When I went to Nigeria in April 2017 to research a story on the efforts there to stamp out polio, I couldn’t help but be grateful – and a bit mystified – that the disease had been absent so long from Papua New Guinea. With only a small proportion of the country having access to proper toilets and clean water, and collapsing low vaccination rates, PNG appeared vulnerable to this wily and opportunistic virus. And then, this year, polio returned after an 18 year absence. During my research trip in September, I filed this report for The Lancet’s World Report section on the campaign to stop the spread. The story is available free, though you may be required to register an email address to get access: Link is here.