Also, a microcephaly study launches in Brazil and new mosquito control efforts are being explored.
The WHO said though Zika virus has circulated in Africa before, the effect of an importation from the Americas is unclear.
Also, the CDC shares new guidance on babies and children with acute infections.
Pope Francis's comments coincide with WHO guidance on preventing sexual transmission of the virus.
The finding of the virus in amniotic fluid adds evidence to a possible link between Zika and microcephaly.
The agency says even though the virus has not been confirmed in the US blood supply, the risk is real.
A robust immune response in mice clears the way for tests in nonhuman primates.
The WHO's mosquito-control assessment spoke to the complex and daunting task, but also acknowledged a possible role for newer tools.
Also, Brazil's health ministry rejected a possible microcephaly link to larvicides, and experts are gathering for a US Zika priority workshop tomorrow.
The WHO's top drug and development official projected the launch of a large vaccine trial is still at least 18 months away, but a test might be available within weeks.