Zika may have already infected more than 1 million people. Most have recovered, and an estimated 80 percent do not experience symptoms. The WHO’s declaration on Zika was intended to jump-start scientific research, vaccine and treatment development, and mosquito-control campaigns.

WHO officials blamed the slow Ebola response on budget cuts that hit programs on infectious disease control — as well as on poor communication between Ebola-affected countries and WHO headquarters in Geneva. Despite ongoing budget pressures, in 2016 the WHO said that the need for greater scientific knowledge on Zika drove its public health emergency announcement. And surely the WHO, after being accused of dragging its feet with Ebola, wanted to act quickly with Zika.

Political scientists would argue that the story is still more complicated. In “Rules for the World,” Michael Barnett and Martha Finnemore show that international organizations’ internal workings and technical expertise influence their actions in ways that are sometimes at odds with the goals of the countries that set up these organizations to work on their behalf.

» The WHO has six autonomous regional offices that behave differently.