Variant type 2 poliovirus (VDPV) has been isolated from six environmental (sewage) samples in the Gaza Strip, according to the WHO.
The strains – collected from two different collection sites in the southern city of Khan Younis as well as Deir al Balah, further north – are genetically linked to each other, said the WHO-hosted Global Polio Eradication Initiative (GPEI), which added that it was important to note “no associated paralytic cases have been detected”.
However, the agency considers there to be a high risk of spread of this strain within Gaza – and internationally – particularly given the impact of the current situation with public health services.
The oral polio vaccine (OPV) that has brought the wild poliovirus to the brink of eradication provides better immunity in the gut, which is where polio replicates. But the vaccine virus is also excreted in the stool. And in communities with low-quality sanitation, this means it can be spread from person to person and actually help protect the community.
However, in communities with low immunisation rates, as the virus spreads from one unvaccinated child to another over the course of 12-18 months, it also can mutate and take on a form that can cause paralysis, just like the wild poliovirus.
This mutated poliovirus can then spread among under-vaccinated children in the same communities – as cases of vaccine-derived poliovirus (VDPV).
Routine immunisation rates in the occupied Palestinian territory, including Gaza and the West Bank, were estimated at 99% before the start of the conflict on 7 October 2023.
By the end of 2023, vaccination rates had declined sharply to 89%, according to the latest WHO-Unicef routine immunisation estimates. But the data do not separately address Gaza, which has suffered widespread destruction of its health infrastructure.
Inside Gaza, only 16 out of 36 hospitals are partially functional and 45 out of 105 primary healthcare facilities are operational, contributing to reduced immunisation rates. In addition, garbage has piled up, drinking water sources have been damaged or destroyed by the war, and sewage water is pervasive across the enclave in the wake of the breakdown in the sewage treatment plant.
This is in addition to pervasive malnutrition and under-nutrition – increasing infectious diseases of all kinds, including but not limited, to polio.
WHO article – WHO Raises Alarm Over Polio Virus Detected in Gaza Sewage Water Samples (Open access)
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