LONDON — Scientists are “weeks, not years” from developing a test for the fast-spreading Zika virus, but large-scale clinical trials for a potential vaccine are at least 18 months away, the World Health Organization announced Friday.
The WHO declared Zika a global public health emergency on Feb. 1, only the fourth time it had raised such an alert. The Zika virus — a mosquito-transmitted infection related to dengue, yellow fever and West Nile virus — has spread through Latin America. It was first detected in Brazil in May, and as many as 4 million people worldwide could be infected by year’s end, the health organization has said.
The main public health concern is a suspected link between the virus and two neurological disorders: microcephaly, which is associated with unusually small heads and, often, brain damage in infants; and Guillain-Barré syndrome, in which a person’s immune system attacks part of the nervous system, leaving some almost completely paralyzed for weeks.
Scientists are close to confirming those links, Marie-Paule Kieny, the WHO assistant director general for health systems and innovation, said at a news conference in Geneva.
There is no reliable test yet for Zika. Ten companies are poised to provide tests that try either to use a molecular technique to detect the virus’ presence in blood or to confirm Zika infection by measuring the levels of antibodies in a patient who has been exposed to the virus. Another 10 companies are trying to develop tests using similar approaches.
“It is important to point out, however, that none of these tests have been independently validated and none have regulatory approval,” Dr. Kieny said. She added, however, that “we are talking weeks, not years,” for the first commercial and independently validated tests to become available.
There is no vaccine for Zika, although a race to develop one is underway. Dr. Kieny pointed to two particularly promising efforts: one by the National Institute of Allergy and Infectious Diseases, in Bethesda, Md., and the other by Bharat Biotech, a pharmaceutical company in Hyderabad, India.
“In spite of this encouraging landscape, vaccines are at least 18 months away from large-scale trials,” she said.
Most people who contract the Zika virus experience symptoms like fever, rash, joint pain and red eyes, and there is no lasting harm.
But the risk of birth defects is so serious that El Salvador advised women not to get pregnant until 2018. The Centers for Disease Control and Prevention has urged pregnant women to postpone traveling to more than 20 countries in Latin America and the Caribbean, as well as Puerto Rico, until the public health emergency is brought under control.
The WHO on Friday advised pregnant women to consider delaying travel to any areas where the Zika virus is being transmitted. At the same time, the agency said it was “not recommending any travel or trade restrictions related to Zika virus disease.”
Its advice now brings it in line with public health authorities in the United States, England, Canada and other major industrialized nations who have suggested that pregnant women avoid areas where the mosquito-borne virus is circulating.
Acknowledging that there are at least two cases where sexual transmission of the virus was suspected, the WHO also advised women and their partners who have visited Zika-infested areas to practice safe sex “including the correct and consistent use of condoms.”
Although the virus was discovered in the Zika forest of Uganda in 1947, it did not come to prominence outside Africa and Asia until 2007, after an outbreak in the South Pacific.
Dr. Kieny acknowledged that “relatively poor knowledge of the Zika virus” had hampered the response to the outbreak in Latin America.
Recently, she said, scientists reported the case of a European woman who became pregnant while living in Brazil and who had an abortion when it was clear the child would have microcephaly. Tests confirmed the presence of the Zika virus in the fetus’ brain.
“Can you treat a fetus in the womb, in the mother, and try to eliminate the virus?” Dr. Kieny asked. “At which stage can you do it? These are all questions that are not resolved at the moment.”
Dr. Kieny noted that even the relationship between the Zika virus and microcephaly was not yet clear. In Colombia, scientists are monitoring a group of pregnant women who have the virus.
“In a few weeks or months, we will find out how many of these women deliver a child with microcephaly,” she said.
On Friday, Thomas Bach, the president of the International Olympic Committee, said no countries had announced plans to pull out of the Summer Games in Rio de Janeiro over concerns about the virus.
Mr. Bach, speaking before the opening ceremony of the Winter Youth Olympics in Lillehammer, Norway, said on Friday that he had “full confidence” in the steps taken by the Brazilian government and global health organizations.
“We are taking the situation very seriously,” he added.