After initiating its own wastewater polio tests last year, Canada detected two samples of vaccine-derived polio virus 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 found in two wastewater samples collected between December 20 and August 30, 2022.
The report said the sampling sites chosen for the test were in communities connected to New York state, but did not provide exact locations. The report says there have been no suspected or confirmed cases of acute flaccid paralysis, which is the most common syndrome caused by polio, in the areas where the Canadian sewage samples were taken.
In August 2022, New York State reported samples of the virus appearing in its wastewater after an unvaccinated patient was diagnosed with polio, marking the first time a polio case has been reported in the US. USA after almost a decade.
After the emergence of cases abroad last summer, the Public Health Agency of Canada (PHAC) said it would begin testing wastewater 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, found no polio in wastewater samples collected between October 31 and November 9. However, the laboratory will continue to analyze archived samples collected from selected sites in September and December.
The report said that 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 receive a response.
“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 states. “(And) through sensitive epidemiological surveillance that allows timely detection and investigation of all cases of acute flaccid paralysis (AFP).”
Since September 2022, the US has reported 94 wastewater samples that tested positive for polio, of which 87 are linked to the confirmed case in Rockland County, New York, according to the report.
The WHO and the US Centers for Disease Control say that VDPV is a rare strain of poliovirus, genetically modified from the weakened original strain contained in the oral polio vaccine.
“If allowed to circulate in underimmunized or nonimmunized populations long enough, or to replicate in an immunocompromised 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 has been “instrumental in the eradication of wild polioviruses around the world.”
