Another pandemic hits and it's not well-managed. Everyone, exhausted and resources depleted from COVID-19, don't respond to the new threat or refuse to see it. Nobody has the political capital to call for more lockdowns or rush another vaccine.

It could well be something like Ebola, with a r0 of 1.8, and a high fatality rate. A lot of people will decide that they'd rather risk death to a disease over certain death from poverty.