First Polio Case in Nearly a Decade Is Detected in New York State

However, a regional health assessment reported that in 2016 about half of children in Rockland County had received all of their routine childhood vaccinations by 35 months of age, one of the lowest rates in the region. To achieve herd immunity for polio, the target vaccination rate is 80 percent, according to the World Health Organization.

Disruptions caused by the Covid-19 pandemic depressed vaccination rates for routine immunizations for children around the globe and in the United States, according to some studies. Misinformation and mistrust related to Covid vaccines have also affected childhood vaccination rates, as more parents have expressed fears about long-established vaccines.

Dr. Amesh A. Adalja, senior scholar at Johns Hopkins Center for Health Security, said that vaccine hesitancy could give vaccine-derived polio strains “an opportunity to cause damage” in a community that has large pockets of unvaccinated people.

Polio is very contagious, the Health Department said in a news release. People can spread the disease even if they do not have symptoms, which can include fatigue, fever, headache, muscle pain and vomiting. Rarely, polio cases may result in paralysis or death.

The oral vaccine is safe and effective and is still given in countries where vaccine access is more limited. However, people who receive the oral vaccine, which contains a weakened version of the virus, may shed the virus.

The shedding feature was initially thought of as an advantage, Dr. Adalja said.

“It mimics natural infection, and people shed the virus, the vaccine virus, and that spreads to other people, and then they get immunized that way,” he said. “One of the negative aspects is that, in very rare cases, that vaccine strain can lead to paralysis in someone” who is not vaccinated, he said.

The United States uses an injected polio vaccine that contains inactivated virus instead of live virus.

Jesse McKinley contributed reporting.