Duration of Seroprotection of the live attenuated SA-14-14-2 Japanese encephalitis vaccine in children in India


 Background: Acute encephalitis syndrome (AES) is a major public health concern in India and the Japanese Encephalitis (JE) Virus is the most common cause of viral encephalitis in Asia affecting children under the age of 15 years. In India, despite the introduction of the JE vaccine (SA-14-14-2) in the immunization programme, JE continues to account for 15–20% of AES cases to date. The present study evaluates the immunogenicity of live attenuated SA-14-14-2 JE vaccine in terms of persistence of the humoral response after two doses.
 Methods: A cross-sectional study was conducted among 266 children belonging to one of the JE endemic regions of Uttar Pradesh, India. Blood samples were taken from children (2–10 years) and grouped according to the duration (in years) after two doses of the vaccine (five groups with a class interval of two years). Informed written consent was obtained from the parents/guardians. All the samples collected were tested for the presence of anti-JEV-specific IgG antibodies by enzyme-linked immunosorbent assay (ELISA) and further confirmed by micro neutralization test (MNT) and immunofluorescence assays.
 Results: Of the 266 samples tested by ELISA for anti-JEV-specific IgG antibodies, 260 (97.74%) were negative and six (2.26%) were equivocal. The geometric mean immune status ratio across the five groups, 0–2 years (n = 59), 2–4 years (n = 73), 4–6 years (n = 65), 6–8 years (n = 48) and 8–10 years (n = 21) post two doses of SA-14-14-2 JE vaccine was 1.143, 1.059, 1.138, 1.075 and 1.130 respectively and the geometric mean titre (GMT) obtained from MNT across the five groups were 10.77, 8.400, 8.453, 9.517 and 9.674 respectively.
 Conclusion: The study showed a decreasing trend of anti-JEV specific IgG antibody titers across the five groups based on the duration following two doses of SA-14-14-2 vaccine. The results emphasize the significance of booster doses of vaccine for children living in endemic areas.