Critical Care Update| Volume 42, ISSUE 1, P5-10, January 2023

Polio Is Back

Published:November 15, 2022DOI:
      New York
      Fadulu L. Polio emergency declared in New York. Minneapolis Star Tribune. September 10, 2022.
      Larkin H. What all physicians need to know about the polio resurgence in New York State.JAMA. 2022;328:1020-1022.
      A disease reminiscent of early life for my generation (ie, baby boomers [born 1946-1964]) returned to the news when the governor of New York declared a state of emergency over a growing polio outbreak in an effort to better equip health care providers with tools to curb the spread of a sometimes disabling virus before further impact on this state was identified. The order by the governor allowed emergency service workers, midwives, and pharmacists to administer a polio vaccine. The declaration also required health care providers to send immunization data to New York health officials so that they could determine where to target vaccination efforts. The first polio case in nearly a decade was identified in July 2022 in New York State. Officials reported that an unvaccinated man was infected by a virus that had been shed from the recipient of an oral polio vaccine, which had not been administered in the United States since 2000. The oral vaccine was thought to be safe but contained small amounts of weakened live virus that could circulate and strengthen if communities were undervaccinated. At the time of this report, no other cases had been identified by the state, but officials have been monitoring wastewater for polio, which is typically found in the fecal matter of an infected person, to track whether the virus was spreading. New York City officials stated that they had identified polio in the city's wastewater in August 2022. Polio had also been identified in multiple samples of wastewater from downstate counties in New York between May and August. Polio vaccination rates in counties where samples of wastewater containing polio were collected were lower than those in the remainder of New York State. Vaccination rates in the affected rural counties ranged from 59% up to 79%. State officials indicated that they wanted to see the polio vaccination rate rise above 90%.
      The New York case of polio described was caused by a vaccine-derived poliovirus. The patient was unvaccinated and had not traveled to a country where polio is a significant risk. Genomic sequencing suggests that the virus had been circulating locally undetected for as much as a year according to data from the Centers for Disease Control and Prevention (CDC). Infection with poliovirus, an enterovirus that primarily infects the intestinal tract, is symptomatic only about 25% of the time, typically causing a flulike illness. Depending on the virus type, 1% to 5% of people with infections will also develop meningitis. About 0.5% to 0.05% of individuals who are infected will develop paralysis after the virus infects the spinal cord, and a small proportion of these individuals will die because of respiratory failure according to the CDC.
      A review of recent cases points out that paralytic polio is a red flag suggesting that there could be 100 people or more in the community who were not showing symptoms. A genetically similar poliovirus has been detected in several wastewater samples from counties near the location of the index case in New York. Polio has also been identified in New York City sewage, supporting evidence of community circulation of the virus. State officials indicate that the detection of poliovirus in wastewater samples in New York City is alarming but not surprising. State officials were also not surprised that the paralytic case of polio occurred in an unvaccinated individual living in an area with a low polio vaccination rate. State officials also warned that poliovirus could spread rapidly in a small, consolidated group of individuals in the presence of a significant percentage of unvaccinated people. Another concern raised by New York health officials is that in this state with multiple ethnicities, every group has pockets of unvaccinated people. In general, only unvaccinated or incompletely vaccinated individuals are at risk for symptomatic polio. Because there are no antiviral or other treatments for polio, vaccination is the key to preventing disease. State officials recommended immediate reporting to public health agencies if polio is suspected. A CDC protocol is now available to submit suspected samples for further evaluation.
      Diagnosing infection from poliovirus is complicated because many patients who are infected never develop symptoms. Individuals with infection generally have nonspecific viral symptoms including fever, sore throat, fatigue, headache, nausea, and abdominal pain. Clinical screening involves testing stool or samples from the oropharynx for enterovirus. Confirming poliovirus infection involves collecting stool samples over 2 days for evaluation by public health departments or the CDC. Unfortunately, this evaluation is complicated, expensive, and impractical in many cases for a disease that is quite rare. Screening some patients with nonspecific viral symptoms may be justified in areas with known community spread of poliovirus. The Department of Health recommends screening for unvaccinated patients with at least 2 symptoms, including fever or sore throat, who are living in areas where polio is present. Patients with meningitis in these areas should also be screened.
      More specific to poliovirus infection is weakness in the limbs progressing over several days called acute flaccid paralysis. These findings are usually, but not always, worse on one side of the body and progress from proximal to distal muscles. Muscle strength and tone are affected, and reflexes are decreased. Sensation is not affected. Difficulty with speaking or swallowing as well as respiratory distress may also occur. These symptoms suggest anterior myelitis.
      Acute flaccid paralysis is more often associated with other diseases including other enteroviruses, adenoviruses, West Nile virus, Guillain-Barré syndrome, and botulism according to the CDC. Other factors that should trigger the consideration of polio include polio disease in the area, unvaccinated or incomplete vaccination of the population, travel to or exposure to people from countries with high polio risk, and contact with someone who is infected.
      Minor P. The polio endgame. Hum Vaccin Immunother. 2014;10:2106-2108.
      Donaldson LJ, Hayes K, Heyman D. Eradicating polio: the sprint at the end of the marathon. BMJ. 2018;361:k2077.
      Bahl S, Bhatnagar P, Sutter RW, Roesel S, Saffron M. Global polio eradication - way ahead. Indian J Pediatr. 2018;85(2):124-131.
      Center for Preparedness and Response. Polio disease and poliovirus. Accessed July 12, 2022.
      As Philip Minor from the National Institute for Biological Standards and Control in the United Kingdom points out in his review, global polio eradication is the largest public health intervention aimed at a single infectious disease in history. At the turn of the century, early programs had reduced the number of countries with serious endemic polio to India, Pakistan, Afghanistan, and Nigeria. Additional progress in these areas appears slow. One hopeful sign at the turn of the century is progress toward eradication of polio from India.
      Minor divides the history of worldwide polio into 4 periods. Funeral art from the Middle Kingdom of Egypt from 1400 bc shows lower extremity changes consistent with polio. Despite a striking clinical presentation, there are fewer than a dozen instances identifiable in the medical literature until the end of the 19th century. Commentators suggest that there was little disease until a second phase combined with an improved standard of living and hygiene when polio began to occur in pronounced epidemics in Western countries, from 1900-1960. In the United Kingdom, the peak period of polio presentation was the 1950s, after which the “inactivated, killed,” polio vaccine developed by Salk and later the live attenuated vaccine as an oral preparation from Sabin eliminated polio as an acute public health problem. However, polio still occurred at high frequency in developing countries despite large amounts of vaccine being used, and for some time it was thought that oral polio vaccine, in particular, did not work in tropical climates. The third phase of the fight against polio came to an end in the mid-1980s when polio incidence was falling in South American countries. Improved outcomes in South America were accomplished by mass administration of the oral polio vaccine of Sabin. Large amounts of oral vaccine were given in immunization campaigns executed over a short period of time so that susceptible polio was reduced suddenly, and transmission of the virus was interrupted. During these periods of mass immunization, India regularly treated over 120 million children in a single day and repeated the exercise many times throughout the year. Developed countries used a routine administration strategy in which children were vaccinated at a set age rather than all at once as a single cohort. Investigators noted that in temperate climates, polio transmission occurred during the summer so that winter immunization was eventually able to reduce the pool of vulnerable individuals to a level sufficiently small to interrupt polio circulation. Where exposure to polio occurred on a year-round basis, as in tropical climates, the impact of this routine vaccination strategy on the size of the susceptible pool of virus was insufficient to interrupt transmission so that massive vaccination programs were required. The fourth and final phase of the history of polio is the discontinuation of oral vaccination after the eradication of infectious polio. The discontinuation of oral vaccination against polio should eliminate the risk of vaccine-dependent polio in patients treated with the oral preparation. Unfortunately, this has not been a trivial exercise.
      Early data on the pathogenesis of polio come from 1909 when polio was shown to be caused by a virus described as a species C enterovirus, a group including many of the Coxsackievirus A strains, within which the polio genome can be active in recombination. Recombination likely has epidemiologic significance in generating virus with novel properties or removing regions of the viral genome that handicap viral growth or transmission. Enteroviruses, which include polio, grow mainly in the gut where infection is entirely asymptomatic. Sometimes the virus may spread to somatic tissues where it may replicate and spread further to other regions including the airway, the regional nervous system, and the central nervous system. In the central nervous system, polio specifically targets and destroys motor neurons, leading to the classic clinical presentation of withered extremities. Typically, the lower limbs are affected hemilaterally, but infection further up the spinal cord may affect respiratory centers, leading to bulbar polio where the victim will die without assisted respiration.
      Although paralytic poliomyelitis attracts significant clinical attention, it is very rare, occurring in an estimated 1% or fewer of infections. Most infection is confined to the gut and is spread from there through a viremic phase. If the infected individual has circulating humoral antibodies, disease is less likely to occur. This is the reported reason for the development of polio epidemics at the same time as improvements in hygiene standards. Infants exposed to human waste and poliovirus early in life would be protected by maternal antibodies. Only when exposure to the virus occurs later in life does spread from the gut to other sites occur. The protective effect of humoral antibodies was demonstrated in the 1950s.
      The pathogenesis of polio means that most infections are silent; counting cases is only an indirect measure of the presence of the virus. For eradication programs, this means that if one country in the world has circulating polio, the entire world is at risk because polio may be exported by asymptomatic individuals who are impossible to identify easily. A dramatic example occurred in Nigeria in 2002. Immunization in Northern Nigeria was stopped because a local belief arose that the polio campaign was harmful and could result in the sterilization of children. Ultimately, the virus spread from Nigeria to neighboring countries over a period of months, and the whole of central Africa became reinfected. In addition, travelers from Nigeria carried the virus to Yemen and Indonesia. Export of the virus from endemic countries including India has been repeatedly documented since this time.
      Another factor in polio eradication is the various types of viruses. There has been silent circulation of a type 1 poliovirus strain in Israel detected by the surveillance of sewage. This virus strain has unusual antigen properties and originated in Pakistan. This is a concern because it appears that type 1 polio is identified in areas of good and poor hygiene, and vaccine coverage in Israel using inactivated polio vaccines was well over 90% at the time of the polio spread in that country. Silent circulation of the virus was also identified in Egypt. Unfortunately, these data suggest that inactivated polio vaccines cannot be relied on to interrupt transmission consistently. Oral polio vaccination involves the introduction of a live attenuated virus. Not all jurisdictions are willing to use this approach. Another concern for eradication programs is undetected circulation of the virus. In some eradication programs, surveillance has focused on cases with acute flaccid paralysis. Thus, silent transmission of polio would not be detected. Surveillance of sewage is becoming more important in the United States, the Middle East, and Western Europe.
      Polio may occur in 3 types (types 1, 2, and 3), with the current clinical activity associated mainly with type 1. Minor reports no case of type 2 poliovirus since 2015 and no case of type 3 poliomyelitis since 2019. Despite no recent activity from type 2 polio, it is included in vaccine formulations. Minor suggests that for all types of polio given as an oral vaccine, virus replication in the gut may lead to more virulent evolution of the virus, which can cause paralytic poliomyelitis. Thus, paralytic poliomyelitis may be caused by vaccines administered to limit the spread of the virus. Additional epidemiology studies suggest that with replication in the gut, polio that gained access to the patient via immunization or natural means (fecal-oral spread) may also regain or enhance transmissibility.
      A recent summary from the CDC suggests that only active type 1 wild poliovirus now remains. Vaccination strategies include oral polio vaccine and inactivated poliovirus vaccine. Oral polio vaccine is used in many countries to protect against polio and has been essential to polio eradication. There are different types of oral polio vaccine that may contain 1, a combination of 2, or all 3 different types of attenuated, or weakened, virus. Each vaccine strategy has advantages and disadvantages. After wild poliovirus type 2 was declared eradicated in 2015, the world has moved from trivalent to bivalent oral polio vaccine. Trivalent oral polio vaccine contains all 3 types of poliovirus, whereas the bivalent oral polio vaccine contains only poliovirus types 1 and 3. Thus, protection against wild poliovirus type 2 is not offered in current oral vaccine preparations.
      Inactivated poliovirus vaccine protects against all 3 types of polioviruses. Inactivated poliovirus vaccine does not contain live virus, so people receiving this vaccine do not shed the virus and cannot infect others. This vaccine cannot cause disease. Inactivated poliovirus vaccine does not stop transmission of the poliovirus. Oral poliovirus vaccine is used when a polio outbreak must be contained, even in countries that typically rely on inactivated poliovirus vaccine for routine immunization. In general, once polio has been eradicated in areas of concern, the use of oral polio vaccine is stopped to prevent resumption of transmission, which may be caused by vaccine-dependent poliovirus. In countries that have used bivalent oral polio vaccine, a single dose of inactivated polio vaccine may be added to protect against wild poliovirus type 2.
      Public Health data from London reveal a reduction of the number of children with polio paralysis from 1,000 per day in 1988 to 22 in total in 2017. However, in more recent years, deadlines for interrupting the transmission of polio have been repeatedly missed or modified. Staff providing the vaccine have been intimidated or murdered, and morale has fallen significantly. One obvious explanation is that the vast majority of polio is invisible. Only 1% of children who become infected are paralyzed. Other factors causing delays in progress with polio eradication are specific to each geographic area. Insecurity is a dominant factor. Political divides, or in some cases terrorist groups, isolate children from immunization programs. For example, the Taliban limits the access of vaccine providers to communities in need. Population movement within and across countries with endemic polio sustains poliovirus circulation. Constant work on social mobilization is needed at the local level to combat vaccine refusal and sustain public confidence in vaccination. Stopping the transmission of poliovirus globally depends on an appropriate balance of leadership; commitment; and action at the global, national, regional, and local level. Political alignment, supportive communities, excellent program delivery, and commitment to solve these intractable problems are essential. Among countries seeking polio eradication, India continues to be at the point of attempts to become a polio-free country.
      Certifying the eradication of polio is an independent and rigorous process. Wild poliovirus must be demonstrated to be absent from the world for 3 or more years. Polio must not be found in suspected cases, healthy people, or the environment, all requiring a high degree of surveillance. With polio recently identified in New York, it appears impossible that the celebration of polio eradication can take place before 2025.
      Even after interrupting the transmission of the virus, technical, logistical, managerial, and financial challenges remain to sustain a polio-free world. Current goals of the World Health Organization (WHO) are the detection of remaining poliovirus wherever it is, replacing oral polio vaccine with a vaccine that cannot mutate to cause paralysis, and making sure that poliovirus kept in laboratories and vaccine manufacturing sites cannot escape.
      The most recent timeline for polio eradication, extending beyond the midportion of this decade, began in 1988 with a target date at the end of the year 2000 for the first phase. The focus in this initial phase was global vaccination, strategy development, resource mobilization, and rapid intervention. By the year 2000, the number of countries with endemic polio was 20 compared with over 125 in 1988. Paralytic poliomyelitis cases decreased by greater than 99% from greater than 350,000 estimated cases in 1988 to 2,849 reported cases in the year 2000. The second phase of polio eradication began in 2001 and ended shortly after 2010. The focus of this work was countries with major difficulty in accessing marginal populations where effective immunization was difficult. The third phase of this Global Polio Eradication Initiative targeted polio present in India. Evidence suggesting successful polio eradication in India reduced the list of countries with major risk of endemic polio to Pakistan, Afghanistan, and Nigeria. Politics and risks imposed by terrorist networks complicated work in these sites. Final steps in polio eradication included the removal of Sabin poliovirus type 2 from the oral poliovirus vaccine. This intervention was implemented in 2016 after evidence of wild type 2 poliovirus eradication was gathered. Withdrawal of this oral poliovirus vaccine after wild type 2 poliovirus eradication was the largest recall of a medicinal product ever attempted. Over 150 countries participated. A new vaccine supply featuring type 1 and type 3 Sabin poliovirus was introduced with the inclusion of inactivated poliovirus vaccine to maintain immunity against poliovirus type 2. Unfortunately, the emergence and possible circulation of vaccine-derived poliovirus type 2 are concerns in the presence of decreasing mucosal immunity against type 2 poliovirus. Another concern was inadequate vaccine stocks leading to an irregular pattern of medication administration.
      The road to polio eradication continues to be laborious and complex. Investigative bodies report that wild poliovirus type 2 was last detected in Northern India in 1999, and the world was certified free of wild poliovirus type 2 in 2015. This allowed the removal of Sabin type 2 virus from oral poliovirus vaccines. Wild poliovirus type 3 was last detected in Nigeria in 2012. At this point, only wild poliovirus type 1 continues to circulate in Nigeria, Afghanistan, and Pakistan. Unfortunately, these areas, likely polio reservoirs, are difficult to access because of security concerns. A second issue is the “zoo” of vaccine-related polioviruses and immunodeficiency-associated vaccine-dependent poliovirus disease. A significant remaining challenge to the global community is the lack of consistent polio eradication when individuals continue to be paralyzed by vaccine-related polioviruses. The problem of vaccine-related disease is further complicated by the genetic evolution of polioviruses, which could easily lead to re-establishment of endemic and epidemic transmission of disease. To address the zoo, including the type 2 virus, aggressive surveillance work is necessary, particularly in immunodeficient populations, to determine whether any of these individuals are excreting poliovirus. Antiviral agents will need refinement to eliminate viral replication and excretion from immunodeficient individuals.
      Global certification of the eradication of polio requires as a minimum 3 years after the last detection of wild poliovirus globally in conditions of high-quality surveillance. Review of the evidence will rely on National Certification Committees reporting to Regional Certification Commissions with subsequent reports to the Global Certification Commission for final review. For example, regional certification of polio eradication was successfully concluded in the Americas in 1994 and in the Western Pacific in 2000, with documented certification in the European region in 2004. Africa and Eastern Mediterranean regions are still under surveillance conditions. Global certification of polio eradication is currently defined as 3 years from the last detection of polio to achieve certification of a disease-free state. Because polio can exist for extended periods of time in vivo, chronic poliovirus excreters could present a serious threat to eradication. These individuals could cause re-established poliovirus transmission. A single-drug regimen is under investigation to provide therapy for prolonged or chronic polio excreters. However, to prevent the development of resistance, a second drug for polio is required. The discontinuation of Sabin virus therapy for type 1 and type 3 polio would require worldwide coordination. Another critical factor is that vaccine production to manage polio with all current vaccines requires the growth of live poliovirus. Thus, many laboratories and production facilities will need to continue to work with poliovirus products for the foreseeable future. In addition, chronic polio infection with replication and excretion has been demonstrated in individuals for more than 30 years. Thus, vaccination to induce immunity against poliovirus needs to continue. The steps needed to maintain the necessary immunity base against polio are still under discussion.
      If we assume that polio has not been detected within the 3-year window, 4 goals have been identified as a postcertification strategy. The first goal is the containment of polio sources from laboratories and production sites. A second goal is the discontinuation of oral poliovirus vaccine use. A second part of this second arm is surveillance and management of poliovirus released by chronic excreters. Third among the goals stated in the Global Polio Eradication Initiative is the removal of bivalent oral polio vaccine and maintenance of population immunity through alternative routine immunization efforts. The final goal is comprehensive, compulsive, and effective monitoring to provide the necessary surveillance to document polio eradication.
      O'Leary A. Overcoming challenges en route to polio eradication. Lancet. 2022;400:1191.
      Sáinz MP, Pelayo R, Laxe S, Castaño B, Capdevilla E, Portell E. Describing post-polio syndrome. Neurologia (Engl Ed). 2022;37:346-354.
      The Lancet. Polio eradication: falling at the final hurdle? Lancet. 2022;400:1079.
      Recent years have seen significant developments in polio eradication. In 2019, global eradication of type 3 poliovirus was declared. In 2020, Africa was classified as free of endemic polio. Wild poliovirus had been confined to pockets in Afghanistan and Pakistan. Unfortunately, polio has since returned to many parts of the world, necessitating the identification of funding for eradication in the setting of global economic difficulty and geopolitical crises.
      Coronavirus disease 2019 (COVID-19) temporarily halted the Global Polio Eradication Initiative immunization campaigns, putting over 80 million children at risk. Consequently, outbreaks of circulating vaccine-derived poliovirus tripled from 2019 to 2020 with over 1,100 children suffering paralysis. Paralysis caused by wild polio has since been identified in Africa as well. Circulating vaccine-derived poliovirus has been detected in wastewater in the United States, the United Kingdom, and Israel, although rapid vaccination campaigns should prevent this from becoming an immediate risk to public health. Nigeria has identified a large outbreak of vaccine-dependent polio, and high risk is identified for additional outbreaks in Brazil, the Dominican Republic, Haiti, and Peru. In part, this is due to reduced vaccination rates. Ongoing funding for polio eradication is a major concern. The Global Polio Eradication Initiative needs funding to eradicate polio by 2026. A major component of this initiative is vaccination of over 300 million children annually and continued surveillance for polio in 50 countries. It remains unclear whether these financial objectives can be met.
      Novel polio vaccines, now under development, should help control outbreaks of circulating vaccine-derived poliovirus and reduce the risk of new cases. A novel oral polio type 2 vaccine using a more genetically stable virus has received emergency authorization by the WHO. Performance data on new vaccines are being collected. Unfortunately, novel vaccines have been in short supply, and technical solutions may not be enough to overcome barriers to polio eradication.
      What is the major goal? Authorities debate whether polio should be eradicated as a disease rather than as a virus to be eliminated; others have urged the sustained control of polio cases. The Global Polio Eradication Initiative continues to have a target of polio elimination from 2022 through 2026. In fact, this program has made significant progress. Since 1988, a 99.9% reduction in the global incidence of polio has been observed, and more than 1.5 million lives have been saved with avoidance of polio-related paralysis in 16 million people. Types 2 and 3 wild poliovirus have been eradicated worldwide. Despite this, the initiative must confront the challenges summarized previously that threaten the success of the program.
      In addition to social and economic concerns, polio itself has changed. Until relatively recently, polio was considered a neurologically stable disease that could leave functional sequelae after the acute phase. However, in the 1970s, cases were detected with new symptoms causing functional worsening in patients with a history of poliomyelitis. These patients were said to have postpolio syndrome (PPS).
      A number of criteria have been described for this problem. Prior paralytic poliomyelitis with evidence of motor neuron loss is an important part of the history in patients with PPS. These individuals have a period of partial or complete functional recovery after the acute phase followed by an interval, usually 15 years or more, of stable neurologic function. Unfortunately, this is followed by gradual or sudden onset of progressive and persistent new muscle weakness or abnormal muscle fatigability with or without generalized fatigue, muscle atrophy, or muscle and joint pain. Less commonly symptoms associated with PPS include new problems with breathing or swallowing. Symptoms typically persist for at least 1 year. Other neurologic, medical, or orthopedic problems must be excluded as a cause of new symptoms.
      The pathogenesis of PPS is unclear. One major hypothesis suggests decompensation between chronic denervation and reinnervation mechanisms that help maintain muscle function. Another possibility is the reactivation of latent virus in motor neurons. Although risk factors for PPS are not well characterized, investigators suggest that the risk for developing this syndrome may increase with older age, female sex, greater severity of motor symptoms in acute poliomyelitis, lower level of functional recovery after acute infection, and longer duration of the latent phase. Other findings suggesting PPS risk include the use of mechanical ventilation in the acute phase and a high level of physical activity.
      The mean age of primary infection in 1 large series is approximately 2 years; in other developed countries, it is usually seen in older patients. The severity of acute infection is evaluated with different methods including demographic factors such as the severity of sequelae after recovery from primary infection, need for mechanical ventilation, number of limbs affected by the primary polio infection, time needed for gait recovery, and number of interventions. Older age at disease onset may be associated with more severe acute infection, leading to more severe sequelae. All these factors increase the risk of developing PPS. The most frequent symptom of PPS was musculoskeletal pain followed by fatigue. Loss of strength was reported by 40% of patients. Nine percent of the affected individuals reported cognitive problems. Dysphagia was reported in approximately 12% of patients. Videofluoroscopy was generally unremarkable in these individuals. Women were significantly more likely to present with fatigue than men. Loss of strength was reported by 39% of patients. When patients reported loss of strength, an electromyographic abnormality was more likely. Perhaps the greatest issue in the identification and management of PPS is the high frequency of subjective symptoms. Additional data are needed.
      What's Next?
      Gostin LO. Living in an age of pandemics-from COVID-19 to monkeypox, polio, and Disease X. JAMA Health Forum. 2022;3:e224062.
      The WHO has declared COVID-19, monkeypox, and polio public health emergencies of international concern. The United States has been added to the list of poliovirus outbreak countries. Despite the diversity of these pathogens, similar social and global forces have propelled these 3 diseases, with a massive impact on health and society. Several recurring lessons can be found.
      Zoonotic agents including human immunodeficiency virus, severe acute respiratory syndrome, Ebola, monkeypox, and COVID-19 account for 60% of all communicable diseases and 70% of novel diseases. Zoonotic spillovers are more frequent and result in outbreaks spreading more rapidly due to human behavior. As man encroaches on wildlife environments at an alarming rate for agriculture, resource extraction, and urban development, ecosystems are destroyed, and wild species are displaced and placed under stress. The mingling of wildlife, humans, and livestock increases zoonotic spillovers because international trafficking by animal life creates increasing risk. For example, species that harbor pathogens migrate to cooler climates, potentially across continents. Climate change also expands vectors for pathogen spread to new geographic areas as in mosquitoborne diseases. Urbanization increases human population density, driving person-to-person spread of pathogens and rapid transportation with mass migration, which propel global disease outbreaks throughout the world. At present, 56% of the world population lives in cities. This percentage will only continue to increase.
      The WHO has identified several areas of shortcomings that must be addressed. First is the need to rebuild core global health system capacities such as surveillance, laboratory support, human resources, and risk communication. For example, a great need for medical masks and medical gloves has left health care workers dangerously ill-equipped to provide bedside care. This challenge is greater in low-income countries. A second need is global cooperation with data sharing. This issue was typified by the controversy over origins of COVID-19. With an interdependent global health care system, sharing of diagnostic tools, personal protective equipment, vaccines, and other therapies is essential. Countries that are inadequately equipped will become reservoirs of disease. International communication will facilitate adequate and appropriate sharing of resources. A final major need is effective international vaccination programs. For example, recent data suggest that 25 million children missed adequate COVID-19 vaccination.
      Finally, the WHO identified several areas requiring immediate action. First is recognition that epidemics begin with spillover of zoonotic pathogens between geographic areas and related populations. Protection of the environment and related human and animal populations is essential to control the spread of disease. Adequate surveillance will identify high-risk pathogens, allowing rapid deployment of necessary resources for outbreaks. Stockpiles of needed supplies must be shared globally. International health systems improve the response to disease. Periods between pandemics allow building capacity and creating platforms to respond to high-priority pathogens as they appear. Finally, education systems must train additional caregivers and help prevent the growth of poverty in affected populations. A strong education system will prevent loss of years of life expectancy and educational skills. The WHO would argue that we are now at a turning point in the evolution of global health. Will we prepare?
      Summary Points
      • Polio returned to the public health consciousness in the United States when the first case in nearly a decade was identified in July 2022 in New York State. The patient was unvaccinated and received the virus that had been shed from an individual who received an oral polio vaccine, which had not been administered in the United States in decades. A common surveillance technique to identify polio in populations is the evaluation for the virus in sewage and other wastewater. Because polio is transmitted using a fecal-oral route, the evaluation of sewage is an appropriate screening technique. Multiple sites with sewage positive for polio were identified in New York. Vaccination rates in underserved areas of the state were less than 60% compared with a goal of 90% vaccination against polio.
      • A case of symptomatic polio suggests that there could be 100 infected people or more in the community without symptoms. Because there is no specific antiviral treatment for polio, vaccination is the key to prevention. When symptoms appear, nonspecific viral symptoms including fever, sore throat, fatigue, headache, nausea, and abdominal pain may be found. More specific polio findings are weakness in the limbs progressing over days creating acute flaccid paralysis. Muscle strength and tone are affected, and reflexes are decreased. Sensation is not altered. Respiratory distress may occur and can progress to a life-threatening problem.
      • The history of polio dates back to biblical times. Contemporary experience with polio dates to the beginning of the 20th century. A series of massive vaccination programs have led to episodic interruption of the spread of polio. Unfortunately, vaccination can also contribute to the evolution of the virus and, thus far, has not provided a definitive answer to the spread of polio. Polio may occur in 3 types (types 1, 2, and 3) with clinical activity associated with different types of polio at different times. For example, no case of type 2 polio has been identified since 2015.
      • Polio continues to be present in countries with a limited public health infrastructure. Polio has recently been identified in Nigeria, Afghanistan, Pakistan, and episodically in India. These countries, which are likely polio reservoirs, are difficult to access because of security concerns that affect the use of health care workers. COVID-19 also limited the access of health care workers to the population and the ability of these health care workers to effectively maintain vaccination programs.
      • Classic paralytic poliomyelitis is associated with spinal cord injury followed by motor neuron function loss. A new symptom complex recently associated with polio is PPS. Patients with this syndrome have prior paralytic poliomyelitis with evidence of motor neuron injury. PPS victims have a period of partial or complete functional recovery followed by an interval, which could be years, of stable neurologic function. Unfortunately, this period of stability is followed by gradual or sudden onset of progressive and persistent new muscle weakness, fatigability, muscle atrophy, and joint pain. PPS symptoms typically persist for at least 1 year. The pathogenesis of PPS remains unclear.
      • To permit polio eradication, which is thought to be the major public health challenge in the world today, several contemporary problems must be addressed. Among these is the need to build a global health system with capacity for sharing of surveillance information, laboratory support, human resources, and risk communication. Inadequate supplies of personal protective equipment are unacceptable when millions require vaccination. Sharing of diagnostic tools, vaccines, and other therapeutics is essential. These resources cannot be limited to countries with robust economies. Finally, because vaccination is essential to polio control, adequate and equal international vaccination programs are needed. For example, recent data suggest that 25 million children missed adequate COVID-19 vaccination.


      The author acknowledges Ms Sherry Willett for expert preparation of this series for Air Medical Journal.
      David J. Dries, MSE, MD, is a senior fellow at HealthPartners Institute and a professor of surgery, an adjunct clinical professor of emergency medicine, and the John F. Perry, Jr, chair of surgery at the University of Minnesota in St Paul, MN, and can be reached at [email protected]