Urgency Amidst Conflict: Gaza’s Massive Polio Vaccination Campaign After First Case in 25 Years

A massive vaccination campaign is underway in Gaza. The campaign comes amid an armed conflict that has led to the destruction of most of the healthcare and public health infrastructure in the Palestinian enclave. The urgency in doing the campaign came from the discovery of a single case of paralytic polio in a child. . Sewer samples also showed the existence of poliovirus in the territory.

Worldwide, two of the three types of poliovirus have been eradicated. That is, they are nowhere to be found in the world, with only type 1 poliovirus found in the wild (aka “wildtype”). However, there are cases of polio from “vaccine derived” strains. .

When a population is not well-vaccinated, as is often the case in war-torn regions, poliovirus from oral polio vaccine (OPV) . This is because the OPV uses an attenuated virus. These attenuated viruses are still infectious, but they’ve been grown to be less likely to cause disease. “Less likely” is not “unable,” so there are cases of polio from those strains from time to time.

Most people infected with polio do not develop symptoms. , “paralysis (can't move parts of the body) or weakness in the arms, legs, or both—occurs in about 1 out of 200 people to 1 in 2000 people, depending on virus type.” This is why a well-vaccinated population resists cases of even vaccine-derived polio: there are not enough susceptible (non-immunized) people for the virus to infect and make ill.

For example, if 1 in 200 people infected have paralytic symptoms, it would take 200 infected people to have just one bad case. If everyone is immunized, then the probability of 200 people infected is low, and the probability of that one paralytic case is even lower.

In places where polio has been completely eliminated, the (IPV) is used over OPV to prevent polio cases. The reason for this is the very low risk of polio in those regions compared to developing nations and conflict zones. According to the World Health Organization, IPV is used for 2 reasons:

1. “To reduce risks. Once OPV type 2 is withdrawn globally, if no IPV is used, there will be an unprecedented accumulation of children susceptible to type 2 poliovirus. IPV use will help maintain immunity to type 2. This will help prevent emergence of type 2 viruses should they be introduced after the type 2 component is removed from OPV. Thus, a region immunized with IPV would have a lower risk of reemergence or reintroduction of wild or vaccine-derived type 2 poliovirus.”
2. “To interrupt transmission in the case of outbreaks. Should monovalent OPV type 2 (mOPV type 2) be needed to control an outbreak, the immunity levels needed to stop transmission will be easier to reach with use of mOPV type 2 in an IPVvaccinated population compared to use of mOPV type 2 in a completely unvaccinated population. Thus, introducing IPV now could facilitate future outbreak control.”

The good news is that only one of the three known poliovirus types is left: Type 1. Since global efforts to eradicate polio started in 1988, . In 2023, fewer cases were found in these countries compared to 2022. Yet, the virus was detected in more places within these countries through surveillance in wastewater and among people with symptoms. In 2023, eight new countries reported cases of polio caused by the vaccine, as is the case in Gaza now.

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