The Zika epidemic could be over in three years – but by then up to 93.4 million people may have been infected, including 1.65 million women of childbearing age, and tens of thousands of babies could be affected. But even if the epidemic fizzles out, this could be a temporary relief: a decade later, the virus may well be back.

Zika arrived in the Americas from Asia in 2013. Since then it has spread rapidly, as people in the region had no previous exposure or immunity to the virus. The babies of women infected early in pregnancy have been born withmicrocephaly and other birth defects; a recent World Health Organization estimate suggests there have been 1781 brain-damaged babies born in countries recently infected with the virus.

Meanwhile, two people in Florida are expected to be confirmed as the first to catch the virus from mosquitoes in the US. Surveillance is so sparse that the virus could already be spreading widely, undetected, in the southern US, says Peter Hotez at Baylor College of Medicine in Houston, Texas.

Novel infections spread unhindered only until so many people have been exposed and become immune that the virus is unlikely to encounter people who are still susceptible. Not everyone needs to be immune for this “herd immunity” to happen and the epidemic to burn out.

You can read more on New Scientist.