Zika keeps spreading, and so does the concern about the virus. Even though it's mild for most of us. It's a big threat to pregnant women and a vaccine isn't imminent.

FOX's Simon Owen in our European bureau has more:

The World Health Organization stepping up warnings in its guidance on avoiding Zika, saying for the first time that pregnant women should consider delaying travel to an affected area, places like parts of Brazil.

The WHO's doctor Marie-Paule Kieny saying progress is being made on a vaccine, but:

(Kieny) "In spite of this encouraging landscape, vaccines are at least 18 months away from large scale trials."

Scientists are also still working to formally confirm or dismiss a strongly-suspected link between Zika, and birth defects.

In London, Simon Owen, FOX News.