Dengue Incidence, Seroprevalence, and Expansion Factors from Active Surveillance, Brazil, 2016–2021

Dengue is hyperendemic in Brazil and is underestimated by passive surveillance. To better understand dengue incidence, we conducted epidemiologic analyses among participants, 2-59 years of age, from the placebo arm of a phase 3 dengue vaccine trial. During 2016-2021, a total of 5,947 participants contributed to 22,028 person-years of follow-up. We identified and virologically confirmed dengue (VCD), Zika, and chikungunya infections. We observed VCD and chikungunya incidence heterogeneity by age, geographic location, and study year. Children 2-6 years of age experienced the highest VCD (2.33/100 person-years) and chikungunya (1.02/100 person-years) incidence. VCD peaked in 2019 (n = 148) whereas chikungunya peaked in 2017 (n = 51). VCD incidence rates from active surveillance were generally higher than those reported to the national passive surveillance system; expansion factor range was <1-9.5 by municipality. Active surveillance is critical to better understand and characterize dengue epidemiology.