Zika virus (ZIKV) and dengue virus (DENV) co-circulate in endemic regions and are genetically and antigenically similar, but whether pre-existing immunity to DENV promotes or supresses ZIKV emergence is unknown. A recent study finds that pre-existing immunity to DENV is associated with a reduction in ZIKV transmission. The authors prospectively followed a cohort of 1,453 individuals living in Salvador, Brazil — the epicentre of the 2015 outbreak in the Americas. By performing multiple serological assays that distinguish between ZIKV and DENV infections on samples collected before and after the outbreak, they found that ~73% of the cohort was infected with ZIKV during the outbreak. In individuals with immunity to DENV before the outbreak and high antibody titres, there was a reduction in the risk of ZIKV infection and symptoms. Together, these findings support the hypothesis that prior DENV infection had a role in driving ZIKV to local extinction by reducing transmission.
Rodriguez-Barraquer, I. et al. Impact of preexisting dengue immunity on Zika virus emergence in a dengue endemic region. Science 363, 607–610 (2019)