Zika virus infection of first-trimester human placentas: utility of an explant model of replication to evaluate correlates of immune protection ex vivo.

•ZIKV crosses the uterine–placental interface and infects the developing fetus.•ZIKV replicates in explants of human basal decidua and anchoring villi.•Cytotrophoblasts and Hofbauer cells are ZIKV targets in first-trimester placentas.•ZIKV-infected cells proliferate and titers increase ex vivo.•Protective antibodies elicited by ZIKV vaccines can be evaluated in explants.