Characterizing the Zika virus antibody response Given the public health emergency that Zika virus poses, scientists are seeking to understand the Zika-specific immune response. Stettler et al. analyzed 119 monoclonal antibodies isolated from four donors that were infected with Zika virus during the present epidemic, including two individuals that had previously been infected with dengue virus, another member of the flavivirus family. Neutralizing antibodies primarily recognized the envelope protein domain III (EDIII) or quaternary epitopes on the intact virus, and an EDIII-targeted antibody protected mice against lethal infection. Some EDI/II-targeting antibodies cross-reacted with dengue virus in vitro and could enhance disease in dengue-infected mice. Whether dengue and Zika virus antibodies cross-react in humans remains to be tested. Science , this issue p. 823