Health authorities in New York’s Rockland County say they have seen the pace of their emergency polio vaccination effort stall in recent weeks, amid fierce opposition from anti-vaccine groups. The first U.S. polio case in over a decade was confirmed in the county in July, in a young man who wasn’t vaccinated, and health officials said the illness left him paralyzed.

The slowing immunization campaign comes as states around the country say they are preparing to expand the testing of wastewater to search for undetected cases. Authorities are concerned polio could now be spreading undetected more widely around the country, especially in communities with low vaccination rates.

“We have a lot of infiltration of especially our insular community in Rockland by the anti-vaxxers, and we are now working to supersede them as best we can. It’s going to be very, very difficult,” Rockland County’s chief medical officer Patricia Schnabel Ruppert said last week at a meeting of the federal National Vaccine Advisory Committee.

Schnabel Ruppert said authorities have faced a deluge of nightly robocalls and death threats, aimed at curtailing efforts by staff and leaders in the county’s religious communities supporting the polio vaccination effort. Vaccination rates are especially low in local ultra-Orthodox Jewish communities.

With help from state and federal health agencies, county residents have been blanketed with pleas for polio vaccinations through the outreach and letters. The county is also stepping up “school and daycare audits” in search of unvaccinated children, Schnabel Ruppert added.

“It’s unfortunate that we haven’t sustained that level of increased immunization in the areas that we need. We have a lot more work to do,” she said.

Samantha Fuld, a spokesperson for New York state’s health department, said 11,328 doses of vaccine have been administered to children across Rockland County and neighboring Orange County through September 22.

“The work to vaccinate unvaccinated and under-vaccinated New Yorkers, particularly in the affected communities, is ongoing and will continue,” Fuld said in a statement.

Searching for undetected cases

Only a single confirmed U.S. case has been identified in the outbreak so far. However, the Centers for Disease Control and Prevention has confirmed evidence that the virus is continuing to spread across several counties in New York. 

Many of the positive samples collected from sewer systems, except for those collected from New York City’s Coney Island neighborhood, have been genetically linked to the virus in Rockland County. That case also shares genetic ties to virus samples collected abroad in the United Kingdom and Israel. 

Concerns over undetected cases have spurred the CDC to begin working with health departments to expand their National Wastewater Surveillance System — currently used to help track monkeypox and COVID-19 — to search for polio as well. 

New Jersey’s health department said it has already been working with the CDC to test wastewater for polio. Samples collected through August from a handful of sites have tested negative so far.

The health departments for California, Colorado, Chicago, Los Angeles, Michigan, Minnesota, and Ohio said they are also in talks with federal health authorities about potentially expanding their wastewater surveillance, pending guidance from the CDC.

“It is somewhat complicated for polio as the oral polio vaccine which is given abroad will lead to excretion in wastewater of the vaccine-derived virus,” said a spokesperson for the Los Angeles County Department of Public Health. 

Since 2000, the U.S. has only given shots of what’s called inactivated polio vaccine. However, some vaccine efforts abroad rely on oral polio vaccine (OPV) doses.

“Many visitors to LA may have recently received OPV vaccine in other countries. This would be detected in wastewater. We would need adequate coverage and a baseline to better understand what is happening,” the spokesperson said.

A handful of state health departments – Indiana, Missouri, Pennsylvania and Texas – told CBS News they were not planning to launch polio wastewater surveillance efforts with the CDC.

“The considerations for selection of areas include local vaccination coverage, the extent of travel to and from countries where poliovirus is still circulating, and NWSS presence,” a CDC spokesperson said in a statement.

Polio vaccination rates

Outside of statewide National Immunization Survey data published by the CDC, the Biden administration has released scant official figures on where polio vaccination rates are lowest. The agency last published local estimates back in 2011.

Most states do have some more granular local figures on vaccinations based on data collected from public school districts, which screen for the shots when enrolling kindergarteners.

Another window into polio vaccination comes from data collected by health insurance companies. 

For communities where enough data is available through 2019, new figures shared by the Blue Cross Blue Shield Association suggests some of the nation’s lowest vaccination rates may be in these metropolitan areas:

1. Colorado Springs, CO 73.5%
2. Oxnard-Thousand Oaks-Ventura, CA 78.0%
3. El Paso, TX 78.6%
4. Madison, WI 81.9%
5. Fresno, CA 82.1%
6. McAllen-Edinburg-Mission, TX 82.2%
7. Jackson, MS 82.4%
8. Seattle-Tacoma-Bellevue, WA 83.0%
9. New York-Newark-Jersey City, NY-NJ-PA 83.3%
10. Stockton-Lodi, CA 85.7%

These figures differ from the federal estimates shared by the National Immunization Survey with states. A spokesperson for the Texas Department of State Health Services said 2019’s data for El Paso County puts the polio vaccination estimate at 91.50%.

“It’s concerning that before the pandemic some communities didn’t have enough vaccinated children to reach herd immunity of polio — a disease once eradicated in the United States,” Dr. Adam Myers, the insurer’s chief clinical transformation officer, said in a statement.

The insurer last published a report in 2018 on childhood vaccination levels, including for polio, blaming missed well-child visits with doctors as “a primary driver of under-vaccinated children.”

“The pandemic has likely only exacerbated this and now the U.S. has seen its first polio case in decades,” said Myers.