WHO estimates up to 4 mln infected by Zika virus in the Americas

Chile's Health Minister Carmen Castillo holds a flyer that reads "Zika virus recommendations" during an information campaign by the Health Ministry at the departures area of Santiago's international airport, Chile January 28, 2016. [Photo/Agencies]

Experts strongly suspect two main factors have driven the virus' progress in the Americas according to WHO, which also explained that though a causal relationship between Zika virus infection and birth defects including babies being born with abnormally small heads and other neurological syndromes has not been established.

"First, the population is totally naive in terms of immunology against this virus. The second point is that the vector is everywhere in the Americas, from southern United States to northern Argentina," Aldighieri said.

WHO Assistant Director-General Bruce Aylward warned that though the Zika virus is currently circulating at a very high intensity in the region, gaps remain regarding the situation on the ground.

"With respect to China and Asia, at this moment we don't have any official notification of Zika virus in that area," he said, adding he did not know what would be the required timeframe, or indeed the feasibility, of developing a vaccine.