Following recent reports of the first polio case in the United States in almost a decade, the Centers for Disease Control and Prevention (CDC) reported the virus has been detected in wastewater samples as far back as June. The CDC indicates the polio detections were found in Rockland County, a region north of New York City known for its notoriously low vaccination rates.
On July 21st, New York State Department of Health officials reported a case of polio in a young adult from Rockland County. The individual had developed serious polio paralysis and was unvaccinated.
Upon announcing the case, health officials indicated the infection was linked to a vaccine-derived strain of the virus known to infrequently spread in countries still using an older form of polio vaccine that utilizes an active form of the virus. However, the subject had not traveled internationally recently so the source of infection was unknown.
Now, in a new statement from the CDC, it has been revealed traces of the same vaccine-derived strain of polio found in the previously confirmed case have been detected in wastewater samples taken from Rockland County as far back as early June. The CDC stressed there have been no further cases of polio reported but the long-standing wastewater traces suggest it is possible some community transmission of the virus has been occurring over the past few months.
An accompanying statement from the Global Polio Eradication Initiative (GPEI) reported on the genetic sequencing of the polio strain found in Rockland County, affirming it was vaccine-derived type 2 poliovirus (VDPV2). It was also confirmed that this polio strain in the US can be linked to a previously reported case of polio detected in London in June.
“Following the detection, the Global Polio Laboratory Network (GPLN) has confirmed that the VDPV2 isolated from the case is genetically linked to two Sabin-like type 2 (SL2) isolates, collected from environmental samples in early June in both New York and greater Jerusalem, Israel, as well as to the recently-detected VDPV2 from environmental samples in London, UK,” the GPEI stated. “Further investigations – both genetic and epidemiological – are ongoing to determine possible spread of the virus and potential risk associated with these various isolates detected from different locations around the world.”
While paralytic poliomyelitis is the most notorious outcome from infection with poliovirus it is actually quite rare. Almost three-quarters of polio infections are asymptomatic, and the majority of those who do recognize an infection will only experience mild flu-like illness.
The public health challenge is that polio is very infectious, and can easily spread asymptomatically across multiple people before causing serious paralytic outcomes in less than 1% of infections. This, alongside an incubation period that can stretch for two to three weeks, make polio a difficult disease to contain once it has spread through a community.
New York State health officials are currently calling for all unvaccinated persons in the state to come out and get vaccinated. This includes a particular focus on anyone who is pregnant and infants aged two months or older. According to the CDC, the currently used polio vaccine in the US contains an inactive form of the virus and is 99% percent effective.
Rockland County in particular has been cited as an area of concern due to its low rates of vaccination. Its current polio vaccination rate among two-year-old children is only 60.5%, significantly lower than the New York State average of 79.1%.
"Polio is a dangerous disease with potentially devastating consequences," said New York State Health Commissioner Mary Bassett. "In the United States, we are so fortunate to have available the crucial protection offered through polio vaccination, which has safeguarded our country and New Yorkers for over 60 years. Given how quickly polio can spread, now is the time for every adult, parent, and guardian to get themselves and their children vaccinated as soon as possible."