# Unveiling immunity dynamics: Serological characteristics of antibodies against Japanese encephalitis virus in Guangdong, China

## TL;DR

This study examines antibody levels against Japanese encephalitis virus in Guangdong, China, revealing high seroprevalence and the need for improved vaccination strategies.

## Contribution

The study provides new insights into immune dynamics and vaccination effectiveness against Japanese encephalitis in a specific Chinese population.

## Key findings

- High seroprevalence of anti-JEV antibodies was observed, indicating ongoing transmission.
- Antibody positivity rates showed a U-shaped age distribution, with the lowest in adolescents.
- Two doses of live attenuated vaccine were associated with higher antibody titers than one dose.

## Abstract

Defining the immune dynamics of Japanese encephalitis (JE) in healthy individuals is crucial for assessing population susceptibility and evaluating the effectiveness of vaccinations.

We conducted a cross-sectional serological survey of anti-JEV IgG antibodies and anti-JEV neutralizing antibodies (nAbs) in Guangzhou City, Zhanjiang City and Heyuan City of Guangdong Province, China.

A total of 691 participants were included from 2018–2022, among whom 50 were dengue IgG antibody positive and 641 were dengue IgG antibody negative. In the total population, the anti-JEV IgG antibody positivity rate detected by enzyme-linked immunosorbent assay (ELISA) was 51.37% (95% CI: 47.64–55.11%), and the neutralizing antibody positivity rate detected using the microneutralization test (MNT) was 73.22% (95% CI: 69.92–76.54%). Among the 641 dengue IgG antibody-negative subjects, the anti-JEV IgG antibody positivity rate by ELISA and the neutralizing antibody positivity rate by MNT were 48.05% (95% CI: 44.17–51.93%) and 72.07% (95% CI: 68.59–74.56%), respectively. Comparable geographical seroprevalences of either anti-JEV IgG or neutralizing antibody were observed in Guangzhou City, Heyuan City and Zhanjiang City, respectively (49.52% vs. 48.04% vs. 47.45%, 65.71% vs. 70.46% vs. 76.47%, respectively). Antibody positivity rates in all age groups exhibited a U-shaped curve, with the lowest rate occurring in the 7–18-year-old age group. With respect to the vaccine dose, the anti-JEV nAb positivity rate and geometric mean titer (GMT) detected by MNT were higher in those who received two doses of live attenuated vaccine than in those who received one dose or 0 doses (80.57% vs. 55.81% vs. 55.09% and 25.92 vs. 12.19 vs. 16.47, respectively). In the 641 dengue IgG antibody-negative subjects, moderate consistency between the MNT and ELISA results was observed (Kappa = 0.47, rs = 0.76).

The high seroprevalence in participants indicated a neglected transmission of JE, which highlights the importance of strengthening the surveillance of JEV in this area. The vaccination program against JEV is highly needed because of immune gaps in adults, e.g., boosters for adults aged 7–39 years.

Japanese encephalitis (JE) is an acute central nervous system disease caused by Japanese encephalitis virus (JEV) and is primarily prevalent in Southeast Asia and the Western Pacific. Vaccination is the most effective preventive measure. Although vaccination has significantly reduced the incidence of JE in children, the proportion of adult cases has been gradually increasing, highlighting the need for ongoing immune monitoring and strategic adjustments. In this study, we measured the levels of anti-JEV IgG antibodies and anti-JEV neutralizing antibodies (nAbs) in the serum of healthy participants in Guangdong Province, China, as well as their trends of change and correlations with vaccination. The seroprevalence distribution in Guangdong Province revealed a low seroprevalence among adolescents and a high seroprevalence among adults, indicating the potential for JEV transmission in the region. These findings indicate the need for enhanced JEV surveillance and adjustments to the vaccination program, particularly booster vaccinations for the 7–39-year-old age group. Overall, the findings of this study provide guidance for adjusting the Japanese encephalitis vaccination strategy.