There is no end of trouble for the beleaguered people of Gaza. There is widespread destruction, with many buildings and homes damaged or destroyed; the essential infrastructure has been virtually annihilated; a substantial portion of the population has been displaced and is facing the challenges of finding safe shelter and access to basic needs; and now the specter of polio has once again cast a shadow over Gaza. The confirmation of a polio case in a 10-month-old child in Gaza, the first in over 25 years, has set off alarm bells and mobilized the World Health Organization (WHO) and other agencies to initiate a massive vaccination campaign.
The primary question is, what is the origin of this resurgence of polio in Gaza when it was believed that the vaccine had eradicated it? Polio vaccine coverage rates in Gaza were at about 99 percent in 2022 but as a result of the war, they have dropped dramatically. At the same time, the majority of Gaza’s 2.2 million people are now refugees living in shelters with unsanitary conditions, where a lack of clean water and sanitation infrastructure contribute to the spread of disease.
Of the three naturally occurring “wild-type” viruses, only Type 1 remains; Type 2 and Type 3 have been eradicated. However, there is another form to worry about: the so-called vaccine-derived poliovirus. This form now accounts for most outbreaks worldwide.
The outbreak is believed to be linked to a mutated strain of the virus derived from the oral polio vaccine. This strain can spread in communities with low vaccination rates, leading to paralysis in unvaccinated individuals, as tragically occurred with the young child in Gaza whose leg is paralyzed. The situation is exacerbated by the ongoing war between Israel and Hamas, which has disrupted essential services and vaccination efforts, leaving hundreds of thousands of children vulnerable to this preventable disease.
Since 2000, the US and most wealthy countries have used an injected vaccine that does not contain live virus. However, this is not the case in low-income countries which still rely on oral vaccines that contain live, though weakened poliovirus, designed to provoke an immune response that will confer immunity without endangering the health of the recipient. But the weakened virus will likely be shed in stool or bodily fluids, getting into common water systems. That virus may not be as harmful as wild-type poliovirus — at first, but in populations with a low vaccination rate, a vaccine-derived poliovirus may spread in an uncontrolled fashion and eventually revert to a type able to cause paralysis and outbreaks.
This seems to be the situation in Gaza, the pathogen at the root of the outbreak is believed to be vaccine-derived Type 2 poliovirus, according to the W.H.O. Type 2 was removed from the widely used oral vaccines a few years ago, and so many children in Gaza may now be vulnerable.
The planned response is ambitious: vaccinating 640,000 children in just three days with 1.3 million doses of the vaccine. The oral vaccines on the way to Gaza target Type 2 poliovirus, according to the W.H.O., and the campaign will involve 708 teams and 2,700 health workers.
This rapid response is crucial to prevent the further spread of the virus and protect the health of Gaza’s youngest residents. It’s a race against time, as the detection of the virus in sewage samples indicates it may be circulating more widely than initially thought and the fear is that it may emerge in other countries as well.
