Delays in getting children vaccinated during the COVID-19 pandemic and antivaccination sentiment in general may be fueling the most serious threat of polio in the U.S. in years, raising alarms from New York to California.

In the last few weeks, health officials in New York identified the first person in nearly a decade in the U.S. to be diagnosed with polio. The person suffered paralysis. Since then, the polio virus has been found in wastewater not only in two counties in the area where the patient lives but also, as of Friday, in New York City.

The virus may be rebounding worldwide. The Jerusalem area this year suffered an outbreak, and the virus showed up in London wastewater in June.

Now, health experts and officials in California are voicing concern.