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Assessment of effectiveness of Japanese encephalitis vaccination in West Bengal, India using sample positivity rate as an alternate measure

1 Integrated Disease Surveillance Programme, State Surveillance Unit, West Bengal; National Institute of Cholera and Enteric Disease (NICED), Indian Council of Medical Research (ICMR), Kolkata, India
2 Integrated Disease Surveillance Programme, State Surveillance Unit, West Bengal, India
3 Directorate of Health Service, Public Health Branch, Government of West Bengal, India
4 All India Institute of Hygiene and Public Health, Kolkata, West Bengal, India
5 National Centre for Disease Informatics and Research (NCDIR), Indian Council of Medical Research (ICMR), Bengaluru, India
6 National Institute of Cholera and Enteric Disease (NICED), Indian Council of Medical Research (ICMR), Kolkata, India

Correspondence Address:
Falguni Debnath,
Scientist C, Division of Epidemiology, ICMR-National Institute of Cholera and Enteric Diseases, P-33, CIT Rd, Scheme XM, Beliaghata, Kolkata 700010
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-9062.321751

Background & objectives: Japanese encephalitis (JE), is a vaccine preventable mosquito borne arboviral disease. The State Health Department of West Bengal, India started a vaccination programme using live attenuated, single dose JE vaccine (SA-14-14-2) in children aged 1- below15 years since 2006 in five districts. The objectives were to compare Sample Positivity Rates (SPR) of Acute Encephalitis Syndrome (AES) cases for JE between vaccinated & unvaccinated districts and observe trend of SPR & Cumulative Incidence in vaccinated districts for three years. Methods: The study was based on the analysis of surveillance data from all tested AES cases including confirmed JE (IgM ELISA) from all JE testing facilities existent in the state during the study period (2011-13). Calculation of Cumulative Incidence, Odds Ratio (OR) with 95% CI, Preventive Fraction and Chi Square for trend (for SPR) was done. Trend of incidence was assessed by linear regression. Results: In three years, 5 vaccinated districts contributed 945 AES and 88 JE cases (SPR - 9.3%) compared to 1807 and 254 (SPR - 14.1%) JE cases in 14 unvaccinated districts. Effectiveness of vaccination was evident by gradual decline of Odds Ratio in favour of vaccinated districts. Vaccination effectiveness of 68% overall and 80% [OR = 0.20 (0.10 - 0.41)] in below 15 years were observed. Trend of SPR was found significantly declining in most of the vaccinated districts. Interpretation & conclusion: Significant reduction in sample positivity rate over three years in most of the vaccinated districts indicated that the vaccination programme had been gradually effective.

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