People living in areas where the Zika virus is circulating should consider delaying pregnancy to avoid having babies with birth defects, the World Health Organization has concluded.

The advice affects millions of couples in 46 countries across Latin America and the Caribbean where Zika transmission is ongoing or expected. At the moment, Puerto Rico is the only part of the United States known to have local transmission of the virus.

Governments of five countries have issued similar advice, as has the health secretary of Puerto Rico, but the Centers for Disease Control and Prevention has decided against this approach on the grounds that government doctors should not intrude on personal decisionsbest made by women and their partners.

W.H.O. Advises Delaying Pregnancy in Areas With Zika Transmissionzika

The W.H.O.’s new guidelines, however, effectively acknowledge that with no vaccine available and mosquito eradication efforts failing to slow transmission of the virus, delaying pregnancy may be the best way that women in affected areas can avoid having children with severe brain damage.

The W.H.O. says men and women of reproductive age “should be correctly informed and oriented to consider delaying pregnancy.” The guidance was originally issued last week but did not garner wide notice among experts until Thursday, when the W.H.O. issued a clarification, distinguishing between people who visit Zika-affected countries and those who live in them.

“It’s about time,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine.

Dr. Hotez, whose medical school is in Houston, where the Zika virus is expected to arrive this summer, has urged women in all Zika-affected areas to consider delaying pregnancy this year. “What happens when Zika hits Texas and the Gulf Coast this summer?” he asked.

The Zika virus, carried by the yellow fever mosquito, has been linked to abnormally small heads and brain damage in infants born to infected mothers, and to neurological damage in infected adults.