No cases of polio have been detected so far in the Gaza Strip, the World Health Organisation said on Friday after the virus was found in sewage samples.Sewage now flows between the tents used by tens of thousands of displaced people across the besieged Palestinian territory.On Tuesday, the Global Polio Laboratory Network isolated vaccine-derived poliovirus type 2 in six environmental surveillance samples collected on June 23, WHO spokesman Christian Lindmeier said.The Israeli health ministry said it had made similar findings.“This finding is extremely concerning,” said Lindmeier, “and was sadly anticipated as the entire population of Gaza has been deprived of important public health interventions aimed at preventing and controlling the spread of diseases for over nine months” since the Gaza war began.“The virus has been isolated from the environment only at this time,” Lindmeier stressed, adding there had been “no polio cases detected so far”.Most often spread through sewage and contaminated water, poliovirus is highly infectious and can cause deformities and paralysis.The Gaza war began with the October first week storming of Israel by Palestinian Hamas fighters. Israel’s military retaliation has killed at least 38,848 people, also mostly civilians, according to data from the health ministry in Hamas-ruled Gaza.The WHO, other United Nations agencies and the health ministry in the Hamas-run territory are working to conduct a risk assessment to decide the scope of poliovirus spread, Lindmeier said.They will determine the responses necessary to stop any further spread, including prompt vaccination campaigns, he added. “A timely response is critical,” the spokesman said.“The constraints to implement this response in the current operational context are monumental, and it is entirely within the occupying power’s ability to facilitate before the impact spills over beyond Gaza.“Currently, the risk of international spread of polio cannot be ruled out.” Lindmeier said that polio vaccination coverage was “optimal” in Gaza before the war, at an estimated 89 percent in 2023.Currently only 16 out of 36 hospitals in Gaza are partially functional, with around 45 of the 105 primary healthcare facilities operational.