Abstract The global frequency and complexity of viral outbreaks is increasing. In 2015, Brazil experienced an epidemic caused by the Zika virus. This represents the first known association between a flavivirus and congenital disease, thus marking a `new chapter in the history of medicine' [Brito 2015]. We use administrative records to document household and health personnel responses to the epidemic over two phases: (i) between May and October 2015, when it was known that Zika was in Brazil, but its symptoms were thought to be dengue-like and without consequence for those in utero; (ii) following an official alert on November 11th recognizing the link between Zika and congenital disease. On household behavior, we find a 7% reduction in pregnancies post-alert, a response triggered immediately after the alert, and driven by higher SES women. On responses during pregnancy, there is an increased use of ultrasounds (9%) and abortions (5%), especially late term abortions. These impacts are driven by mothers that conceived post-alert. There is a lack of response during pregnancy among mothers that conceived just pre-alert, despite their unborn children also being at risk. As a result, those conceived pre-alert are significantly more likely to be born with low birth weight, and the rise in microcephaly is concentrated in this cohort. On responses of health personnel, we document an increased administration of dengue tests to pregnant women post-alert (that lacking a formal test for Zika was the best approach to diagnosis), and no change in counseling on contraception for women seeking to become pregnant. Our results provide a rich picture of household and health personnel responses to an evolving epidemic. They suggest disseminating information about Zika is less effective among those already pregnant and at risk, but for those yet to conceive, the primary welfare cost of the epidemic is disease avoidance, as they move away from unconstrained fertility paths, or abort pregnancies.