Cases Of Wild Poliovirus Type Research Articles

Threat of resurgence or hope for global eradication of poliovirus?

Recent outbreaks of poliomyelitis in countries that have been free of cases for decades highlight the challenges of eradicating polio in a globalized interconnected world beset with a novel viral pandemic. We provide an epidemiological update, advancements in vaccines, and amendments in public health strategy of poliomyelitis in this review. Last year, new cases of wild poliovirus type 1 (WPV1) were documented in regions previously documented to have eradicated WPV1 and reports of circulating vaccine-derived poliovirus type 2 (cVDPV2) and 3 (cVDPV3) in New York and Jerusalem made international headlines. Sequencing of wastewater samples from environmental surveillance revealed that the WPV1 strains were related to WPV1 lineages from endemic countries and the cVDPV2 strains from New York and Jerusalem were not only related to each other but also to environmental isolates found in London. The evidence of importation of WPV1 cases from endemic countries, and global transmission of cVDPVs justifies renewed efforts in routine vaccination programs and outbreak control measures that were interrupted by the COVID-19 pandemic. After the novel oral poliovirus vaccine type 2 (nOPV2) received emergency authorization for containment of cVDPV2 outbreaks in 2021, subsequent reduced incidence, transmission rates, and vaccine adverse events, alongside increased genetic stability of viral isolates substantiates the safety and efficacy of nOPV2. The nOPV1 and nOPV3 vaccines, against type 1 and 3 cVDPVs, and measures to increase accessibility and efficacy of inactivated poliovirus vaccine (IPV) are in development. A revised strategy utilizing more genetically stable vaccine formulations, with uninterrupted vaccination programs and continued active surveillance optimizes the prospect of global poliomyelitis eradication.

Progress Toward Poliomyelitis Eradication - Afghanistan, January 2018-May 2019.

Since October 2016, Afghanistan and Pakistan have been the only countries with reported cases of wild poliovirus type 1 (WPV1) (1). In Afghanistan, although the number of cases had declined during 2013-2016, the polio eradication program experienced challenges during 2017-2019. This report describes polio eradication activities and progress in Afghanistan during January 2018-May 2019 and updates previous reports (2,3). During May-December 2018, insurgent groups (antigovernment elements) banned house-to-house vaccination in most southern and southeastern provinces, leaving approximately 1 million children inaccessible to oral poliovirus vaccine (OPV) administration. During January-April 2019, vaccination targeting children at designated community sites (site-to-site vaccination) was permitted; however, at the end of April 2019, vaccination campaigns were banned nationally. During 2018, a total of 21 WPV1 cases were reported in Afghanistan, compared with 14 during 2017. During January-May 2019, 10 WPV1 cases were reported (as of May 31), compared with eight during January-May 2018. Sewage sample-testing takes place at 20 sites in the highest-risk areas for poliovirus circulation; 17 have detected WPV1 since January 2017, primarily in the southern and eastern provinces. Continued discussion with antigovernment elements to resume house-to-house campaigns is important to achieving polio eradication in Afghanistan. To increase community support for vaccination, collaboration among humanitarian service agencies to address other urgent health and basic needs is critical.

Progress Toward Polio Eradication - Worldwide, 2015-2016.

In 1988, the World Health Assembly resolved to eradicate poliomyelitis. Wild poliovirus (WPV) transmission persists in only two countries (Afghanistan and Pakistan) after the removal of Nigeria from the list of countries with endemic polio in September 2015.* Indigenous WPV type 2 has not been detected since 1999 and was declared eradicated by the Global Commission for the Certification of Poliomyelitis Eradication in September 2015.(†) Since November 2012, when the last case of WPV type 3 was detected in Nigeria, WPV type 1 has been the sole circulating type of WPV (1). This report summarizes global progress toward polio eradication during 2015-2016 and updates previous reports (2). In 2015, 74 WPV cases were reported in two countries (Afghanistan and Pakistan), a decrease of 79% from the 359 WPV cases reported in 2014 in nine countries; 12 WPV cases have been reported in 2016 (to date), compared with 23 during the same period in 2015 (3). Paralytic polio caused by circulating vaccine-derived poliovirus (cVDPV) remains a risk in areas with low oral poliovirus vaccine (OPV) coverage. Seven countries, including Pakistan, reported 32 cVDPV cases in 2015 (4). In four of these countries, ≥6 months have passed since the most recent case or isolate. One country (Laos) with VDPV transmission in 2015 has reported three additional cVDPV cases in 2016 to date. Encouraging progress toward polio eradication has been made over the last year; however, interruption of WPV transmission will require focus on reaching and vaccinating every missed child through high quality supplementary immunization activities (SIAs) and cross-border coordination between Afghanistan and Pakistan (5,6).

Public Health Innovations on the Way to Interruption of Poliovirus Transmission in Nigeria.

The polio eradication journey in Nigeria has been long, with a mix of good and not so good news over the years. Nigeria was very close to interrupting transmission of polio and then experienced an upsurge of transmission, owing to an interaction of several factors. At one point, Nigeria became a net exporter of poliovirus to polio-free countries, but at the end of 2013 there was clear evidence that the hard work and numerous innovations that the government and its partners had implemented were beginning to pay off: the number of cases of wild poliovirus (WPV) type 1 infection had decreased by 58%, compared with 2012; there had not been any cases of WPV type 3 infection detected since November 2012; and there had also been a reduction in the genetic diversity (clusters) of WPV1, from 8 in 2012 to 2 in 2013. In 2014, there were 6 cases of WPV1 infection, compared with 53 in 2013, and the number of genetic clusters had decreased to 1. Poliovirus transmission in Nigeria has been driven by reservoirs in northern Nigeria, where several states are considered to be at very high risk of poliovirus transmission. Additionally, 3 states in the northeast region have suffered from insecurity, and this added another facet to the struggle to control polio; several health workers gave the ultimate sacrifice to polio eradication, when they were killed as they conducted their work. All public health programs rely on effective surveillance and prompt response guided by the best information available. Polio eradication, like other infectious diseases surveillance and response programs, relies on prompt detection, registration, and laboratory and epidemiologic confirmation of suspected polio cases; reporting, analysis, use, and feedback of data; and preparedness and response (eg, outbreak investigations, contact tracing, and public health interventions). Like other programs, polio eradication needs managerial and support functions, which include coordination, supervision or performance evaluation, training, and resource provision for infrastructure, including communication. In Nigeria, each of these core activities and support functions were needed for the polio eradication program to produce the remarkable results that it has achieved, given the situation that it is in. New innovations also had to be tried and perfected to solve complex problems that revolved around the community accepting incessant rounds of oral polio vaccination. This supplement presents some of the public health programmatic innovations that the Nigerian government and its polio partners, with the support of the World Health Organization, tried and implemented to interrupt the transmission of polio. The programmatic interventions that are described here include efforts to create demand for polio vaccination; strategies to detect every case of suspected WPV, including those in the environment; methods to determine the underlying population immunity; strategies to effectively plan for, implement, and track vaccination activities, using the latest technologies; and approaches to widen the polio partnership in noncompliant and security-compromised communities. These interventions were enabled by a focused effort to obtain the necessary resources, use them effectively and transparently, provide the needed public health workforce, and ensure accountability for results. In 2014, Nigeria was one of the countries that was affected by the Ebola virus disease outbreak in West Africa. This supplement reviews how the polio partnership demonstrated remarkable flexibility by addressing and quickly overcoming this major public health challenge, using lessons and experiences obtained from polio eradication without compromising the gains that had been won for polio eradication. At the time this supplement was prepared, Nigeria had gone 12 months with no report of WPV and had started using inactivated polio vaccine. We believe that these public health interventions and other activities will help Nigeria enter a poliovirus-free environment. We also believe that these lessons can be adapted to improve routine immunization in Nigeria. We hope you will enjoy learning about these interventions.

Progress Toward Poliomyelitis Eradication--Pakistan, January 2014-September 2015.

Since Nigeria reported its last case of wild poliovirus type 1 (WPV1) in July 2014, Pakistan and Afghanistan remain the only two countries where WPV transmission has never been interrupted. This report describes actions taken and progress achieved toward polio eradication in Pakistan during January 2014-September 2015 and updates previous reports. A total of 38 WPV1 cases were reported in Pakistan during January-September 2015, compared with 243 during the same period in 2014 (an 84% decline). Among WPV1 cases reported in 2015, 32 (84%) occurred in children aged <36 months, nine (32%) of whom had never received oral poliovirus vaccine (OPV). Twenty-six (68%) of the 38 reported cases occurred in the Federally Administered Tribal Areas (FATA) and Khyber Pakhtunkhwa (KPK) Province. During January-September 2015, WPV1 was detected in 20% (64 of 325) of environmental samples collected, compared with 34% (98 of 294) of samples collected during the same period in 2014. The quality and scope of polio eradication activities improved considerably following the establishment of a national Emergency Operations Center, which coordinated polio eradication partners' activities. All activities are following a National Polio Eradication Emergency Action Plan that includes a rigorous action plan for the polio low transmission season (January-April). The presence of WPV1 in environmental samples in areas where no polio cases are detected highlights the need to improve surveillance for acute flaccid paralysis (AFP). Focused efforts to close remaining immunity gaps by locating, tracking, and vaccinating continually missed children and improving coverage with OPV through the routine vaccination program are needed to stop WPV transmission in Pakistan.

Has Wild Poliovirus Been Eliminated from Nigeria?

Wild poliovirus type 3 (WPV3) has not been seen anywhere since the last case of WPV3-associated paralysis in Nigeria in November 2012. At the time of writing, the most recent case of wild poliovirus type 1 (WPV1) in Nigeria occurred in July 2014, and WPV1 has not been seen in Africa since a case in Somalia in August 2014. No cases associated with circulating vaccine-derived type 2 poliovirus (cVDPV2) have been detected in Nigeria since November 2014. Has WPV1 been eliminated from Africa? Has WPV3 been eradicated globally? Has Nigeria interrupted cVDPV2 transmission? These questions are difficult because polio surveillance is based on paralysis and paralysis only occurs in a small fraction of infections. This report provides estimates for the probabilities of poliovirus elimination in Nigeria given available data as of March 31, 2015. It is based on a model of disease transmission that is built from historical polio incidence rates and is designed to represent the uncertainties in transmission dynamics and poliovirus detection that are fundamental to interpreting long time periods without cases. The model estimates that, as of March 31, 2015, the probability of WPV1 elimination in Nigeria is 84%, and that if WPV1 has not been eliminated, a new case will be detected with 99% probability by the end of 2015. The probability of WPV3 elimination (and thus global eradication) is > 99%. However, it is unlikely that the ongoing transmission of cVDPV2 has been interrupted; the probability of cVDPV2 elimination rises to 83% if no new cases are detected by April 2016.

Progress toward poliomyelitis eradication in Nigeria.

Transmission of wild poliovirus (WPV) has never been interrupted in Afghanistan, Pakistan, and Nigeria. Since 2003, infections with WPV of Nigerian origin have been detected in 25 polio-free countries. In 2012, the Nigerian government created an emergency operations center and implemented a national emergency action plan to eradicate polio. The 2013 revision of this plan prioritized (1) improving the quality of supplemental immunization activities (SIAs), (2) implementing strategies to reach underserved populations, (3) adopting special approaches in security-compromised areas, (4) improving outbreak response, (5) enhancing routine immunization and activities implemented between SIAs, and (6) strengthening surveillance. This report summarizes implementation of these activities during a period of unprecedented insecurity and violence, including the killing of health workers and the onset of a state of emergency in the northeast zone. This report reviews management strategies, innovations, trends in case counts, vaccination and social mobilization activities, and surveillance and monitoring data to assess progress in polio eradication in Nigeria. Nigeria has made significant improvements in the management of polio eradication initiative (pei) activities with marked improvement in the quality of SIAs, as measured by lot quality assurance sampling (LQAS). Comparing results from February 2012 with results from December 2013, the proportion of local government areas (LGAs) conducting LQAS in the 11 high-risk states at the ≥90% pass/fail threshold increased from 7% to 42%, and the proportion at the 80%-89% threshold increased from 9% to 30%. During January-December 2013, 53 polio cases were reported from 26 LGAs in 9 states in Nigeria, compared with 122 cases reported from 13 states in 2012. No cases of WPV type 3 infection have been reported since November 2012. In 2013, no polio cases due to any poliovirus type were detected in the northwest sanctuaries of Nigeria. In the second half of 2013, WPV transmission was restricted to Kano, Borno, Bauchi, and Taraba states. Despite considerable progress, 24 LGAs in 2012 and 7 LGAs in 2013 reported ≥2 cases, and WPV continued to circulate in 8 LGAs that had cases in 2012. Campaign activities were negatively impacted by insecurity and violence in Borno and Kano states. Efforts to interrupt transmission remain impeded by poor SIA implementation in localized areas, anti-polio vaccine sentiment, and limited access to vaccinate children because of insecurity. Sustained improvement in SIA quality, surveillance, and outbreak response and special strategies in security-compromised areas are needed to interrupt WPV transmission in 2014.

An Outbreak of Wild Poliovirus in the Republic of Congo, 2010-2011

The Republic of Congo has had no cases of wild poliovirus type 1 (WPV1) since 2000. In October 2010, a neurologist noted an abnormal number of cases of acute flaccid paralysis (AFP) among adults, which were later confirmed to be caused by WPV1. Those presenting with AFP underwent clinical history, physical examination, and clinical specimen collection to determine if they had polio. AFP cases were classified as laboratory-confirmed, clinical, or nonpolio AFP. Epidemiologic features of the outbreak were analyzed. From 19 September 2010 to 22 January 2011, 445 cases of WPV1 were reported in the Republic of Congo; 390 cases were from Pointe Noire. Overall, 331 cases were among adults; 378 cases were clinically confirmed, and 64 cases were laboratory confirmed. The case-fatality ratio (CFR) was 43%. Epidemiologic characteristics differed among polio cases reported in Pointe Noire and cases reported in the rest of the Republic of Congo, including age distribution and CFR. The outbreak stopped after multiple vaccination rounds with oral poliovirus vaccine, which targeted the entire population. This outbreak underscores the need to maintain high vaccination coverage to prevent outbreaks, the need to maintain timely high-quality surveillance to rapidly identify and respond to any potential cases before an outbreak escalates, and the need to perform ongoing risk assessments of immunity gaps in polio-free countries.

Wild Poliovirus Type 1, Central African Republic

To the Editor: In this article we summarize the investigation and response to the reemergence of wild poliovirus (WPV) type 1 in the Central African Republic (CAR) in 2003. Since 2000, reported annual routine vaccination coverage with >3 doses of oral polio vaccine (OPV) has been very low in CAR (<50%); National Immunization Days have been conducted every year since 1996, except in 2002 (1). From December 2003 to November 2004, the active acute flaccid paralysis surveillance system reported 112 cases of acute flaccid paralysis suspected to be poliomyelitis and 4 deaths (case-fatality ratio 4%). Fecal samples were collected and sent to the Institut Pasteur de Bangui. WPV type 1 (WPV1) was isolated in 30 cases (27%), vaccine polioviruses in 15 cases (5 type 1, 5 type 2, and 6 type 3) (13%), and nonpolio enteroviruses in 18 cases (16%). Epidemiologic investigations showed that 97% of patients with poliomyelitis received <3 doses of OPV and 93% of patients were <5 years of age. Isolates were sent to the National Institute for Virology in Johannesburg, South Africa, for sequencing. All viruses were type 1 and could be traced to common ancestral strains that circulate in disease-endemic reservoirs shared by northern Nigeria and southern Niger (WEAF-B genotype). The first importation occurred in Chad in August 2003 from northeastern Nigeria, and the outbreak spread to the adjacent countries of Cameroon in October 2003 and the CAR in December 2003. In CAR, the first case occurred in a 19-month-old child living in Ndjoh village north of Bossembele in Ombela M'Poko. A special mission by the World Health Organization/CAR officer determined that the child had not received OPV and had traveled 200 km into a northern region a few weeks before the onset date of December 16, 2003. The last case of acute flaccid paralysis in this region was noted on November 23, 1999. Supplemental immunization activities were conducted from March to April 2004. However, collected funds were not enough to cover the entire country, and only sanitary regions 1, 3, 4, 5, and 7 were included. The OPV coverage rate was estimated at 104% for the first round and 141% for the second round (CAR Ministry of Health, unpub. data). The second case occurred in April 2004 in Gadzi in sanitary region 2 in a 6-year-old nomad child who had not received OPV. The third case occurred in May 2004, in a village near where the second case was diagnosed, in a 23-month-old child who had not received OPV. Twenty-five other cases occurred between July and November in sanitary region 2 (Figure). Figure Supplementary immunization activities (SIA) areas, military conflicts, and migration movements, Central African Republic, 2001–2004. Gray star indicates first case of wild poliovirus type 1, Ombella-M'Poko (SR1), 2003; white stars indicate 2004 ... This outbreak is the largest epidemic of WPV1 in CAR since July 2000, when the last case of WPV1 was isolated (2). Probable reestablishment of endemic poliovirus and possible diffusion of WPV1 to countries further south, such as the Democratic Republic of Congo, is a concern. Four main reasons may explain this outbreak: 1) the close links with countries, such as Chad and Cameroon, where WPV1 recently reemerged; 2) declining rates of routine vaccination and low population immunity after disruption of health service infrastructures and road networks; 3) displaced persons' living in crowded areas with little sanitation and poor water supply; and 4) lack of response preparedness to WPV importation. Epidemiologic investigation of the first case was not conducted until >1 month after onset and implementation of the polio immunization initiative in a limited area. In May 2004, a decision was made by African Union health ministers to conduct a series of synchronized poliovirus campaigns across the African continent. Four rounds of National Immunization Days were conducted in CAR from August to December 2004. The OPV coverage rate in 600,000 children <5 years of age was estimated to be 89% in August, 98% in September, 102% in November, and 100% in December. Since November 2004, only 1 WPV1 case has been virologically confirmed in sanitary region 2. WPV1 has not been isolated in 2005. To restore the gains made in polio eradication in Central Africa, WPV transmission must be interrupted in Nigeria and Niger (3). Until then, neighboring countries must implement high routine vaccination coverage and high-quality, supplemental immunization activities. In 2002, these steps successfully prevented importation of WPV into Bangladesh and Nepal during a resurgence of polio in India. Surveillance standards must also be maintained to ensure the rapid detection of any WPV importation, thus allowing timely response and containment.