Recent studies have predicted that Zika's aggressive spread will diminish within three years as human immune systems adapt to the infection. But new research published in the journal Nature Microbiology shows there could be another 90 million infections - at least - before the current epidemic fades. In Latin America alone, that means at least 1.6 million women of child- bearing age are vulnerable to catching the infection. And Rio de Janeiro is one of the highest- risk cities in the continent, the study reveals.