As more people are vaccinated and diseases disappear, they forget how bad those diseases are, skip or delay getting their vaccines, and trigger outbreaks. Photo by WHO
They aren’t, but you can kind of understand why they might think that with a disease like polio, when they might never actually have known anyone to have the disease.
What Is the Morbidity/Mortality Rate of the Polio Vaccine vs the Wild Virus?
Still, even though polio is under good control and close to being eradicated, the risk/benefit ratio clearly favors getting vaccinated and protected.
That’s because the polio vaccines are very safe and if we stopped vaccinating, polio could come back.
In fact, morbidity/mortality from polio vaccines are decreasing, as we are using much less oral polio vaccine (OPV) in the transition (OPV cessation) to just using inactivated polio vaccine (IPV).
“Over the past ten years, more than 10 billion doses of OPV have been given to nearly three billion children worldwide. More than 16 million cases of polio have been prevented, and the disease has been reduced by more than 99%. It is the appropriate vaccine through which to achieve global polio eradication.”
OPV Cessation
And while most developed countries already use IPV, those that are still using OPV recently switched from a trivalent (tOPV) to a bivalent (bOPV) form of OPV. We could do this because type 2 poliovirus has already been eradicated (2015)!
Of course, the issue with the OPV vaccines is that they rarely cause vaccine-associated paralytic polio (VAPP) and circulating vaccine-derived polioviruses (cVDPV).
Fortunately, this is even less common with bOPV.
As this chart from the WHO shows, polio vaccines are very safe.
So morbidity (getting sick)/mortality (dying) from polio vaccines is low.
There were only 31 cases of wild polio in 2018, in Afghanistan and Pakistan, and an additional 102 cases of cVDPV in 7 countries.
What about morbidity/mortality from polio?
“As recently as 30 years ago, wild poliovirus paralysed more than 350 000 children in more than 125 countries every year. In 2018 there were fewer than 30 reported cases in just two countries – Afghanistan and Pakistan.”
“Zero polio transmission and health for all”, WHO Director-General gives new year’s wish to the people of Afghanistan and Pakistan
With a 99.9% drop in polio cases since 1998, your risk of getting polio in most parts of the world is very low, but you still have to consider both the morbidity/mortality of polio in the pre-vaccine era and the risk of polio returning if we stop vaccinating before it is eradicated.
What about the idea that you don’t have to worry about polio because only 1% of kids with polio developed paralysis?
“The mortality rate for acute paralytic polio ranges from 5–15%.”
Disease factsheet about poliomyelitis
Well, when everyone gets polio, even 1% is a lot.
With such a safe vaccine, why put your kids at risk of getting polio?
Do you even understand what the risks are?
No, it isn’t just the risk of wild polio in Afghanistan and Pakistan.
Since the oral polio vaccines shed, if you are unvaccinated, in addition to the risk of wild polio, there is a small risk of getting circulating vaccine-derived polioviruses (cVDPV) if you are not vaccinated and protected. No, it is not a big risk, as there were only 102 cases of cVDPV in 7 countries in 2018, but it isn’t zero either.
And the other big risk is that if enough folks stop getting vaccinated, taking their chances hiding in the herd, polio will come back and our chance to eradicate another vaccine-preventable disease will fail.
More on the Morbidity and Mortality Rates of Polio
There is a lot more interest in polio these days, but not because we are close to eradicating this deadly disease, but rather because of the emergence of cases of acute flaccid myelitis (AFM).
Although the cases have a different cause, the symptoms of AFM are the same that we used to see during the outbreaks of polio that used to hit each summer in the pre-vaccine era.
Polio
Surprisingly, in most people, the poliovirus doesn’t actually cause any symptoms. They simply have an asymptomatic infection.
In some others, the poliovirus causes flu-like symptoms, including a fever, sore throat, nausea, and a headache – symptoms that last about 3 to 5 days.
Much more rarely, the poliovirus causes meningitis or paralysis.
It is these cases of paralytic polio that most people are aware of and that panicked parents during summers in the 1940s and 50s.
In addition to respiratory problems (think iron lungs), polio causes muscle atrophy. (CC BY-NC 4.0)
After having flu-like symptoms, those kids who would develop paralytic polio can develop pain and then flaccid paralysis.
“The most severe form, paralytic poliomyelitis, which is seen in less than 1% of patients, presents as excruciating episodes of pain in back and lower limbs. In children, the disease may present in biphasic form—a period of prodrome followed by a brief symptom-free period of 7 to 10 days and then appearance of asymmetrical paralysis of limbs. Flaccid paralysis is the hallmark with loss of deep tendon reflexes eventually.”
Mehndirattta et al on Poliomyelitis Historical Facts, Epidemiology, and Current Challenges in Eradication
Of course, polio wasn’t always called polio.
Other names have included infantile spinal paralysis, infantile paralysis, Heine-Medin disease, poliomyelitis anterior acuta, and acute anterior poliomyelitis.
The first use of the name “polio” came from Adolph Kussmaul, with his use of the term poliomyelitis anterior acuta, which was derived from the Greek polios “grey” and myelos “marrow” and itis “inflammation.” It was because he knew that it was caused by inflammation of the spinal cord gray matter, even if he didn’t know why.
Polio History
Polio didn’t just suddenly appear in the middle of the 20th century though, it was likely around for ages.
That one of this Ancient Egyptian priest’s legs is smaller than the other and he uses a staff to walk could suggest that he had polio.
In addition to an Egyptian funeral stele (a stone slab used as a monument) portraying Roma the Doorkeeper from 1500 BCE that suggests he had paralytic polio, archeologists have found evidence of polio in skeletons as far back as the Neolithic period.
A medical book from 1789 likely describes people with polio.
Still, we don’t really know how long polio has been around and we don’t know why we began to see more cases in the mid-20th Century, although there are theories, including, ironically, about hygiene. While we often credit improved sanitation and hygiene for helping to reduce mortality from many diseases, some think that this actually set us up for polio outbreaks, as we were no longer exposed as infants, when we still had some maternal immunity.
The one thing that we do know is that we are on the verge of eradicating polio, as there are very cases now, in just a few countries.
Polio Timeline and Milestones
In addition to the more ancient discoveries about polio, there is a lot to learn about vaccines and vaccine-preventable diseases if we look at the major milestones of this important disease.
Although in the end it is a success story, the road to figuring out what caused polio symptoms and how polio could be prevented was very long.
Michael Underwood describes what is thought to be paralytic polio in his book A Treatise on the Diseases of Children, with General Directions for the Management of Infants from Birth in a section on “Debility of the Lower Extremities” (1789)
first reported outbreak of polio in Worksop, England (1835)
Jacob von Heine, head of an orthopedic hospital in Germany, publishes a monograph that describes 29 cases of paralytic polio, and actually attributes the condition to inflammation of the anterior horns of the spinal cord, although the cause was still not known (1840)
first use of the term poliomyelitis by Adolph Kussmaul (1874)
Nils August Bergenholtz reports on an outbreak of paralytic polio in Sweden (1881)
Karl-Oskar Medin, a pediatrician who reported on a polio epidemic in Sweden (1887), later presents his findings at the Tenth International Conference in Berlin (1890)
the first major outbreak in the United States is documented in Rutland County, Vermont and causes 132 cases of paralysis and 18 deaths (1894)
Ivar Wickman tracks cases of polio during an epidemic in Sweden in 1905 and was the first to suggest that polio was contagious and that you could get it from “those afflicted with the abortive type” (1907)
although they don’t actually identify the poliovirus, Dr. Karl Landsteiner and Dr. Erwin Popper identify that a virus causes polio when they inject material from the spinal cord of a child who had recently died with polio into the peritoneum of two monkeys, both of which soon developed paralytic polio (1908)
Simon Flexner, first discovers polio antibodies (1911), but unlike other researchers at the time, pushes the theory that polio was spread by the olfactory route, instead of the fecal-oral route, which was why we saw the development of nose sprays, etc., to try and prevent polio, none of which worked of course
a large polio epidemic in the United States causes at least 27,000 cases and 6,000 deaths (1916)
Philip Drinker and Louis Agassiz Shaw invent the first iron lung, the Drinker respirator (1929)
Frank M. Burnet and Jean Macnamara proposed that there were antigenically different strains of poliovirus (1931)
John R. Paul and James D. Trask help figure out how polio was spread by identifying the polio virus in human waste and sewage samples (1932)
Maurice Brodie and John Kolmer have unsuccessful field trials of early polio vaccines, including allergic reactions and vaccine induced polio because of poor attenuation (1935)
Sister Elizabeth Kenny establishes a clinic in Australia to treat polio survivors (1932) and later publishes her treatment recommendations, Infantile Paralysis and Cerebral Diplegia (1937)
the National Foundation for Infantile Paralysis is founded by FDR to stop polio (1937)
Carl Kling found traces of the poliovirus in the Stockholm sewage system (1942)
the Sister Kenny Institute is built in Minneapolis, as her treatment methods become widely accepted after years of controversy (1942)
the U.S. Army Neurotropic Virus Commission, including Albert Sabin, gets a grant from the NFIP to study polio in North Africa (1943)
Isabel Morgan actually developed the first inactivated polio vaccine, but only tested it on monkeys (1949)
John Enders, with T. H. Weller and F. C. Robbins, received the Nobel Prize in 1954 for their work on the cultivation of the poliomyelitis viruses (1949)
David Bodian creates the monkey model using field isolates of poliovirus and with Jonas Salk, identifies the three poliovirus serotyes (1950s)
Hilary Koprowki develops the first oral, live polio vaccine, (1950) although Sabin’s vaccine eventually gets licensed because it is thought to be less neurovirulent in monkeys and undergoes more testing
there are 58,000 cases of paralytic polio in the United States (1952)
Renato Dulbecco, with Marguerite Vogt, successfully grows and purifies polio virus (1952)
the Polio Pioneers vaccine field trial, led by Thomas Francis Jr., that proves that Jonas Salk’s polio vaccine is safe and effective begins (1954)
improperly inactivated polio vaccine from Cutter Laboratories (Cutter Incident) causes 40,000 cases of polio, 200 cases of paralysis, and kills ten people (1955)
Albert Sabin develops the first live, oral polio vaccine, which replaced Jonas Salk’s inactivated polio vaccine (1961)
that polio survivors can develop new, late complications or post-polio syndrome begins to get reported (1969)
last endemic case of polio in the United States (1979)
the National Foundation for Infantile Paralysis officially changes its name to the March of Dimes Birth Defects Foundation (1979)
the World Health Assembly adopts a resolution for the worldwide eradication of polio by 2000 and the the Global Polio Eradication Initiative is launched (1988)
last imported case of polio in the United States (1993)
the WHO Region of the Americas is declared polio free (1994)
“last” case of VAPP that was acquired in the United States (1999)
last case of wild poliovirus type 2 (1999)
the WHO Western Pacific Region is declared polio free (2000)
the United States switches back to using the an inactivated polio vaccine because of concerns over VAPP (2000)
the WHO European Region is declared polio free (2002)
outbreak of vaccine derived polio among a group of unvaccinated Amish in Minnesota (2005)
last case of VAPP that was acquired outside the United States, an unvaccinated 22-year-old U.S. college student who became infected with polio vaccine virus while traveling in Costa Rica in a university-sponsored study-abroad program (2005)
last case of VAPP in the United States, a patient with a long-standing combined immunodeficiency who was probably infected in the late 1990s (2009)
last case of type 3 poliovirus (2012)
seasonal reports of acute flaccid myelitis in the late summer and early fall, which might be caused by a non-polio enterovirus, are reminiscent of polio epidemics in the early part of the 20th century (2014)
type 2 poliovirus eradicated (2015)
Bob Sears says that it is okay to delay the polio vaccine on his alternative vaccine schedule because “we don’t have polio in the United States” (2015)
a global switch from trivalent OPV to bivalent OPV in routine immunization programs (2016)
polio remains endemic in just two countries, Afghanistan and Pakistan (2018)
So it should be clear, that despite what some folks think, polio wasn’t conquered overnight. And Salk and Sabin obviously had a lot of help, although those are the names we most commonly hear connected with polio eradication.
“Until poliovirus transmission is interrupted in these countries, all countries remain at risk of importation of polio, especially vulnerable countries with weak public health and immunization services and travel or trade links to endemic countries.”
Global Polio Eradication Initiative on Endemic Countries
Most people understand that polio vaccines have helped to control and get us close to eradicating polio.
Many even know that there are two types of polio vaccine – the inactivated Salk vaccine and the live Sabin vaccine.
Some might even know that there are actually three strains of polio virus that we have traditionally gotten vaccinated against, and that one of those strains, type 2, has already been eradicated.
“In April 2016 a switch was implemented from trivalent OPV to bivalent OPV in routine immunization programmes.”
OPV Cessation
That’s why we have switched to using a bivalent OPV which only contains type 1 and 3 serotypes.
Contaminated Vaccines in India
What does all of this have to do with the news of contaminated vaccines in India?
“At least three batches of polio vaccines containing 1.5 lakh vials have been found contaminated with type 2 polio virus, putting at risk India’s “polio free” status as children born after April 2016 — when the type 2 virus was withdrawn worldwide including in India — do not have immunity to this particular virus, sources said.”
Unfortunately, some contaminated vaccines were actually administered to children in the Indian states of Maharashtra, Telengana, and Uttar Pradesh before the contamination was discovered.
Will these kids get polio?
No, as the vaccines weren’t contaminated with wild polio virus.
It seems that Bio-Med Private Limited was still producing and distributing polio vaccine with the type 2 vaccine virus, even though this type of vaccine was discontinued a few years ago.
Why?
We will hopefully find out, as the managing director of Bio-Med Pvt Ltd has been arrested, but we don’t know yet.
We do know that there is little risk from these vaccines and they won’t put India’s “polio free” status at risk.
Why would there be any risk from kids getting an extra vaccine virus strain?
It’s because the type 2 strain of polio is the most likely to cause cVDPV, or outbreaks of polio that are actually caused by the polio vaccine.
Fortunately, these outbreaks are very rare.
A dose of IPV is the backup plan to make sure any problems with the switch to bOPV doesn’t end up in a tragedy.
But kids in the area are at even less at risk from these “contaminated” vaccines because as part of the plan to switch from trivalent oral polio vaccine (tOPV) to bivalent oral polio vaccine (bOPV), they likely got a dose of IPV, which includes protection against all three polio virus strains.
Not that this means that it isn’t a problem that a company was making and distributing a vaccine that kids shouldn’t have been getting.
That is terrible!
It just isn’t as big a danger as some folks are making it out to be. It is extremely unlikely that there will be any cases of polio in India, and definitely not a resurgence of polio because of these vaccines, as some have suggested.
The real risk will be that an isolated event will scare folks away from getting vaccinated and protected, even though we know that these events are rare and that vaccines are safe.
As most folks know, neither the DPT nor OPV vaccines are used in the United States.
Pope Francis helped launch a polio vaccine campaign when he visited Mexico in 2016.
That they are still used in other countries likely raises some questions for those folks that get them.
Why Are the DPT and OPV Vaccines Still Used in Some Countries?
As I am sure you have guessed, there is no conspiracy about the continued use of these vaccines in other parts of the world. We aren’t getting rid of old stocks of vaccines or using cheaper vaccines in poorer parts of the world.
So what’s the reason?
To understand why they are still used in other countries, it helps to understand why they aren’t used here.
Remember that the DPT vaccine, which protects folks against diphtheria, pertussis, and tetanus, came under attack in the 1970s and 80s as some folks blamed the vaccine for causing vaccine injuries, including seizures and encephalopathy. It didn’t, but we still got a new vaccine, DTaP, which doesn’t seem to work as well.
“Although concerns about possible adverse events following their administration have led to the adoption of acellular pertussis vaccines in some countries, whole-cell pertussis vaccines are still widely produced and used globally in both developed and developing countries. Whole-cell pertussis vaccines that comply with WHO requirements, administered according to an optimal schedule have a long and successful record in the control of whooping cough. Furthermore, the excellent efficacy of some currently available whole-cell pertussis vaccine has also been shown, not only in recent clinical trials, but also on the basis of the resurgence of disease where vaccination has been interrupted or when coverage has markedly decreased. Therefore, WHO continues to recommend whole-cell pertussis vaccines for use in national immunization programmes.”
WHO on Recommendations for whole-cell pertussis vaccine
The WHO now recommends that if countries do switch to DTaP, the acellular pertussis vaccine, they should be prepared to add additional periodic booster doses and immunizations during pregnancy, which may still “may not be sufficient to prevent resurgence of pertussis.”
The OPV vaccine, on the other hand, was replaced because it can rarely cause vaccine-associated paralytic polio (VAPP) and circulating vaccine-derived polio virus (cVDPV). Of course, it does it at much lower rates than wild polio virus, so until polio is well controlled, the benefit of using OPV outweighs the risk. In addition to being less expensive and easier to use, OPV has the benefit over IPV of providing better herd immunity.
At some point, as we did in the United States in 2000, countries make a switch to the IPV vaccine.
In 2016, remaining countries that use OPV switched from trivalent OPV to bivalent OPV, because wild polio virus type 2 was eradicated in 1999. Once the remaining two types are eradicated, we can stop using the OPV vaccine altogether.
Until then, countries either use:
OPV plus one dose of IPV
sequential IPV-OPV schedules – high vaccine coverage and low risk of wild polio importation
IPV only schedules – sustained high vaccine coverage and very low risk of wild polio importation
So there is no conspiracy. These vaccines are safe and they work.
