The WHO is consulting health experts and institutions in a rare emergency meeting to determine whether the outbreak meets conditions of what it calls a “public health emergency of international concern”.
The UN agency warned last week the mosquito-borne virus was “spreading explosively” in Latin America and that it expects to see four million cases this year.
Dozens of cases of the Zika virus have also been registered in North America and Europe, including five in France, among people returning from vacation or business abroad.
The symptoms of the mosquito-borne virus are relatively mild but WHO chief Margaret Chan said last week the agency “strongly suspected” it was linked to a surge in serious brain deformations in newborns known as microcephaly.
Brazil has been hardest hit, with 270 cases confirmed and 3,448 suspected, but the main difficulty is understanding the exact nature of the link.
“We see microcephaly in a deformed baby now and it’s very difficult to establish what happened nine months ago to the mother,” Lindmeier says. “To gather this and to make the most plausible connection is the challenge right now.”
Governments in the region have cautioned people to delay conceiving until the outbreak is brought under control.
The UN agency admitted it responded too slowly to an outbreak of Ebola in West Africa, which has killed 11,000 since late 2013 but was only declared a global health emergency in August 2014.
The WHO says it learned from the experience and that it was keeping close tabs on Zika.
“What the WHO and the world have learned is to be more transparent, more open and then also a bit quicker in response,” Lindmeier says. “The Brazilian authorities have shared their experiences with Zika and their cases microcephaly immediately with our regional office.”
The WHO said a decision on Zika would come Tuesday or Wednesday.