Analyzing a hepatitis A outbreak by integrating space-time distances and network approach as evidences-based assessment of vaccination policy

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Purpose: Acute hepatitis A (AHA) is one of notifiable diseases in Taiwan, and a significant decrease in incidence was documented after vaccination to high risk children in 1995. However, a rapid increase in AHA was noted since June 2015 which signaled an outbreak. Hepatitis A Virus (HAV) vaccine has been considered as a main measure for disease prevention. Past researches indicate the effectiveness of vaccine to interrupt an outbreak largely depend on targeting right groups and immunization coverage rate. This study proposes a framework to identify the epidemiological patterns of AHA in order to predict the effectiveness of vaccination on different groups. Methods & Materials: A total of 128 laboratory-confirmed AHA patients reported to Taiwan Centers for Disease Control in 2015 were investigated and information on sexual risk behaviors, history of sexual transmitted diseases (STDs), and HAV viral sequence were collected. We divided the patients into two groups, case group was defined as patients with identical HAV sequence (n=81) and others were control group (n=47). This study identified clustering patterns by local indicators of spatial autocorrelation. Space-time distances and social network analysis (SNA) were integrated to assess potential effects of vaccination under different scenarios by centrality indices. Results: In case group, all were male, 51(63.0%) had been infected with HIV, syphilis or gonorrhea, and 33(40.7%) of the cases performed anilingus during communicability period, whereas none of the controls did. Moreover, the cases compared with the controls demonstrated a spatial cluster pattern (Moran's I: 0.39 and 0.14, respectively). By means of SNA, our finding indicated that vaccination to cases with STDs history would not significantly diminish the efficiency of transmission. Only when provided vaccination to all the people at risk and reached at least 20% coverage rates would abate an epidemic of AHA effectively (2% lower compared with no intervention, p<0.05). Conclusion: This study demonstrates a framework not only to recognize the epidemiological patterns but also as an instrument for assessing vaccination policy in hepatitis A outbreak. These results suggest that the effectiveness of interventions integrated with immunization delivery deserved further investigation.