Antibody responses to Japanese encephalitis virus and dengue virus serotype 2 in children from an orthoflavivirus endemic region after IMOJEV vaccination

Abstract

Background: Japanese encephalitis virus (JEV) is a mosquito-borne pathogen that causes severe neurologic disease. Its endemicity in Asia has prompted its inclusion in nationwide immunization programs. However, the Philippines, which is also endemic for related viruses like dengue (DENV), has not yet adopted this practice. Vaccine hesitancy is a major challenge, exacerbated by concerns over cross-reactive antibodies that may enhance viral infection. This study aimed to determine whether IMOJEV vaccination would induce cross-neutralizing or enhancing antibodies against DENV.

Methodology/principal findings: Pre- and one-month post-vaccination samples from IMOJEV-vaccinated Filipino children (9-24 months old) were analyzed. A reporter virus particle (RVP)-based neutralization assay against JEV showed neutralization in 28/29 subjects post-vaccination. Presence of DENV2-reactive antibodies was measured via DENV2 VLP ELISA, which revealed increased DENV2 binding reactivity post-vaccination. Pre-vaccination DENV2 binding reactivity also had no significant correlation with the JEV vaccine response. RVP-based neutralization and enhancement assays against DENV2 showed that there was no significant change in neutralizing or enhancing antibody activity against DENV2 after JEV vaccination.

Conclusions/significance: This study shows that IMOJEV vaccination elicited a JEV neutralizing response in 97% of vaccinees and that the magnitude of JEV neutralizing titers post-vaccination was not associated with pre-existing binding antibodies to DENV2. Further, while live JEV vaccination increases DENV2-binding antibodies, this cross-reactivity does not lead to DENV2 enhancement. These findings contribute to a better understanding of the orthoflavivirus antibody response following immunization and the influence of pre-existing heterologous orthoflavivirus antibodies. This could guide vaccination strategies, especially in orthoflavivirus-endemic regions.

Fig 1. Baseline IgG binding to DENV2 and JEV VLP.

(A and C) Binding reactivity to (A) DENV2 or (C) JEV of children younger than 12 months versus children 12 months and older prior to vaccination (two-tailed Student’s t-test; broken lines at P/N cut-off; horizontal bars represent the mean). (B and D) Relationship between age and binding reactivity against (B) DENV2 or (D) JEV (two-tailed Spearman rank correlation test). (E) Relationship between DENV2 and JEV binding reactivities (two-tailed Spearman rank correlation test).

Fig 2. Antibody response to IMOJEV vaccination.

(A) Comparison of log₁₀ JEV RVPNT50 titers pre- and post-vaccination (one-tailed paired Student’s t-test; titers less than 10 were assigned a value of 5). (B) Pairwise comparison of JEV VLP IgG binding reactivity pre- and post-vaccination (one-tailed paired Student’s t-test; in red is subject B27, who did not respond to vaccination based on the RVP neutralization assay). (C and D) Comparison of post-vaccination log₁₀ JEV RVPNT50 titers (C) between age groups and (D) by DENV2 reactivity (two-tailed unpaired Student’s t-test).

Fig 3. DENV2 binding reactivity and functional antibody responses.

(A) Pairwise comparison of DENV2 VLP IgG binding reactivity pre- and post-vaccination (one-tailed paired Student’s t-test). (B) Relationship between the fold change in DENV2 and JEV VLP IgG ELISA P/N values after vaccination (one-tailed Spearman rank correlation test). (C and D) Pairwise comparison of DENV2 neutralizing titers or fold enhancement post-JEV immunization (two-tailed paired Student’s t-test; broken lines at cut-off for neutralization or enhancement and shown in red circles is subject B27 who did not respond to JEV vaccination; in Fig 3C, the line at y = 0.7 represents 13 subjects that did not have neutralizing activity pre- and post-vaccination).