After starting its own testing of polio wastewater last year, Canada found two samples of polio vaccine type 2 (VDPV2).
According to the epidemiological update of the World Health Organization (WHO) and the Pan American Health Organization (PAHO) published on December 30, 2022, the virus strain was detected in two wastewater samples collected between August 20 and August 30, 2022.
The report said the sampling sites chosen for testing were in communities connected to New York state, but did not provide exact locations. The report said there were no suspected or confirmed cases of acute flaccid paralysis, the most common syndrome caused by polio, in the areas where Canadian sewage samples were taken.
In August 2022, New York State reported emerging samples of the virus in its wastewater after an unvaccinated patient was diagnosed with polio, marking the first case of polio reported in the US in nearly a decade.
After cases emerged overseas last summer, the Public Health Agency of Canada (PHAC) said it would begin wastewater testing and surveillance for the virus. Canada has not reported a case of polio since 1994. The presence of VDPV2 in the two samples collected in August was confirmed on December 23, 2022.
The Canadian National Microbiology Laboratory, which collected the samples in Canada, did not detect polio in sewage samples collected between October 31 and November 9. However, the lab will continue to test archived samples collected from the target sites in September and December.
The report said WHO/PAHO will work with PHAC to follow up on the findings. CTVNews.ca has also reached out to PHAC for comment, but has yet to hear back.
“PAHO/WHO reiterates to Member States the need to continue efforts to achieve optimal levels of population immunity through high and homogeneous vaccination coverage,” the report said. “(And) through sensitive epidemiological surveillance that allows for the timely detection and investigation of all cases of acute flaccid paralysis (AFP).”
Since September 2022, the U.S. has reported 94 wastewater samples testing positive for polio, 87 of which were linked to the confirmed case in Rockland County, New York, according to the report.
The WHO and the US Centers for Disease Control say VDPV is a rare strain of polio genetically altered from the original, weakened strain contained in the oral polio vaccine.
“If allowed to circulate in under- or unimmunized populations for long enough, or to replicate in an immune-deficient individual, the weakened virus can revert to a form that causes disease and paralysis,” the CDC says on its website, while emphasizing , that the oral polio vaccine is safe and “instrumental in eradicating wild polioviruses worldwide.”
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