Polio detected in Gaza may have been imported by aid workers
Poliovirus has been detected in Gaza and it may have been brought in by aid workers, experts have suggested.
Six waste water samples tested by the Palestinian health ministry and UNICEF have come back positive for vaccine-derived polio in Khan Younis and Deir al Balah, suggesting hundreds of people may be carrying the virus across the battered enclave.
The strain detected, type 2 vaccine-derived polio, occurs when the live virus in the oral polio vaccine (OPV) mutates and regains its ability to infect.
Like wild polio, vaccine-derived polio infects the unvaccinated, often via contaminated water or direct person-to-person contact, such as through inadequate handwashing.
The vaccine responsible has not been used in Gaza or surrounding regions since 2016, causing experts to suspect it was brought in by someone who had been in Africa where the vaccine has not yet been phased out.
Dr Hamid Jafari, Director of the Global Polio Eradication Programme, WHO Eastern Mediterranean region, told The Telegraph, the vaccine-derived strain identified in Gaza had been used “quite extensively” to tackle outbreaks in recent years in Africa.
“This strain must have been brought in by someone from a country where this vaccine is used,” explained Dr Hamid.
“Most people carry it asymptomatically. Someone might have come in and excreted it, or perhaps a group of people did – we don’t know at this point.
Some experts have suggested that the strain could have been brought in by a foreign aid worker from a country where that vaccine has been used, or perhaps was brought into Israel by a traveller and spread to Gaza.
“We are still investigating the source; there could be any number of scenarios, but it can’t have originated locally because they don’t use the type 2 oral vaccine,” Dr Jafari said.
The oral polio vaccine is riskier than the inactivated polio vaccine (IPV) because it contains a weakened live virus, which can mutate and infect unvaccinated people.
This risk increases if the weakened virus circulates in a community with low vaccination rates for a long time, giving it a chance to change and become dangerous again.
However, the live vaccine is cheaper, easier to administer, and more effective at stopping person-to-person transmission, making it a top candidate in many low-income countries.
Others have transitioned to a more genetically stable and less risky oral polio vaccination but older versions are still used occasionally.
Polio could ‘thrive’ in Gaza
The fact that polio has been found in Gaza is particularly worrying. Vaccination rates for the disease have fallen from 99 to 89 per cent since the conflict broke out in October last year, leaving thousands vulnerable to contracting the disease.
Overcrowding in densely populated camps and poor sanitation also make transmission far more likely.
“We are incredibly concerned because the conditions in Gaza will allow polio to thrive,” said Dr Jafari.
Although no cases of paralysis – occurring in roughly 1 in 200 infections – have been recorded, this could be due to a lack of surveillance following the collapse of Gaza’s health system, Dr Jafari said.
“The conflict, breakdown of health services, and limited sewage disposal in the area all increase the risk of transmission, as well as the fact that vaccination rates have fallen,” added Dr Kathleen O’Reilly, an epidemiologist and polio expert at the London School of Hygiene and Tropical Medicine.
Note: this story has been updated to emphasise that the source of the polio virus found in Gaza is still being investigated.
Protect yourself and your family by learning more about Global Health Security
