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The Dream Of Wiping Out Polio Might Need A Rethink
The global campaign to eradicate polio has been incredibly successful except in one key way: It hasn't actually eradicated polio.
Some prominent scientists who've spent their entire careers battling polio are now saying it's time to rethink the multi-billion dollar fight against the disease.
When the Global Polio Eradication Initiative was launched in 1988, the goal was to extinguish polio by the year 2000. At the time, polio was still paralyzing hundreds of thousands of people a year, and some cases were even fatal.
In the first three months of this year there have been 15 cases, total, in the entire world.
Even such a relatively small number of cases, say some specialists, shows that the goal of wiping out the disease may be elusive.
Countries, particularly in Africa, were declared polio-free only to have polio pop up again years, even decades, later. Last year, the United States, which had officially eliminated polio in 1979, had a case of the paralytic disease. The virus has also been found in sewage samples in London, Finland and Jerusalem, all places where it supposedly was extinguished decades ago.
Where the cases areThe U.S. Case and most of the current outbreaks in Africa (which was declared a polio-free continent in 2020) are linked to vaccine-derived strains of the virus. These strains were originally part of oral polio vaccine. They were shed in human stool from those who'd been inoculated and mutated in the wild, regaining strength and becoming just as dangerous as the original virus.
Health officials were aware that the virus in the oral vaccine could mutate, says Paul Offit, director of the Vaccine Education Center at the Children's Hospital, Philadelphia, and a professor of pediatrics at the University of Pennsylvania School of Medicine.
Despite this concern, the oral vaccination campaigns proceeded. "We were seduced by the fact that it was cheap. It caused contact immunity. It was easy to give," Offit says. "And so we thought, 'We can eliminate this this disease in the world.' "
Last year there were only 30 cases of wild polio detected while there were nearly 800 cases of vaccine-derived polio. Of the 15 cases reported in the first quarter of 2023, 14 are from strains of the virus that mutated from the oral polio vaccine used in lower-income nations.
"We released the dragon and the dragon was the circulating vaccine-derived polio viruses," Offit says.
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So in an ironic twist, countries are now launching emergency vaccination campaigns to protect children from outbreaks linked to earlier vaccination campaigns.
How vaccine-derived polio spreadsPublic health officials knew early on in the eradication effort that the oral polio vaccine could spread far beyond the child who was initially vaccinated. This in fact was one of the benefits of the polio drops. It spread like other viruses in the community and could immunize unvaccinated kids in the neighborhood who were exposed as kids pooped out – or "shed" — the vaccine into sewage. In places with poor sanitation, the sewage mixes with drinking water. When unvaccinated kids consume that water, they gain immunity.
But the virus spreading in waste water can also cause paralytic disease. That is most likely what happened last year in the case of an unvaccinated man in New York being paralyzed by a vaccine derived strain of the virus. Offit says this case is concerning and shows that vaccine-derived polio virus is probably widespread even in the United States.
People who've been vaccinated with the injectable form of the polio vaccine, as have most in the U.S., can still carry and spread the virus to unvaccinated individuals.
"For every 2,000 people who are infected with this strain, one will be paralyzed. So he clearly is the tip of a much bigger iceberg," Offit says. The virus was also found in wastewater samples in Rockland County, N.Y. Near where the man lived. Now the CDC has committed to check sewage systems nationwide to see if there is more polio virus circulating in the United States. "I would be surprised if there weren't," Offit predicts.
Despite the attention the New York polio case attracted last year, most of the current outbreaks are in low-income countries which use the less-expensive oral polio vaccine and where vaccination rates are often incredibly low. In some places only 5% of kids are fully up to date on the childhood immunizations.
In a perfect world, health experts say they'd like everyone would get the more expensive polio shot which is incapable of mutating into a dangerous, circulating virus.
But Aidan O'Leary, who heads up the Global Polio Eradication Initiative (GPEI) at the World Health Organization, points out that the polio elimination effort is happening in a world that's far from perfect.
The worst outbreaks of vaccine-derived polio right now, he says, are in parts of Nigeria, Somalia, the Democratic Republic of Congo and Yemen. Last year there were 461 cases of paralytic polio in the DRC — more than in any other country in the world.
"As you're probably aware these locations are fairly complicated places to operate," says O'Leary. "There's political instability, insecurity and protracted, complex humanitarian emergencies." He says these hot spots are the "engines" driving the outbreaks of vaccine-derived polio globally.
In many of these remote, conflict-ridden parts of the world, O'Leary says the options for polio vaccination are very limited. "The health systems are kind of, I would say, skeletal in nature. Childhood immunization rates can be as low as 5%."
Mass immunization campaigns with the more expensive yet safer injectable vaccine, he says, are nearly impossible in some of these places. There simply isn't the infrastructure or trained medical staff to carry out such campaigns.
"In places like northern Yemen, in places like south central Somalia, the essential immunization systems are suboptimal and the issue is about building [public health] capacity," he says. "But these are not quick fixes, not over three years, not over five years, not over ten years. It takes a long, long time to really make the investments to strengthen these health systems."
And if polio is left unchecked in some of these places, it not only affects local kids but these areas become reservoirs from which the virus spreads around the world.
The debate over anti-polio strategies"Do we continue to review and adjust tactics? The answer is, of course, yes," O'Leary says. In fact a new version of the oral polio vaccine that is less likely to mutate was introduced in 2021. There are attempts in many places to mix the oral and the injectable vaccines in hopes of providing broader protection from the virus.
"But the backbone of our approach is really this house-to-house coverage [with oral vaccine], O'Leary says, "It has been demonstrated over time is that this is the best means of ensuring that we're able to reach each and every child. And that is fundamentally the key to actually achieving the goals we've set for ourselves."
Konstantin Chumakov disagrees. He's the former associate director for research at the U.S. Food and Drug Administration's Office of Vaccines and has been involved in the global effort polio against polio for decades. "If we keep doing the same thing, expecting different results, that's a recipe for failure," he says.
Zulfiqar Bhutta, the founding director of the Institute for Global Health and Development at the Aga Khan University in Pakistan, also believes that the house-to-house campaigns can't go on forever.
"We have had these campaigns for such a long time," Bhutta says. "Remember, the global eradication program started in 1988 and people kept asking, why are you coming every few months with these vaccine doses that we have already had and then kids are getting the paralytic polio despite the vaccine."
There's another reason to rethink the goal of no more vaccines: If human immunity to polio disappears, says Chumakov, the virus could become an incredibly dangerous biological weapon.
"I don't envision the circumstances where we can stop vaccinating, and say, 'Okay, there's no more polio. Forget it.' Just for one simple reason: Polio can be made in a lab in two weeks," he says. More than 20 years ago researchers at the State University of New York, Stony Brook, cooked up infectious polio from scratch using publicly available data.
One of the fundamental goals of the Global Polio Eradication Initiative is to wipe the polio virus off the face of the earth (similar to the way smallpox was eradicated) and then do away with polio immunization programs entirely, says Chumakov. But because the virus can be made in a lab, this goal is unrealistic, he says. He believes that "you cannot stop" polio immunizations: "No, they will have to continue forever, everywhere, indefinitely."
"And there's no reason to stop," adds Chumakov, who is now an adjunct professor at George Washington University and the University of Maryland. But there is a different way to administer the doses. He says. Along with colleagues from the Global Virus network, Chumakov co-authored an article in the New England Journal of Medicine in February, arguing that resources being used to attack polio should instead be folded into programs that beef up all routine childhood immunization programs globally.
Bhutta says polio vaccine — both oral and injectable in an ideal world — should be given along with other childhood immunizations
O'Leary at GPEI says that they fully support rolling polio into routine childhood health programs in places where the health-care systems have the capacity to do it. The problem is that there are still places in the world where that isn't possible. And polio finds those places. It settles in. It multiplies.
"Viruses always find a way," adds Offit from the Children's Hospital of Philadelphia. "Their goal is to be transmitted from one person to the next to the next. And they'll do whatever they can to get there, whether it's polio or SARS-CoV-2 or the common cold virus or influenza virus. They will do what they have to do to survive. And they're smarter than we are."
The History Of The Polio Vaccine
On April 12, 1955, virologists announced that they'd developed a safe and potent vaccine against polio, the deadly, paralyzing disease that then tormented thousands of individuals in the U.S. Setting off a series of concentrated vaccination campaigns in the country and abroad, the announcement sowed the seeds for a polio-free future.
Today, 68 years after the arrival of the vaccine, the disease teeters on the verge of disappearance. In the U.S., cases of wild, community-circulating polio were wiped out in the 1970s, and since then, they've been banished from almost all corners of the world.
So, in honor of its April announcement, here's what you'll want to know about the history of the polio vaccine.
The Plague of PolioThough the virus that causes polio has circulated throughout human history, it wasn't until the 1900s that the poliovirus prompted seasonal spates of infections. The first of these outbreaks to occur in the U.S. Took place in Vermont in the 1890s, infecting 132, paralyzing 58, and killing 18. And waves of worse outbreaks only followed, troubling the population (and particularly the young) for the next 60 years or so.
The reason for the sudden onset of these seasonal, summer outbreaks remains a mystery. Some specialists see the creation and circulation of stronger strains of the poliovirus as the culprit. Others credit improving sanitation systems in the U.S., which prevented people from increasing their immunity to the virus in their infancy.
That said, regardless of the reason, the sudden appearance of an annual polio season was devastating. In 1952, the single worst wave of the disease infected 60,000 individuals in the U.S., many of whom were left with canes, crutches, wheelchairs and full-body breathing apparatuses called "iron lungs" in the aftermath of the surge.
With polio ravaging the population and no cure in sight, an assembly of specialists supported by the National Foundation for Infantile Paralysis set out to fight the virus with vaccines. By that time, the notion of fending off a virus with vaccines was nothing new. But producing a vaccine against polio was still a tricky task, requiring an intimate knowledge of the transmission of the virus.
Read More: Learning From the World's Worst Diseases
The Pathology of PolioPolio, or poliomyelitis, is an intestinal infection caused by the poliovirus, which passes from person-to-person through the ingestion of the feces of an infected individual.
The infections are mostly mild, involving symptoms such as fever, fatigue and nausea. But in around 1 in 200 infections, the virus travels to the nervous system, where it destroys the neurons that direct muscle movement. When this occurs, the virus can cause permanent paralysis and sometimes death, whenever the muscles within an individual's airways are adversely affected.
Throughout the 1940s, researchers learned a lot about the poliovirus. In 1949, a team discovered that there were three types of virus in circulation, including PV1, PV2 and PV3, which would need to be targeted and treated by a vaccine on an individual basis. That same year, another team discovered that these three types of virus could all be cultivated artificially, which would supply a stream of poliovirus, safely and consistently, from which a potential vaccination could be created.
Read More: The Deadly Polio Epidemic and Why It Matters for Coronavirus
Salk's Polio VaccineArmed with the knowledge of the three types of poliovirus, as well as a steady supply of all three, American virologist Jonas Salk developed the first promising vaccine against polio in 1952. After several small trials, the vaccine was tested in the Francis Field Trial, which was then the most massive medical field test in the U.S.
Named after Thomas Francis, the administrator of the test, the trial involved almost 2 million individuals who received injections of a vaccine or a placebo, or who received nothing at all. After observing the participants to determine whether the vaccine reduced their chances of contracting polio, Francis concluded in April 1955 that the vaccine was 60 to 70 percent effective against PV1 and 90 percent effective against PV2 and PV3.
Breaking from the traditional process of vaccine development, Salk's vaccine did not contain any active strains of the virus that it intended to defeat. Instead, it contained only inactivated strains of the virus, incapacitated by formaldehyde, which could induce antibodies without inducing infection. As one of the first pioneers of this type of vaccine, Salk was convinced that these strains were as potent as active strains, but much more secure when included in vaccinations.
The results of the trial inspired the immediate approval of the vaccine. Soon, millions of vaccinations were transported throughout the U.S., where they were distributed, first and foremost, to the "polio pioneers" who participated in trials without receiving doses of the drug themselves. Following this initial wave of vaccinations, infections dipped, and deaths decreased by 50 percent after a single year.
Sabin's Polio VaccineWithin two years of the announcement, annual infections from polio plummeted to around 5,600 in the U.S. Within six years of the announcement, infections plunged to 160. This additional drop in infections was due to the development of an alternative, active version of the vaccine, developed by virologist Albert Sabin and made available to the public in 1961.
While Sabin acknowledged that the inactive strains included in Salk's vaccine could induce antibodies temporarily, the virologist thought that an active virus was required to raise antibodies that really stuck around. As such, Sabin studied an assortment of active poliovirus variants, searching for strains which were too weak to cause serious symptoms but were strong enough to evoke an enduring antibody response.
By 1961, Sabin found three of these attenuated strains, and incorporated them in an active vaccine for polio. Administered orally, by being dropped onto the tongue or infused in sugar, Sabin's active vaccine was simple and affordable to administer. Once approved, it immediately supplanted Salk's injected vaccine, becoming the most popular method of protection against polio in the U.S.
Polio Vaccines in the U.S.Throughout the virologist's career, Sabin insisted that the chances of contracting paralytic polio from an active vaccine were minimal. But despite Sabin's ideas, almost 110 cases of vaccine-associated polio arose in the U.S. Between 1980 and 1992, occurring when the weakened virus incorporated in the vaccine regained its virulence after ingestion.
In response to these infections, the U.S. Returned to the inactive vaccine in 2000. Since then, all vaccines administered against polio in the country have been inactive, completely removing the risk of contracting vaccine-associated polio.
Read More: What Would Happen If We Didn't Have Vaccines
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