For younger generations on edge after they thought they had figured out how to fend off one virus, the threat of more — like polio and monkeypox — has caught many off guard. Polio may be seared into the memories of many older Americans as a disease with devastating consequences like paralysis and death, but a successful vaccination campaign beginning in the 1950s largely eradicated polio in the United States, and with it, the virus retreated from the public consciousness.

“Polio was once so feared here in the United States, but there’s a reason we don’t fear it anymore, and that’s because of vaccines,” said Dr. William Moss, director of the International Vaccine Access Center at Johns Hopkins University. “This is one of the challenges of vaccines — you prevent a disease and it goes away, and people kind of forget about the disease or why it went away.”…

Dr. Moss said adults who received vaccines decades ago should not be concerned that their vaccine is wearing off. The C.D.C. is considering whether or not to recommend a booster shot to high-risk individuals, Dr. Moss said, but for the time being, that applies only to people who come into regular contact with polio patients either in the United States or abroad.

“In general, people should not worry,” he said. “People who have been fully vaccinated or received at least three doses of a polio vaccine are in general going to be protected and should not worry.”