Flawed implementation of a global eradication strategy brought poliovirus to Gaza, and wartime conditions let the infection spread.

The first round of an international campaign to vaccinate children in the Gaza Strip against polio ended in mid-September, with nearly 560,000 kids receiving initial doses amid staggered humanitarian pauses in the war there.

Alarm bells sounded in August when a 10-month-old baby boy in the Gaza Strip was partially paralyzed by poliovirus. The case made history as the territory’s first confirmed report of polio in 25 years—and it offered public health organizations grim confirmation that poliovirus detected earlier in wastewater in central and southern Gaza was indeed circulating among the region’s residents.

Independent monitors are now confirming the exact proportion of children who have received a dose of the campaign’s vaccine, but the initial round appears to have met the target required for herd immunity: a minimum of 90 percent of all children 10 years and younger. Relief workers doled out doses amid challenging circumstances, operating in brief, nine-hour windows of peace and against a backdrop of ongoing mass displacement. Stamping out the virus, however, will require a repeat of this performance: children need two doses of this vaccine each for effective protection against polio.

Ideal Conditions for Polio

Driving the urgency of the campaign is the “uniquely horrifying” picture of polio, says Paul A. Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia. The virus primarily affects children under five, and in one out of 200 people, causes lifelong or fatal paralysis. No treatments can reverse such paralysis. Only vaccination prevents the disease. In communities that fail to meet the high threshold for herd immunity, the virus spreads easily and quickly.

Prior to the onset of the war in Gaza, 99 percent of residents were immunized against polio. Israel’s bombardment of the region has since rendered two thirds of its hospitals inoperable and driven almost two million Palestinians from their homes. At the start of September, the vaccine coverage rate rested at a low 86 percent.

It is difficult to estimate the number of Gazans infected with the virus. The majority of people do not show symptoms, and the quarter who do can mistake their fatigue, fever or headache for a cold or the flu. The clearest sign of the disease, paralysis, is rare, which suggests reports of a 10-month-old without the ability to sit up or of three children with suspected polio-induced muscle weakness could be “the tip of a much bigger iceberg,” Offit says.

Unsanitary conditions make exposure to the virus all but certain. In Gaza today, clean water is scarce; sewage gathers into puddles on the streets, and shelters offer one toilet for every 700 residents. As a stomach bug, poliovirus spreads best via contact with feces. And in addition to contaminated surfaces or dirty food and water, the virus also spreads from person to person via sneezing and coughing—a route of transmission that could play a large role in cramped refugee camps.

Those at highest risk for paralysis are children born since the disruption of Gaza’s health care system, says Roland W. Sutter, now retired epidemiologist who was formerly at the Global Polio Eradication Initiative (GPEI). These infants are more likely to have missed out on several or all routine vaccinations, though some may harbor varying levels of protective maternal antibodies against the virus from their time in utero.

It’s vital that the campaign in Gaza succeed not only for the children there but for children in neighboring areas and worldwide. Today polio regularly circulates in just two countries: Afghanistan and Pakistan. But in recent years, even regions long considered to be polio-free have seen a resurgence of the virus because of patchy vaccine coverage. Between 2021 and 2022 Mozambique and Malawi reported a total of nine cases. London also saw a small outbreak in 2022. And the same year a 20-year-old man in Rockland County, New York State, became the U.S.’s first case of paralytic polio in nearly a decade. These outbreaks, Sutter emphasizes, illustrate the hefty challenge polio eradication efforts face. “If we’re not successful everywhere, then children are not safe anywhere,” he says.

Tracing the Path of the Virus

Indeed, the arrival of the particular strain of type 2 poliovirus in Gaza reflects a string of failures to contain the pathogen elsewhere. A related strain was last seen in Egypt and is thought to have crossed the border to Gaza as early as September 2023. The strain in Egypt itself emerged as a by-product of an imperfect outbreak response and is what’s known as a vaccine-derived virus—a pathogen generated when traces of a particular polio vaccine reach large, unprotected populations.

The broadly popular oral poliovirus vaccine, or OPV, uses live, weakened virus, which recipients can shed in their stool. If that weakened virus manages to spread from host to host, it can gradually revert to a dangerous form that is capable of invading the nervous system. Such events are rare: vaccine-associated paralysis emerges from one of every 2.7 million doses. But because wild-type polio cases have fallen dramatically over the past 30 years, vaccine-derived viruses now constitute the main source of illness, sometimes contributing several hundred annual cases.

Few other vaccines use a live, weakened virus, and even those that do so do not spark outbreaks like OPV does. The latter vaccine’s use poses a unique threat and has been controversial for this reason. OPV played a pivotal role in squashing the U.S.’s polio epidemic in the 1960s, for instance, but led to an average of nine cases of paralysis per year throughout 1989 and about six per year throughout the 1990s. In 2000 the U.S. adopted the strict use of inactivated poliovirus vaccine (IPV), a product that is delivered as a shot.

But the oral vaccine has unique advantages that make it attractive in a range of global settings. It’s cheap and easy to manufacture, and whereas health care workers trained in sterile injection procedure dispense IPV, anyone can administer OPV, a dose of which consists of a few drops in the mouth. Moreover, the vaccine elicits a more powerful immune response than IPV, not only preventing disease but stopping the spread of the virus. The same mechanism that allows the vaccine to cause a low number of polio cases also allows communities with few resources to more easily reach herd immunity: children vaccinated with OPV often pass the weakened virus to their family members, thereby immunizing them as well.

Of course, to eradicate polio, GPEI knows it must eventually phase out the use of OPV. So in 2016, in what’s called “the switch,” the initiative attempted a trial run: it swapped global supplies of trivalent OPV—a vaccine that protects recipients against all three types of wild poliovirus—for a bivalent version that mounts immune responses only to types 1 and 3. Type 2 had last been seen in 1999, so researchers believed removing it would eliminate the possibility of further vaccine-derived type 2 cases. Their logic was sound, but global execution of the strategy backfired, says Kimberly M. Thompson, founder of the nonprofit Kid Risk and a disease modeler for GPEI. Vaccine-derived type 2 virus had quietly lurked in several communities, and after the swap, small outbreaks of vaccine-derived cases popped up, which global polio-eradication partners failed to stamp out as planned. As a result, cases of vaccine-derived type 2 polio—such as those in Gaza—have increased more than 10-fold since 2016.

No Easy Fix

In 2020 the World Health Organization authorized emergency use of a new vaccine intended to lower the chances of vaccine-derived type 2 cases: novel oral polio vaccine type 2 (nOPV2). For the novel formulation, researchers tweaked the genetic code of the live, attenuated virus from type 2 OPV to generate a strain that is 80 percent less likely to mutate and become dangerous. Raul Andino-Pavlovsky, a virologist at the University of California, San Francisco who helped design nOPV2, sees the product as a necessary revamp of a decades-old vaccine. It’s what the current vaccination campaign is using in Gaza. But even nOPV2 can revert back to a paralytic form, preventing it from serving as a “magic bullet,” Thompson notes. In fact, the virus spreading in Gaza itself evolved from previous use of nOPV2, a spokesperson for the World Health Organization told Scientific American .

The complex factors that led to this outbreak have renewed debate over how best to eradicate polio. Some epidemiologists suggest reversing the switch and returning to trivalent OPV for routine immunizations. Others say public health systems could combine bivalent OPV and nOPV2, or that GPEI could develop a safer trivalent OPV vaccine in the style of nOPV2. A vocal minority contends that the benefits of OPV use do not outweigh the risks. “It’s unconscionable to use an unsafe product,” Offit argues. “I have to believe that if we brought ourselves together, we could go into communities and inoculate with IPV.” He and others see particular promise in nascent efforts to create microneedle patch products that stick to skin. (IPV must be delivered as a shot because the inactivated virus could not otherwise enter the bloodstream and ward off poliovirus en route to the spine or brain. If taken orally, the inactivated virus would likely be destroyed by the harsh environment of the stomach.)

For now, public health officials in Gaza are focusing on setting up the next round of vaccinations, which are scheduled to take place in late September or early October. Many are optimistic that the campaign will reach its 90 percent target—that is, so long as peace holds during planned pauses in the war. Failure to attain high vaccination coverage, however, could not only allow the current strain to spread further throughout Gaza and to adjacent countries but also potentially seed new vaccine-derived strains. GPEI therefore plans to carefully monitor wastewater concentrations of the virus and polio cases in the Eastern Mediterranean region in the coming months.

Halting the spread of the virus would represent a real triumph for the children of Gaza, as well as for the initiative. If the campaign succeeds, polio eradication partners will have worked at “unprecedented scale and speed,” said Richard Peeperkorn, the WHO’s representative for the occupied Palestinian territory, in a recent press release . Yet as long as the war persists, Gazans will continue to struggle to access necessary health care. Children in particular are at risk for a host of vaccine-preventable illnesses, including measles, cholera and pneumonia. Many are also expected to lose their lives to starvation and bombing.

“Gazans have a lot more to worry about than just polio,” Andino-Pavlovsky says.

AWFSM CATEGORIES
Activism | AI | Belief | Big Pharma | Conspiracy | Cult | Culture | Deep State | Economy | Education | Entertainment | Environment | Faith | Global | Government | Health | Hi Tech | Leadership | Politics | Prophecy | Science | Security | Social Climate | Universe | War