Chien YW, et al. - During the ending phase of a severe dengue epidemic in southern Taiwan, researchers examined adult residents in three administrative districts with high dengue incidence in this cross-sectional seroprevalence study evaluating the true incidence of dengue virus (DENV) infection and the level of herd immunity. They compared the seroprevalence of anti-DENV IgM with the incidence of reported dengue cases in 2015 and realized that 1 out of 3.7 dengue infections was reported to the surveillance system. This high reporting rate may be due to the widespread use of rapid diagnostic tests. In addition, the results indicate a low overall herd immunity and that for vaccination in Taiwan, the current approved Dengvaxia is not quite suitable.