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 occurring or expected. According to a recent study, more than five million babies are born each year in parts of the Western Hemisphere where the mosquitoes known to spread the virus are found.

At the moment, Puerto Rico, the United States Virgin Islands and American Samoa are the only parts of the United States with local transmission of the virus. But clusters of cases are expected to appear in Florida and along the Gulf Coast this summer.

The 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 decisions best made by women and their partners.