<p>The tetravalent dengue vaccine Dengvaxia^® may prime dengue-seronegative vaccinees for antibody-dependent enhancement (ADE) of any subsequent dengue (in case of vaccine failure) or Zika infections. Many researchers associate ADE of such cases with more severe outcomes including death. This study uses a mathematical model of transmission dynamics that distinguishes ADE and non-ADE cases for each virus, to identify the potential impact of a dengue screening and vaccination campaign on the economic cost and disease burden of a dual dengue-Zika outbreak, under the hypothesis that severe outcomes are associated with ADE. Results indicate that when all dengue exposure is to a single serotype, in most cases vaccination increases both cost and burden because they are dominated by the high costs associated with complications from ADE Zika cases. However, if per-case ADE Zika costs are lower than estimated (a real possibility given the limited data available), by a factor ranging from 1 to 6 (for cost, except in Vietnam) or 8 (for burden), sufficiently high vaccination coverage can reduce total cost and burden substantially over a year. Analysis also identifies variations across countries, dengue serotypes, and timeframes of evaluation.</p>