An emergency designation from the W.H.O. can prompt action and funding from governments and nonprofits around the world. It elevates the agency to the position of global coordinator and gives its decisions the force of international law. It could also help standardize surveillance of new cases across countries — something that Dr. David L. Heymann, professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine, who chaired the emergency committee, said was critical to getting control over the virus.

The global health agency is trying to strike a balance between alerting the public and scaring it. Zika symptoms are mild or even nonexistent in most people. Overreaction could have the effect of punishing countries that are experiencing epidemics, experts say, for example, through restrictions on travel, trade or tourism that could hurt economies.

The thrust of Monday’s meeting — which was held by teleconference and included presentations from officials of the affected countries — was a renewed emphasis on research to determine whether Zika can cause microcephaly. Dr. Heymann said afterward that he could not discuss the evidence that was presented in a confidential meeting. But he underscored that committee members were mostly concerned that the research efforts, unfolding in multiple countries, were not coordinated.

“The research needs to be pulled together instead of different groups doing different things in their own corners,” Dr. Heymann said in a telephone interview. He added that the committee members were “pretty unanimous” in their decision to recommend emergency status.

Dr. Chan said new case control studies on the connection between Zika and microcephaly will start in the next two weeks. “Can you imagine if we do not do all this work now and wait until all the scientific evidence comes out, people will say why didn’t you take action?” said Dr. Chan, who is trying to cast the agency as a global leader to revive its reputation after a faltering response during the Ebola epidemic in West Africa.