Seroprevalence and Placental Transfer of Zika and Dengue Virus Antibodies in Postpartum Women in Southeast Brazil.

Zika (ZIKV) and dengue (DENV) viruses are major public health concerns in Brazil. Understanding population serological status, particularly in pregnant women, is vital for estimating their spread. This study assessed ZIKV and DENV seroprevalence in pregnant women and the transplacental transfer of antibodies to their newborns, crucial for early-life protection. A cross-sectional seroprevalence study was conducted with 601 postpartum women and their newborns in São Paulo city, Brazil post-ZIKV fever outbreak. Paired maternal and umbilical blood samples were collected for ZIKV and DENV antibody testing, which was conducted using ELISA and virus neutralization tests. Maternal and neonatal sociodemographic and clinical data were obtained from interviews and medical records. ZIKV and DENV neutralizing antibodies (nAbs) were detected in 2.4% and 31.6% of participants, respectively. Maternal place of birth, parity, education level, and prenatal Toxoplasmosis serology were identified as risk factors associated with ZIKV and/or DENV infection. Effective transplacental transfer of specific ZIKV and DENV antibodies from mothers to newborns was observed. Nulliparous women and those with a history of DENV infection exhibited higher transfer ratios (TR) of DENV antibodies. Low-birthweight and preterm neonates had lower DENV-1 antibody TRs than heavier and term infants. Low seroprevalence of ZIKV and DENV antibodies in the study population indicates a high vulnerability to infection by these viruses. Maternal and neonatal characteristics were associated with seropositivity for ZIKV and DENV and the efficiency of DENV antibody transfer to neonates. These findings can guide public health strategies for evaluating the TR effectiveness of antibodies following future ZIKV and DENV vaccination programs in pregnant women.