Polio Is Exploiting a Very Human Weakness

In 1988, the World Health Assembly announced a very ambitious goal: Polio was to be vanquished by the year 2000. It was a reach, sure, but feasible. Although highly infectious, polioviruses affect only people, and don’t hide out in wild animals; with two extraordinarily effective vaccines in regular use, they should be possible to snuff out. Thanks to a global inoculation campaign, infections had, for years, been going down, down, down.

But 2000 came and went, as did a second deadline, in 2005, and a third, in 2012, and so on. The world will almost certainly miss an upcoming target at the end of 2023 too. In theory, eradication is still in sight: The virus remains endemic in just two countries—Pakistan and Afghanistan—and two of the three types of wild poliovirus that once troubled humanity are gone. And yet, polio cases are creeping up in several countries that had eliminated them, including the United Kingdom, Israel, and the United States. Earlier this year, New York detected America’s first paralytic polio case in nearly a decade; last week, the governor declared a state of emergency over a fast-ballooning outbreak.

This is the cruel logic of viruses: Give them enough time—leave enough hosts for them to infect—and they will eventually find a way to spread again.