The CDC will test sewage for the virus in communities outside of New York

The U.S. will expand polio sewage surveillance to communities with low vaccination rates outside the New York City metro area, where an outbreak over the summer paralyzed an unvaccinated adult and raised questions about how widely the virus spreads.

The Centers for Disease Control and Prevention said in a statement Wednesday that it is working with health officials in Michigan and Philadelphia to identify communities with low vaccination rates and begin testing wastewater in those areas. The CDC said it is in preliminary discussions with other state and local health departments about expanding testing to other parts of the United States.

Federal health officials will expand sewage surveillance for polio to counties in New York that have potential links to communities known to harbor the virus. The CDC said the expanded surveillance program will help determine whether poliovirus is present in other parts of the United States and direct efforts to increase vaccination rates in at-risk communities.

Effluent testing will last at least four months once initiated. The CDC described the expanded surveillance program as strategic and focused only on certain at-risk communities.

The decision by federal health officials to expand polio surveillance comes after an unvaccinated adult in Rockland County, New York, was paralyzed by the virus over the summer. The CDC considers paralysis caused by polio a public health emergency because it is so rare and indicates community-wide spread of the virus.

Public health officials later confirmed that the virus was indeed widespread after sewage samples from five other New York counties tested positive. The Rockland patient had not traveled internationally, meaning they almost certainly picked up the virus from someone else in the community.

The virus circulating in the New York area is related to a strain used in the oral polio vaccine. The U.S. stopped using the vaccine 20 years ago because it uses a live but weakened virus that can mutate and become virulent in rare cases, posing a threat to unvaccinated people.

Other countries still use the oral polio vaccine because it is cheap, effective, easy to administer, and generally safe. The United States uses inactivated polio vaccine as a series of vaccines. It uses a killed virus that cannot be copied or modified.

Although the Rockland County patient is believed to have contracted polio through local transmission, the chain of transmission may have originated abroad from someone who received the oral vaccine.

The CDC said the risk to the general public is low because more than 92% of Americans are vaccinated against polio. The vaccine is very effective in preventing severe disease and paralysis, although it does not stop the virus from spreading.

Oral vaccination is very effective in preventing transmission and is usually used to suppress outbreaks. The CDC is in discussions about introducing a new version of the oral vaccine to address rare outbreaks like New York’s.