Effect of a hepatitis A vaccination campaign during a hepatitis A outbreak in Taiwan, 2015-2017: a modeling study.

Background. Beginning from 2015-2016, unprecedented large outbreaks of acute hepatitis A that predominantly affected men who have sex with men (MSM) reemerged across the continents. We assessed the impact of an early initiated hepatitis A virus (HAV) vaccination campaign that targeted MSM living with human immunodeficiency virus (HIV) during the 2015-2017 hepatitis A outbreak in Taiwan. Methods. First, we ascertained the effectiveness of HAV vaccination for MSM living with HIV using a nested case-control study of 1470 persons living with HIV who were initially HAV-seronegative. We then fitted a model of HAV transmission among MSM, risk-structured by HIV status, to the actual epidemic curve of reported acute hepatitis A cases in Taiwan during 2015-2017. Results. Fifty-five cases of acute hepatitis A were matched to 220 controls. Single-dose and 2-dose HAV vaccination provided protection rates of 96.1% and 97.8% among recipient MSM living with HIV, respectively. Model fitting yielded basic reproductive number estimates of 7.26 (MSM living with HIV) and 3.04 (MSM not living with HIV). In a counterfactual scenario without an HAV vaccination campaign, the outbreak would have involved 7153 hepatitis A cases during 2015-2017 in contrast to the 1352 that were observed. We therefore estimated that the HAV vaccination campaign averted 80.7% (sensitivity analysis, 48.8%-92.7%) of acute hepatitis A cases that would otherwise have occurred by the end of 2017. Conclusions. The early initiated HAV vaccination campaign, which targeted MSM living with HIV, very effectively curtailed the 2015-2017 hepatitis A outbreak in Taiwan.