UNASSIGNED: The route of transmission of wild and circulating vaccine-derived polioviruses remains controversial, between respiratory and faecal-oral, and we aim to identify the most plausible one to settle the controversy.
UNASSIGNED: We explored available epidemiological clues and evidence in support of either route in order to arrive at an evidence-based conclusion.
UNASSIGNED: Historically the original concept was respiratory transmission based on epidemiological features of age distribution, which was later revised to faecal-oral as the rationale for popularising the live attenuated oral polio vaccine in preference to the inactivated poliovirus vaccine. Through epidemiological logic, we find no evidence for the faecal-oral route from available studies and observations, but all available information supports the respiratory route.
UNASSIGNED: The route is respiratory, not faecal-oral. The global polio eradication initiative assumed it was faecal-oral - and its gargantuan efforts based on this assumption have failed in two ways: eradication remains pending and circulating vaccine-derived polioviruses have seeded widely. With clarity on the route of transmission the choice of vaccine is also clear - it can only be the inactivated poliovirus vaccine.

Polio is an infectious and disabling life-threatening disease caused by the poliovirus. This disease is prevented through vaccination. Though this viral infection has been eliminated in most parts of the world, a few countries are still endemic to wild poliovirus. In 2020, the World Health Organization (WHO) African Region, including Cameroon, was certified free of wild poliovirus. Some countries recurrently report circulating vaccine-derived poliovirus cases (cVDPV) despite recorded achievements. Also, the risk of importing poliovirus from endemic settings remains, particularly in the context of coronavirus disease (COVID-19). This study aimed to assess the state of polio in Cameroon and identify the situation during COVID-19. A data review was conducted from February to March 2023. Data on polio cases and vaccination coverage per region of Cameroon were reviewed from 2014 to 2022. Data were analyzed with Microsoft Excel, and the results were presented as proportions. The last wild poliovirus was reported in Cameroon in 2014, and the country benefitted from a response. No case of poliovirus was detected in the country from 2015 to 2018. After that, an increasing number of type two cVDPV were reported across 50% of the country\'s regions from 2019 to 2022. The outbreaks benefitted from responses with various oral polio vaccines, including the type two novel oral polio vaccine (nOPV-2). Though wild polioviruses have been eliminated in most countries, including Cameroon, cVDPV remains a significant problem. There is an urgent need to strengthen disease surveillance and vaccination to prevent cVDPV-2 in this country, particularly in the COVID-19 context.

Trivalent oral poliovirus vaccine (tOPV) was globally replaced with bivalent oral poliovirus vaccine (bOPV) in April 2016 (\"the switch\"). Many outbreaks of paralytic poliomyelitis associated with type 2 circulating vaccine-derived poliovirus (cVDPV2) have been reported since this time. The Global Polio Eradication Initiative (GPEI) developed standard operating procedures (SOPs) to guide countries experiencing cVDPV2 outbreaks to implement timely and effective outbreak response (OBR). To assess the possible role of compliance with SOPs in successfully stopping cVDPV2 outbreaks, we analyzed data on critical timelines in the OBR process.
Data were collected on all cVDPV2 outbreaks detected for the period April 1, 2016 and December 31, 2020 and all outbreak responses to those outbreaks between April 1, 2016 and December 31, 2021. We conducted secondary data analysis using the GPEI Polio Information System database, records from the U.S. Centers for Disease Control and Prevention Polio Laboratory, and meeting minutes of the monovalent OPV2 (mOPV2) Advisory Group. Date of notification of circulating virus was defined as Day 0 for this analysis. Extracted process variables were compared with indicators in the GPEI SOP version 3.1.
One hundred and eleven cVDPV2 outbreaks resulting from 67 distinct cVDPV2 emergences were reported during April 1, 2016-December 31, 2020, affecting 34 countries across four World Health Organization Regions. Out of 65 OBRs with the first large-scale campaign (R1) conducted after Day 0, only 12 (18.5%) R1s were conducted by the target of 28 days after Day 0. Of the 89 OBRs with the second large-scale campaign (R2) conducted after Day 0, 30 (33.7%) R2s were conducted by the target of 56 days after Day 0. Twenty-three (31.9%) of the 72 outbreaks with isolates dated after Day 0 were stopped within the 120-day target.
Since \"the switch\", delays in OBR implementation were evident in many countries, which may be related to the persistence of cVDPV2 outbreaks >120 days. To achieve timely and effective response, countries should follow GPEI OBR guidelines.

Genetic variants of vaccine poliovirus type 2, imported from an unknown source, were detected in waste waters in Jerusalem, London and New York in early 2022. Wild poliovirus type 2 was globally eradicated in 1999, but vaccine virus type 2 continued for 16 more years; routine use of the vaccine was discontinued in 2016 and reintroduced occasionally on purpose. As an unintended consequence, type 2 vaccine virus variants (circulating vaccine-derived polioviruses, cVDPVs) that mimic wild viruses\' contagiousness and neurovirulence, have been emerging and spreading. To illustrate, in just the past four years (2018-2021), 2296 children developed cVDPV polio in 35 low-income countries. Many assume that virus transmission is via the faecal-oral route. Sustained virus transmission was documented in London and New York, in spite of high standards of sanitation and hygiene. Here, virus transmission cannot be attributed to faecal contamination of food or drinking water (for faecal-oral transmission). Hence, contagious transmission can only be explained by inhalation of droplets/aerosol containing virus shed in pharyngeal fluids (respiratory transmission), as was the classical teaching of polio epidemiology. If transmission efficiency of VDPV is via the respiratory route where hygiene is good, it stands to reason that it is the same case in countries with poor hygiene, since poor hygiene cannot be a barrier against respiratory transmission. By extrapolation, the extreme transmission efficiency of wild polioviruses must also have been due to their ability to exploit respiratory route transmission. These lessons have implications for global polio eradication. It was as a result of assuming faecal-oral transmission that eradication was attempted with live attenuated oral polio vaccine (OPV), ignoring its safety problems and very low efficacy in low-income countries. Inactivated poliovirus vaccine (IPV) is completely safe and highly efficacious in protecting children against polio, with just three routine doses. Protecting all children from polio must be the interim goal of eradication, until poliovirus circulation dies out under sustained immunisation pressure. OPV should be discontinued under cover of immunity induced by IPV to stop the emergence of new lineages of VDPVs, not only type 2, but also types 1 and 3, to expedite the completion of polio eradication.

The number and geographic breadth of circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreaks detected after the withdrawal of type 2 containing oral polio vaccine (April 2016) have exceeded forecasts.Using Acute Flaccid Paralysis (AFP) investigations and environmental surveillance (ES) data from the Global Polio Laboratory Network, we summarize the epidemiology of cVDPV2 outbreaks. Between 01 January 2016 to 31 December 2020, a total of 68 unique cVDPV2 genetic emergences were detected across 34 countries. The cVDPV2 outbreaks have been associated with 1596 acute flaccid paralysis cases across four World Health Organization regions: 962/1596 (60.3%) cases occurred in African Region; 619/1596 (38.8%) in the Eastern Mediterranean Region; 14/1596 (0.9%) in Western-Pacific Region; and 1/1596 (0.1%) in the European Region. As the majority of the cVDPV2 outbreaks have been seeded through monovalent type 2 oral poliovirus vaccine (mOPV2) use in outbreak responses, the introduction of the more stable novel oral poliovirus vaccine will be instrumental in stopping emergence of new cVDPV2 lineages.

Delivering inactivated poliovirus vaccine (IPV) with oral poliovirus vaccine (OPV) in campaigns has been explored to accelerate the control of type 2 circulating vaccine-derived poliovirus (cVDPV) outbreaks. A review of scientific literature suggests that among populations with high prevalence of OPV failure, a booster with IPV after at least two doses of OPV may close remaining humoral and mucosal immunity gaps more effectively than an additional dose of trivalent OPV. However, IPV alone demonstrates minimal advantage on humoral immunity compared with monovalent and bivalent OPV, and cannot provide the intestinal immunity that prevents infection and spread to those individuals not previously exposed to live poliovirus of the same serotype (i.e. type 2 for children born after the switch from trivalent to bivalent OPV in April 2016). A review of operational data from polio campaigns shows that addition of IPV increases the cost and logistic complexity of campaigns. As a result, campaigns in response to an outbreak often target small areas. Large campaigns require a delay to ensure logistics are in place for IPV delivery, and may need implementation in phases that last several weeks. Challenges to delivery of injectable vaccines through house-to-house visits also increases the risk of missing the children who are more likely to benefit from IPV: those with difficult access to routine immunization and other health services. Based upon this information, the Strategic Advisory Group of Experts in immunization (SAGE) recommended in October 2020 the following strategies: provision of a second dose of IPV in routine immunization to reduce the risk and number of paralytic cases in countries at risk of importation or new emergences; and use of type 2 OPV in high-quality campaigns to interrupt transmission and avoid seeding new type 2 cVDPV outbreaks.

Concurrent outbreaks of circulating vaccine-derived poliovirus serotypes 1 and 2 (cVDPV1, cVDPV2) were confirmed in the Republic of the Philippines in September 2019 and were subsequently confirmed in Malaysia by early 2020. There is continuous population subgroup movement in specific geographies between the two countries. Outbreak response efforts focused on sequential supplemental immunization activities with monovalent Sabin strain oral poliovirus vaccine type 2 (mOPV2) and bivalent oral poliovirus vaccines (bOPV, containing Sabin strain types 1 and 3) as well as activities to enhance poliovirus surveillance sensitivity to detect virus circulation. A total of six cVDPV1 cases, 13 cVDPV2 cases, and one immunodeficiency-associated vaccine-derived poliovirus type 2 case were detected, and there were 35 cVDPV1 and 31 cVDPV2 isolates from environmental surveillance sewage collection sites. No further cVDPV1 or cVDPV2 have been detected in either country since March 2020. Response efforts in both countries encountered challenges, particularly those caused by the global COVID-19 pandemic. Important lessons were identified and could be useful for other countries that experience outbreaks of concurrent cVDPV serotypes.

In addition to affecting individual health the COVID-19 pandemic has disrupted efforts to deliver essential health services around the world. In this article we present an overview of the immediate programmatic and epidemiologic impact of the pandemic on polio eradication as well as the adaptive strategic and operational measures taken by the Global Polio Eradication Initiative (GPEI) from March through September 2020. Shortly after the World Health Organization (WHO) declared a global pandemic on 11 March 2020, the GPEI initially redirected the programme\'s assets to tackle COVID-19 and suspended house-to-house supplementary immunization activities (SIAs) while also striving to continue essential poliovirus surveillance functions. From March to May 2020, 28 countries suspended a total of 62 polio vaccine SIAs. In spite of efforts to continue poliovirus surveillance, global acute flaccid paralysis (AFP) cases reported from January-July 2020 declined by 34% compared with the same period in 2019 along with decreases in the mean number of environment samples collected per active site in the critical areas of the African and Eastern Mediterranean regions. The GPEI recommended countries should resume planning and implementation of SIAs starting in July 2020 and released guidelines to ensure these could be done safely for front line workers and communities. By the end of September 2020, a total of 14 countries had implemented circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreak response vaccination campaigns and Afghanistan and Pakistan restarted SIAs to stop ongoing wild poliovirus type 1 (WPV1) transmission. The longer-term impacts of disruptions to eradication efforts remain to be determined, especially in terms of the effect on poliovirus epidemiology. Adapting to the pandemic situation has imposed new considerations on program implementation and demonstrated not only GPEI\'s contribution to global health security, but also identified potential opportunities for coordinated approaches across immunization and health services.

BACKGROUND: Polio is a disabling and potentially deadly disease caused by a wild poliovirus and vaccine-derived poliovirus. The purpose of this review is to discuss the current situation of polio in Ethiopia.
METHODS: Relevant scientific articles on Polio were searched from different data bases and websites.
RESULTS: The first wild poliovirus in Ethiopia was detected in 1999, followed by detection of few cases in 2000 and 2001. No wild poliovirus was detected in Ethiopia for the next 3 years (2001-2003). However, the disease resurged again in the country between 2004 and 2008 due to challenge to provide sufficient oral poliovirus vaccine coverage, migration and cross border economic activities and lack of good acute flaccid paralysis surveillance. After almost 5 years with no wild polio virus, Ethiopia again affected by polio outbreak importation in 2013. However, due to multiple supplementary immunization activities campaigns of improved quality and enhanced surveillance, the outbreak was eventually successfully interrupted within 6 months of confirmation. The most recent emergence of polio in Ethiopia has seen in this year (2020) six years after the country documented zero polio cases since 2014. The cause of the resurgence of the disease is circulating vaccine derived polio virus-2. Currently, Ethiopia has been conducting outbreak response by declaring Mop-up campaigns since September 2020.
CONCLUSIONS: Therefore, it can be recommended that: - 1. The country has to completely shift from oral polio virus vaccine to inactivated polio vaccine so that the risk of vaccine derived polio will be diminished; 2. Ethiopia has to strengthen the mop up campaign that it has started in September 2020 following the reemergence of the disease in the country; 3. Ethiopia has to strengthen surveillance for acute flaccid paralysis in order to rapidly detect any new virus importation and to facilitate a rapid response.

On August 25, 2019, the Noguchi Memorial Institute for Medical Research notified the confirmation of a circulating-vaccine-derived poliovirus type-2 (cVDPV2) from the Agbogbloshie environmental surveillance (AES) site, in the Greater Accra Region. A field investigation of the outbreak was conducted to describe the results of epidemiological and laboratory investigations, and control efforts.
We conducted a descriptive investigation, records review, and active-case-search. Caregivers were interviewed on the vaccination status of their children; knowledge, attitude, and practices on polio prevention; water, sanitation and hygiene practices, and health-seeking behaviors. Stool from healthy children <5 y and sewage samples were taken for laboratory diagnosis.
cVDPV2 genetically similar to the cVDPV2 diagnosed recently in the Northern Region of Ghana and Nigeria was identified. 2019 half-year coverage of OPV and IPV was 22%. Fully immunized children were 49% (29/59). Most health workers (70%) had a fair knowledge of polio and acute flaccid paralysis (AFP). Forty-six percent of care-givers admitted to using the large drain linked to the site where the cVDPV2 was isolated as their place of convenience and disposing of the fecal matter of their children. No AFP case was identified. Stool samples from 40 healthy children yielded non-polio enteroviruses while 75% (3/4) of the additional sewage samples yielded cVDPV2.
cVDPV2 was isolated from the AES site. No AFP or poliovirus was identified from healthy children. There is a need to improve health workers\' knowledge on AFP and to address the dire sanitation conditions in the Agbogbloshie market and its environs.