In 13 years as an infectious-disease doctor in the suburbs of New York City, Azfar Chak has fought viruses, both routine and rare. But he had never experienced a summer of viruses like this one. No one had, at least not in this part of the world. A third year of the coronavirus, driven by a more contagious variant. Global outbreaks of monkeypox and a mysterious hepatitis afflicting previously healthy children. Polio virus found in the sewage systems in London and New York. And polio diagnosed in patients in Jerusalem and Rockland County where Chak works, a region of more than 300,000 people just north of New York City. The return of polio, one of the most feared diseases in the early 1950s, was particularly unnerving. In the 800-page medical review Chak read recently to prepare for recertification, he found “almost no mention of polio. Because we were under the impression that it was pretty much eradicated.”