Polio eradication: A saga of Mother Nature, politics and anti-vaxxers
In 1983, the Pan American Health Organization (PAHO) held a major conference reviewing the situation with poliomyelitis in the Americas. The conference was noteworthy for the presence of both Albert Sabin and Jonas Salk because they had rarely attended a conference where both were present. There had been a longstanding unfriendly dispute and competition over which vaccine was the better vaccine — Sabin’s live oral poliovirus vaccine (OPV) or Salk’s injected inactivated poliovirus vaccine (IPV). As the two giants in the field each spoke, Sabin went first (alphabetical order was chosen), and when Salk got up to speak, his opening comment was, “Let it go on record that Dr. Sabin and I are in agreement — there is no need for two different vaccines.” While we are using quotation marks, it is possible this is more of a paraphrase from Dr. Pollack’s long-term memory cells of the event. This meeting served as the foundation for initiating a regional effort to interrupt poliovirus transmission in the Americas. The goal of polio eradication in the Americas was declared in May 1985.
Success in the Americas
Following this, the Americas region waged a comprehensive campaign, strengthening laboratory support, improving case identification and using the strategy of national and subnational vaccination campaigns. In addition, “mop-up” activities were initiated in 1989, aimed at increasing vaccination coverage in locations surrounding those areas where cases were identified and where district coverages were identified as inadequate. With rapid success, the last case of wild poliovirus (WPV) reported was in Peru in August 1991, and the eradication of polio in the Americas was officially declared on Aug. 20, 1994.
The rest of the world
In the 3 years following the declaration of the Americas regional eradication effort, the groundwork was laid for implementation of a global effort to eradicate polio. In 1988, the World Health Assembly passed a resolution to eradicate polio globally. Given the successes in the Americas, there was enthusiasm and commitment for a sure thing: to make polio the second human vaccine-preventable disease ever to have been eradicated, after smallpox. (Rinderpest, a disease of animals, also has been eradicated.)
There are three known strains of WPV — types 1, 2 and 3. WPV2 was declared eradicated on Sept. 20, 2015, with the last known case having been detected in Aligarh, northern India, in 1999. The eradication of WPV3 was celebrated on International Polio Day last year (Oct. 24). Only one more serotype to go.
What could go wrong?
Mother Nature had other plans for the polio eradication effort. In the 1980s when polio eradication was first declared, it was known that there was the rare occurrence of paralytic disease in recipients of the vaccine and in susceptible contacts of recent recipients. Laboratory support in those days was able to differentiate between vaccine viruses and wild polioviruses. But it wasn’t until genetic testing in laboratories became available that we were able to identify circulating vaccine-derived polioviruses (cVDPVs). cVDPVs are a subgroup of polioviruses that started out as oral poliovirus vaccine viruses, but after multiple passages through human gastrointestinal tracts, reverted back to increased neurovirulence. This was especially likely to occur in settings where sanitation is poor. This cVDPV subgroup of VDPVs was capable of circulating in communities similar to the way WPVs are transmitted.
We are now in 2020, 32 years following the declaration of the goal of global polio eradication, and as of Dec. 17, 2019, there were a total of 125 WPV1-associated cases of acute flaccid paralysis (AFP) confirmed with dates of onset since Jan. 1, 2019, with all cases reported from Afghanistan (24) and Pakistan (101). But that’s not all. As of Dec. 17, 2019, there were a total of 241 cVDPV-associated cases of AFP confirmed with dates of onset since Jan. 1, 2019. In 2016, there were a total of 37 cases of AFP associated with WPV1 and five cases of AFP associated with cVDPV infection.
The obvious question is, “What happened?” Why the resurgence of both WPV- and cVDPV-associated disease?
A simple answer is that there has been a decrease in vaccination coverage, leaving pockets of susceptible people where a poliovirus (either WPV or cVDPV) can circulate and lead to AFP in susceptible individuals. Note that to develop a cVDPV infection, the vaccine virus needs to circulate among susceptible individuals, with multiple passages through different individuals until there are the genetic changes that are associated with reversion to neurovirulence.
First, it is important to note that many of the areas affected by decreasing vaccination coverage are experiencing civil strife, where it is unsafe for government-sponsored vaccination teams to enter. Adding to this is that, over the past 10 to 15 years, there have been continually increasing anti-vaccination rumors circulating in conservative tribal areas in the three remaining WPV-endemic countries (Afghanistan, Pakistan and Nigeria). The vaccine has been rumored to contain pork, a forbidden food in these areas, and to have agents that cause sterility. To make matters worse, the global anti-vaccination movement has reached these countries, and previously highly vaccinated areas have been succumbing to the fake news prevalent on social media platforms.
Then there are the politics of health combined with campaign fatigue. Communities rebel, not having seen much polio in recent years, but seeing vaccination campaigns going from house to house multiple times a year while they perceive other more pressing health problems such as diarrheal disease and other waterborne illnesses. These communities, stirred on by oppositional parties, feel the governments are failing them and their needs and are following international goals without benefiting them. Thus, they avoid vaccination.
The result of these factors is low vaccination coverage caused by hiding children when vaccinators come to their doors or using markers to identify their children as having already been vaccinated.
Adding insult to injury
But there is more information of importance. Through the years, it has become apparent that the OPV type 2 vaccine virus was the more likely virus to convert to a cVDPV. Based on this and the declaration of eradication of the WPV2, there was decision to drop the OPV2 component in the vaccination programs and campaigns worldwide in April 2016, changing to a bivalent vaccine containing the OPV1 and OPV3 viruses only, and to have all countries introduce a single dose of the trivalent IPV to provide poliovirus type 2 protection. But, and this is a big but, the supply of IPV did not meet the demands, and not all countries had been able to implement the dose of IPV into the routine schedules. In fact, the last two countries to introduce IPV were Mongolia and Zimbabwe, which introduced IPV in 2019.
As mentioned earlier, in 2016, there were a total of five cases of cVDPV polio, two of which were due to cVDPV2 — one each in Pakistan and Nigeria, both countries with known pockets of lower than optimal vaccination coverage and with WPV1-associated cases during 2016. In 2017, there were 96 cases of cVDPV-associated polio, all of which were due to cVDPV2 infections related to outbreaks in the Democratic Republic of the Congo (DRC) and Syria, both areas of civil unrest with resultant suboptimal vaccination coverage. In 2018, there were a total of 105 cases of cVDPV-associated polio, of which 71 (67.6%) were due to cVDPV2 infections and involved outbreaks in Nigeria, the DRC, Somalia, Niger and Mozambique. As of Dec. 17, 2019, there have been 241 cases of polio due to cVDPV, of which 233 (96.7%) are due to cVDPV2. Each outbreak of cVDPV2 is controlled by campaigns with monovalent OPV2, thereby flooding the environment again with fresh OPV2 virus to begin a new potential pathway to cVDPV2. Although there is a novel OPV2 (nOPV2) in the pipeline that theoretically is less likely to undergo neurovirulence reversion, it has been tested on only small numbers of individuals with single passages of the vaccine as opposed to the millions who would be receiving it, a background needed to definitely identify rare unexpected events. And the number of confirmed cases of cVDPV2-associated paralytic disease keeps climbing; in the 2-week period from Dec. 4, 2019, to Dec. 17, 2019, there were 46 newly confirmed cases of cVDPV2-associated disease.
The international war on poliomyelitis has been enormously successful. There were thousands of cases of AFP yearly in the United States in the 1900s, with many more elsewhere in the world. Therefore, by any criteria, the vaccination programs have been a huge success. But the last mile to eradication of the disease will be extremely difficult. We are now at the point of recognizing we are in a vicious circle of reduced vaccination coverages due to civil unrest, the anti-vaccination movement and rumors, population campaign fatigue and antigovernmental political malfeasance. Enter Mother Nature and her diabolic plan for the OPV neurovirulence reversions. Is it time to eliminate OPV and go the route of exclusive IPV? Was Salk prophetically correct with his comment at the 1983 meeting convened at PAHO?
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- For more information:
- Donald Kaye, MD, MACP, is a professor of medicine at Drexel University College of Medicine, associate editor of the International Society of Infectious Diseases’ ProMED-mail, section editor of news for Clinical Infectious Diseases and an Infectious Disease News Editorial Board Member.
- Marjorie P. Pollack, MD, is deputy editor of ProMED-mail and an independent consultant medical epidemiologist with a focus on developing world issues following CDC training. She is based in New York.
Disclosures: Kaye and Pollack report no relevant financial disclosures.