12 Deadly Diseases Cured in the 20th Century

How A Vaccination Campaign Aims To End Polio In Gaza

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.

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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.

The Taliban Suspends Polio Vaccine Campaign In Afghanistan – Here's The Likely Impact

The Taliban recently announced that they are suspending its polio vaccination campaign in Afghanistan. The announcement was made shortly before the campaign was due to start.

The suspension is temporary, according to the Taliban, and is due to security fears and the fact that women are involved in administering the vaccine.

Poliovirus is a highly infectious virus that mainly affects children under the age of five, but anyone who is unvaccinated can be infected. The virus spreads from person to person mainly through traces of contaminated faeces on people's hands getting into their mouths or, less commonly, through contaminated food or water.

It initially infects the intestines, leading to symptoms such as fever, fatigue, headache and vomiting in the early stages of the disease. But, as the infection progresses, the virus can invade the nervous system, often leading to paralysis. In the worst cases, affected children will die as the paralysis spreads to the muscles that control breathing.

Polio was a major global childhood health concern in the 19th and 20th centuries. However, the development of polio vaccines has given us the ability to prevent polio-induced paralysis. There are two main types of polio vaccine: live-attenuated oral poliovirus vaccine (OPV), made from weakened poliovirus, and inactivated poliovirus vaccine (IPV).

Following the introduction of the Global Polio Eradication Initiative in 1988, OPV and IPV have nearly eliminated the disease. Yet polio remains a global threat, as was seen recently with the emergence of polio in the Gaza Strip.

Afghanistan is one of only two countries, alongside neighbouring Pakistan, where polio has continued to spread. So the news that the Taliban have suspended polio vaccination will probably have major consequences for the control of the disease in Afghanistan and the surrounding region.

Earlier in 2024, Afghanistan had used a house-to-house vaccination strategy, recommended by the WHO, for the first time in five years. This tactic ensures that most children have access to the vaccine. However, in the southern Kandahar province, the Taliban used a mosque-to-mosque vaccination campaign, which has been proven to be less effective. So Kandahar is believed to have a large number of unvaccinated children who are now susceptible to infection.

House-to-house vaccination was used in early 2024. Muhammad Sadiq/EPA

Locally, this setback in vaccination not only poses a risk to the children of Afghanistan, but also poses a risk to children in bordering Pakistan. This is due to the high levels of movement across the borders between the two countries.

"Afghanistan is the only neighbour from where Afghan people in large numbers come to Pakistan and then go back," Anwarul Haq, the coordinator at the National Emergency Operation Centre for Polio Eradication, told Associated Press.

Afghanistan has already seen an increase in paralytic polio cases in 2024, rising from six in 2023 to 14 confirmed cases in 2024 so far. Paralysis occurs in about one in 200 infections, so this increase in paralytic polio suggests a much wider spread of infection in the region. This includes Pakistan, which has reported 13 cases so far this year.

With the reduced number of vaccinations and an increasing number of children vulnerable to polio infection, we are likely to see an increased number of paralytic polio cases in the near future. This potential increase in viral spread coupled with the number of people travelling in and out of the region may lead to the spread of polio beyond Afghanistan and Pakistan and into areas such as India and Iran.

Unfortunately, those who are not vaccinated will also be susceptible to vaccine-derived poliovirus. This is where the OPV vaccine, which contains a weakened version of the virus, has been able to spread in areas with low vaccination coverage, allowing the virus to return to virulence.

This has seen new vaccine-derived outbreaks seeded across several countries in Africa, Asia and the Middle East, which now accounts for most paralytic polio cases worldwide.

Why Polio Is Making A Comeback

This commentary was adapted from episode 142 of the Health & Veritas podcast.

Polio is back in the news, again.

Over two years ago, we talked about a serious polio threat in the New York area, when one person developed paralytic poliomyelitis and wastewater detected the virus in several adjoining and nearby counties. Less than 1% of all infections result in paralytic polio; when we see wastewater evidence of polio, we know people are being infected, but generally only when we see clinical poliomyelitis do we get to know precisely who was infected. That outbreak extinguished itself without more harm.

Throughout the world, we have continued to see vaccine-derived polio outbreaks, including the recent outbreak in Gaza (listen to my Tik Tok for more about that). That's one of the main reasons why richer nations, including our own, have shifted to inactivated polio vaccines. But these vaccines can only be very effective at extremely high uptake rates and when polio is nearly eradicated already.

Listen to episode 45 of the Health & Veritas podcast to understand more of the nuance, but in brief the oral polio vaccine is the vaccine-of-choice for the Global Polio Eradication Initiative (GPEI) because it 1) provides superior mucosal immunity against subsequent infection and spread of wild polio virus, 2) spreads from vaccinees to close contacts (and thus immunizes some individuals not reached by immunization programs), 3) can be rapidly administered by volunteers in the form of oral drops (which is important during large vaccination campaigns), and 4) is relatively affordable compared to inactivated poliovirus (by an order of more than 10:1).

But today, I am not talking about a vaccine-derived polio outbreak. For the first time in several years, we have a worsening outbreak of wild-type polio, in Pakistan. Wild type polio—the original polio—has been on the cusp of eradication except for one major region in the world, Pakistan and Afghanistan. There has been enormous progress, with fewer than two dozen cases for several years running. But that progress is being partially undone now. In Islamabad, the capital of Pakistan, where over one million people live, a single case has been detected and wastewater detection there and elsewhere in Pakistan indicates real ongoing concern. In Afghanistan, many more cases are circulating, including vaccine-related cases.

Both wild-type and vaccine-related cases can be eradicated through high penetration of vaccination. But that is where the problems begin.

There are many reasons why citizens of Pakistan have seen declining rates of immunization, but one of them relates to the U.S. Government's efforts to find Osama bin Laden by using a fake vaccination program to identify bin Laden's location. In 2014, the US government promised not to do such a thing again, but the damage was done. There are, obviously, many more reasons for individuals to become skeptical. But this one stings a lot.

This week the Taliban, the de facto ruling entity of Afghanistan, banned most of their polio vaccination program. This, too, is a very concerning move.

If we are to have successful vaccination programs, whether we are talking about in the U.S. Or Pakistan or adjoining Afghanistan, we need to make certain that politics are minimized and the public's questions are answered early and often.

For the moment, Pakistan is engaging in a truly massive vaccination campaign as the rest of the world watches and hopes for a quick reversal of the current outbreak. But Afghanistan has paused most of its efforts, with worsening data.

We can eradicate polio. But it will require true global cooperation. One nation alone can't do it.

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