(NEXSTAR) – The U.S. has its first case of polio in nearly a decade after health officials in New York confirmed Thursday that an unvaccinated young adult had contracted the disease. The patient, a resident of Rockland County, had not traveled outside of the U.S.

They developed paralysis, one of the more serious but less common side effects of polio. It appears the patient had a vaccine-derived strain of the virus, perhaps from someone who got live vaccine—available in other countries, but not the U.S.—and spread it, officials said.

The person is no longer deemed contagious. Nevertheless, investigators are trying to figure out how the infection occurred and whether other people were exposed to the virus. “We want shots in the arms of those who need it,” Rockland County Health Commissioner Dr. Patricia Schnabel Ruppert said at a Thursday news conference.

Most Americans are vaccinated against polio, but this should serve as a wake-up call to the unvaccinated, said Jennifer Nuzzo, a Brown University pandemic researcher. “This isn’t normal. We don’t want to see this,” she said. “If you’re vaccinated, it’s not something you need to worry about. But if you haven’t gotten your kids vaccinated, it’s really important that you make sure they’re up to date.”

While there now exists a vaccine that protects 99 out of 100 children who receive it, Americans once lived in fear of the disease, which was responsible for thousands of cases of paralysis each year. Polio can be transmitted through contaminated water, contact with the feces of an infected person, or—less commonly—droplets from a sneeze or cough of someone who has polio. Most of those outbreak-driven cases were in children.

In the vast majority of patients there are either no symptoms or mild effects, but for a smaller proportion of patients—less than 1 in 100—the disease can infect a person’s spinal cord, causing paralysis and possibly permanent disability and death. Children who fully recover may still develop muscle pain, weakness, or paralysis as adults, dozens of years later.

The National Museum of American History’s Behring Center called polio “the most notorious disease of the 20th Century until AIDS appeared.” Since it can be transmitted without symptoms, communities struggled to understand how or why people, most often children, got polio. Before vaccines became available in 1955, isolation was prescribed after confirmed cases in children.

“The enforced separation of families during the early, acute phase of the disease contributed to the intense dread and fear that polio aroused,” according to the center’s website. “Children and parents were not allowed any contact for ten to fourteen days and then only limited visiting for weeks afterward.”

There are two types of polio vaccines. The U.S. and many other countries use shots made with an inactivated version of the virus. But some countries where polio has been more of a recent threat use a weakened live virus that is given to children as drops in the mouth. In rare instances, the weakened virus can mutate into a form capable of sparking new outbreaks.

The Associated Press contributed to this report.