A mother held her 4-month-old son, who was born with microcephaly, in Olinda, Brazil, on Thursday. Credit Nacho Doce/Reuters

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 on Friday.Scientists are close to confirming those links, Dr. Marie-Paule Kieny, the W.H.O. 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 attempt either to use a molecular technique to detect the virus’s 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.