Lin KY, et al. - Experts intended to assess the serologic responses and effectiveness of hepatitis A virus (HAV) vaccination in human immunodeficiency virus (HIV)–positive individuals during the outbreak in Taiwan. Anti-HAV immunoglobulin G was prospectively determined among all HIV-positive individuals from June 1, 2015, to September 30, 2016. It was concluded that two-dose HAV vaccination was effective at preventing HAV infection among HIV-positive individuals receiving combination antiretroviral therapy during the outbreak of acute hepatitis A. This investigation highlighted the importance of HAV serologic screening and vaccination to prevent outbreaks of acute hepatitis A in at-risk populations.