World Health Organization

is cautioning that possible Zika vaccines are 18 months away from large-scale trials.

GENEVA — Possible Zika vaccines are at least 18 months away from largescale trials, the World Health Organization said Friday as it advised pregnant women to consider delaying travel to areas where the mosquito-borne virus has turned up amid concerns it may be linked to abnormally small heads in newborns.

Meanwhile, Hawaii Gov. David Ige declared a state of emergency to fight Zika virus and another mosquito-borne illness, dengue fever.

The state has been in the midst of a dengue fever outbreak on Hawaii’s Big Island, where there were over 250 confirmed cases.

There have been no locally transmitted cases of the Zika virus in Hawaii, Ige said at a news conference Friday. But there’s concern that the islands could be at risk because mosquitoes that can carry dengue fever also can carry Zika.

Marie-Paule Kieny, the WHO’s assistant directorgeneral for health systems and innovation, said the U.N. health agency’s response is “proceeding very quickly” and that 15 companies or groups are possible participants in the hunt for vaccines.

“(But) our knowledge of what is currently in the pipeline tells us that it will take approximately 18 months before a vaccine can be launched into large-scale trial to demonstrate efficacy,” Kieny said.

Concerns have grown in recent months about a Zika outbreak that has affected at least 33 countries. In Brazil, the epicenter of the outbreak, the spike in cases has coincided with a mysterious rise in cases of microcephaly, or abnormally small heads, in newborns.

The WHO thinks the link between the virus and microcephaly is “more and more probable,” Kieny said but added it will take “weeks to a few months” to determine whether a link exists.

ANTONIO LACERDA/EPA Leticia de Araujo’s 1-month-old daughter was born with microcephaly, after being exposed to the Zika virus during her mother’s pregnancy, in Rio de Janeiro.