. This approach ensures higher, longer-lasting immunity against JE virus infection compared to a two-dose regimen.
Area of Science:
- Pediatric Infectious Diseases
- Immunology
- Vaccinology
Background:
- Japanese encephalitis virus (JEV) poses a significant threat to children's health.
- Evaluating the immunogenicity of different JE vaccine strains is crucial for effective public health strategies.
- Thailand has a low incidence of JEV infection, making it a suitable location for vaccine efficacy studies.
Purpose of the Study:
- To compare the immune responses of children aged 1-6 years to Nakayama and Beijing strains of JE vaccines.
- To determine the optimal timing and dosage for JE vaccine administration to ensure sustained immunity.
- To assess the seroconversion rates and susceptibility to JEV infection following different vaccination schedules.
Main Methods:
- A field study was conducted in Mae Hong Son Province, Thailand.
- Children received either Nakayama or Beijing strain JE vaccines in a 3-dose schedule (doses 1 & 2 one to two weeks apart, dose 3 one year later).
- Seroconversion rates and geometric mean titers (GMT) were measured at various time points post-vaccination.
Main Results:
- Both vaccine strains induced high seroconversion rates (approximately 94%) after two doses.
- Seroconversion rates declined to 10-20% (or 50-65% with cross-protection) 6-12 months after the second dose, indicating susceptibility.
- A third dose of either vaccine strain boosted seroconversion to 100%.
Conclusions:
- A 3-dose JE vaccination schedule is recommended to reduce susceptibility and provide longer protection.
- Administering the third dose at 6 months after the second dose is suggested for optimal immune response.
- Both Nakayama and Beijing JE vaccine strains are effective for use in Thailand.
Abstract:
A field study to compare the immune response of children aged 1-6 years to Nakayama and Beijing strains JE vaccines was carried out in Mae Hong Son Province, northwest Thailand, where there was low incidence of JEV infection. The first and second dose of each vaccine was given 1-2 weeks apart and the third dose was 1 year after the second dose. Seroconversion rate was similarly high, about 94% in both groups of vaccinees. At 6 and 12 months after 2 doses of vaccines, the seroconversion rates dropped in both groups of vaccinees, so there were 10-20% of children (50-65% if cross protection was considered) susceptible to JEV infections during this period. After the third dose of vaccine, the seroconversion rate rose to 100% in both groups. The GMT in Bejing strain vaccinees were slightly higher than Nakayama strain JE vaccines. To reduce the number of susceptible children during 6-12 months after the second dose and for longer protection, the primary JE immunization should be 3 doses and the timing for the third dose should be at 6 months after the second dose. Either Nakayama or Beijing strain vaccine could be used in Thailand.