(NEXSTAR) – The United States 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. and 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, but investigators are trying to figure out how the infection occurred and whether other people were exposed to the virus.

An infamous disease

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. Most of those outbreak-driven cases were in children.

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.

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 as adults.

The National Museum of American History’s Behring Center called polio “the most notorious disease of the 20th Century until AIDS appeared.”

Before vaccines became available in 1955, isolation was prescribed after confirmed cases in children. Since polio can be transmitted without symptoms, communities struggled to understand how or why people, most often children, got it.

“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.”

A national vaccination campaign cut the annual number of U.S. cases to less than 100 in the 1960s and fewer than 10 in the 1970s, according to the Centers for Disease Control and Prevention.

In 1979, polio was declared eliminated in the U.S., meaning there was no longer routine spread.

An effective vaccine

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.

U.S. children are still routinely vaccinated against polio with the inactivated vaccine. Federal officials recommend four doses: to be given at 2 months of age; 4 months; at 6 to 18 months; and at age 4 through 6 years. Some states require only three doses.

According to the CDC’s most recent childhood vaccination data, about 93% of 2-year-olds had received at least three doses of polio vaccine.

Thursday’s announcement is now causing concern in the medical community. Jennifer Nuzzo, a Brown University pandemic researcher, says it should act as a wake-up call for people who are unvaccinated.

“This isn’t normal. We don’t want to see this,” Nuzzo 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.”

The Associated Press contributed to this report.