Effectiveness of Japanese encephalitis SA 14-14-2 live attenuated vaccine among Indian children: Retrospective 1:4 matched case-control study

Abstract

Objectives: We estimate the effectiveness of Japanese encephalitis (JE) SA 14-14-2 live-attenuated vaccination single dose campaign among children aged 1-15 years in India during 2006-07.

Methods: Acute encephalitis syndrome (AES) cases hospitalized following vaccination campaigns during the years 2006-08 were investigated retrospectively. The laboratory-confirmed JE cases were detected from the surveillance laboratories based on anti-JE IgM antibody by ELISA or viral RNA detection by RT-PCR in sera or cerebrospinal fluid. Consent was sought from parents or guardians. Four community controls were chosen randomly per case during house-to-house survey employing individual matching on age, gender and residence during the risk period. Vaccination history was enquired from the child's guardian and verified from vaccination card at home or records at health centre. Conditional logistic regression was conducted on matched case-control sets.

Results: We studied 149 cases and matched 596 controls. Vaccination effectiveness was 43.8% (95% CI, 1.9-67.8) based on vaccination card or record. However, effectiveness was 72.2% (95% CI, 56.2-82.4) based on parental history or card/record. Vaccination effectiveness in Assam state was higher than in Uttar Pradesh state.

Conclusions: We concluded that the single subcutaneous dose of SA 14-14-2 JE vaccine provided moderate effectiveness in Indian children.

Keywords: Japanese encephalitis; Live attenuated vaccine; Mass vaccination campaigns; Matched case control study; Vaccination effectiveness; Vaccine-preventable diseases.