Researchers are warning that at least 2.6 billion people in the world may be at risk of being infected with the Zika virus. 

A study published in The Lancet Infectious Diseases says there are about 1.2 billion people in India living within the geographical range for the Zika virus. China has 240 million people at risk and Indonesia has just under 200 million.

A key risk area identified is Angola in southwestern Africa, due to its strong cultural ties and travel links with Brazil.