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, marking a ‘new chapter in the history of medicine’ [Brito 2015]. We use tens of millions of administrative records to document household responses to a public health alert linking the emerging Zika virus and congenital disease. 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, we find an increased use of ultrasounds (9%) and abortions (5%), especially late term abortions. However, these impacts are driven by mothers that conceived post-alert – there is no response to the public health alert during pregnancy among mothers that conceived just pre-alert, despite their unborn children also being at risk. The primary welfare cost of the epidemic is disease avoidance, as households move away from planned fertility paths. We conclude by discussing the extent to which our findings extend to household responses to public health alerts on other emerging viral threats.