Reconstructing dengue transmission and assessing future outbreak risk in America Samoa, 2008–2023

Abstract American Samoa experienced multiple dengue outbreaks during 2008–2023. We employed a catalytic model to reconstruct historical dengue virus (DENV) transmission dynamics by estimating the annual force of infection (FOI) – or probability of DENV infection among susceptible individuals – during this period. We incorporated data from 661 dengue cases between 2016–2023 and two serosurveys. We also modeled the proportion of the population with 0, 1, or ≥2 previous infections to assess population risk. We estimated elevated FOIs during 2009 (11%; 95% CrI: 2%–38%), 2010 (15%; 95% CrI: 5%–29%), 2017 (50%; 95% CrI: 37%–67%), and 2018 (13%; 95% CrI 7%–24%). The proportion of the population with 0 previous infections was 22% in 2016, declined to 11% following the 2017–2018 outbreak, and rebounded to 20% in 2023. Our findings indicate a pattern of episodic dengue transmission in American Samoa, with substantial fluctuations in population immunity over time.