Stumbling Blocks in the Road to Polio Eradication
“Hope lies in dreams, in imagination, and in the courage of those who dare to make dreams into reality.”
- Jonas Salk, American physician scientist and developer of inactivated polio vaccine
“Eradication is a very unforgiving goal—one infection is one infection too many."
- Walter Orenstein, M.D., associate director, Emory Vaccine Center, former director, United States’ Immunization Program
The eradication of a disease means the “permanent reduction to zero of cases worldwide.” Smallpox is the only human infection that has been eradicated, a triumph that resulted from a sustained heroic global vaccine campaign. As I discussed in my Germ Gems post on October 11, 2019, “Eradication of Polio: Stuck in the Red Zone,” poliomyelitis (polio for short) is on the verge of eradication. In this Germ Gems post, I provide an update on the stumbling blocks to eradicating the heinous polio virus (PV).
A synopsis of polio. PV is an RNA virus that is transmitted from person to person by the fecal-oral route. The good news is that it colonizes the gastrointestinal tract only of humans; there are no animal reservoirs. Three PV serotypes have been identified—poliovirus type 1 (PV1), type 2 (PV2), and type 3 (PV3). All three are extremely virulent and produce the same symptoms. (Each of these three PV types is often referred to as a “wild polio virus” and designated respectively as WPV1, WPV2, or WPV3.)
In most people with a normal immune system, PV infection is asymptomatic. In some people, however, gastrointestinal tract symptoms occur, and in a small minority (about 1%) the virus invades the central nervous system, causing paralysis.The case fatality ratio for paralytic polio is 2% to 5% among children and up to 15% to 30% among adolescents and adults.
What polio vaccines accomplished. Polio immunization is one of the greatest public health success stories. For those of us who were children before the advent of polio vaccines, paralytic polio—the crippling form of the disease –is burned into our memories. We saw classmates or playmates crippled by the disease who had to wear braces and use crutches. We knew friends or parents of friends who were sent to special hospitals and lived part of their lives in machines called “iron lungs” in order to survive. The introduction of Jonas Salk’s injectable, inactivated polio vaccine (IPV) in 1955 was an unbelievable game changer. The same can be said about Albert Sabin’s 1961 introduction of the attenuated (weakened) oral polio vaccine (OPV). The introduction and widespread use of these vaccines eliminated polio in the U.S.—the last case occurred in 1979.
The Global Polio Eradication Initiative (GPEI) is an extraordinary international collaboration spearheaded by the World Health Organization (WHO), Rotary International, the US Center for Disease Control and Prevention (CDC), and national governments (with support by the Bill & Melinda Gates Foundation). The GPEI’s goal is to “complete the eradication and containment of all wild and vaccine-related polioviruses, so no child suffers from paralytic poliomyelitis ever again.” Due to the GPEI’s immunization efforts, worldwide cases of polio have plummeted by over 99.99%, from an estimated 350,000 cases in 1988 to 33 cases reported in 2018, and more than 24 million people who would otherwise have been paralyzed by PV are able to walk today.
The stumbling blocks appear. In 2017, only 22 cases of polio were reported worldwide, and it looked like we were on the cusp of eradicating this dreaded disease globally. But then in 2018, the downward trend halted when 33 cases were reported: 21 in Afghanistan and 12 in Pakistan (the only countries where polio remains endemic). And cases in these countries continued to mount. By the end of 2020, more than 200 cases of polio due to the “wild polio virus” (WPV) were recorded. At the same time, another even larger battle began raging against certain strains of PV that are included in the OPV. Such strains had “gone rogue,” that is to say, they mutated and developed the virulence properties necessary to cause nervous system disease, including paralysis. (Note: the OPV has not been used in the U.S. since 2000 or in European countries since 2016.) By the end of 2020, 959 cases of vaccine-associated paralytic polio were reported worldwide outstripping the number of polio cases caused by WPV.
Stumbling block no. 1: Vaccine-associated paralytic polio. In the past two years, circulating vaccine-derived poliovirus, or VDPV, has emerged as an even bigger challenge to polio eradication than WPV. VDPV type 2 (VDPV2) is the most prevalent strain. (In countries like the U.S. where only IPV is used, development of VDPV is not a threat.)
Low immunization rates are the genesis of VDPV. Therefore, vaccinating children with OPV is the best way to prevent an outbreak of VDPV from occurring. While it may seem counterintuitive, the OPV vaccine protects children whether the kind of polio is WPV or VDPV. Outbreaks (whether WPV or VDPV) are usually rapidly stopped with 2–3 rounds of high-quality supplementary immunization activities (immunization campaigns).
In addition to these high-quality immunization campaigns, the GPEI is working hard to deploy an improved novel oral polio vaccine type 2, or nOPV2, that contains improvements that help make the vaccine virus less likely to mutate and cause disease in communities with low immunization rates.
Stumbling block no. 2: WPV1 in Africa. In 2015 WPV2 was eradicated. In 2019, WPV3 was declared eradicated leaving only WPV1. Despite the GPEI’s coordinated global efforts, an outbreak of WPV1 infections occurred in Malawi in February of this year. These were the first cases of wild polio detected in Africa in more than five years. This outbreak spurred a UNICEF-supported drive in Malawi and several surrounding countries to vaccinate 9 million children.
Stumbling block no. 3: polio in Ukraine. On October 6, 2021, 19 years after the European region as a whole was declared polio-free, a 17-month-old girl in western Ukraine was stricken with paralytic polio caused by VDPV2. In mid-January 2022, UNICEF announced its support of Ukraine’s plan to stop a polio outbreak. As UNICEF’s Representative in Ukraine said, “Polio anywhere is a threat to children everywhere. Vaccination is the only effective way to protect every child and stop the outbreak.”
In late February 2022, Russia invaded Ukraine. By early March, 22 cases of polio were identified in Ukraine. The reason for the emergence of this outbreak is unclear. We do know, however, that routine childhood vaccination programs were disrupted in many countries due to the COVID-19 pandemic. As the horrific war in Ukraine shows no signs of ending anytime soon, the European Union announced its plan to buy polio and measles vaccines for Ukraine refugees. In addition, several members of the GPEI alliance, for example, the WHO, CDC, and Gates Foundation are likely to join forces in meeting the health challenges of those in Ukraine as well as displaced populations from Ukraine.
Stumbling block no. 4: COVID-19 vaccine concerns spilling over into routine immunizations. WPV infection was eliminated from the U.S. in 1979 and reversion from the oral polio vaccine back to the inactivated polio vaccine in order to prevent vaccine-derived poliovirus infections occurred here in 2000. Therefore, “polio is out of sight and mind” of most Americans. Nonetheless, we should all be concerned by headlines like the one on April 21, 2022 in MedPage Today, “CDC Finds ‘Concerning Dip in Kindergartener Vaccination Coverage’—National rate dropped below public health target of 95%.” It may be a good time for everyone to read the CDC’s website, “Polio Vaccination: What Everyone Should Know.”
Viruses don’t respect international borders. A basic tenet of the global campaign to eradicate polio is that as long as one country has not eliminated the virus, it is important to keep on vaccinating children across the globe. As Dr. Hugo Scornik, a pediatrician and president of the Georgia Chapter of the American Academy of Pediatrics, said, “We just want to keep measles, polio, and all things we vaccinate against out of the political arena.” I agree.