BREAD Working Paper No. 558, March 2019

Brazil’s Missing Infants: Zika risk changes reproductive behavior

Marcos A. Rengel, Jenna Nobles, Amar Hamoudi


Zika virus epidemics have potential large-scale population effects. Controlled studies of mice and non-human primates indicate Zika effects on fertility, raising concerns about mis- carriage in human populations. In regions of Brazil, Zika risk peaked months before residents learned about the epidemic. This spatio-temporal variation supports differentiation between Zika biological effects on fertility and learning about its risks over 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 peaked, but 10 months after pub- lic health messages advocated childbearing delay in the most affected areas. The evidence is not consistent with biological reductions in fertility being the main force; it indicates strategic changes in reproductive behavior to temporally align childbearing with reduced risk to infant health within locations where Zika risk was more salient to the population. The effects are larger for the more educated, older and wealthier mothers, which may reflect their facilitated access both to information and family planning services within the high-risk/mosquito-infested urban locations.

Keywords: Zika, fecundity, fertility, avoidance, tempo effects

JEL Codes: J13, O15, I15, I18, I12

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