Brazil's Missing Infants: Zika Risk Changes Reproductive Behavior

Zika virus epidemics have potential large-scale population effects. Controlled studies of mice and non-human primates indicate Zika effects on fecundity, raising concerns about miscarriage in human populations. In regions of Brazil, Zika risk peaked months before residents learned about the epidemic. This spatio-temporal variation supports differentiation between the biological effects of Zika infection on fertility and the effects of learning about Zika risk on reproductive behavior. Causal inference techniques used with vital statistics indicate that the epidemic caused 20% reductions in birth cohort size 18 months after Zika infection risk peaked, but 10 months after public health messages advocated childbearing delay. The evidence is not consistent with biological reductions in fecundity; it indicates strategic changes in reproductive behavior to temporally align childbearing with reduced risk to infant health. The effects are larger for the more educated, older and wealthier women, which may reflect facilitated access to information and family planning services within high-risk/mosquito-infested urban locations.