Polio outbreak: An ongoing but ignored public health emergency of international concern – Correspondence

Dear Editor, Poliomyelitis is an acute communicable disease caused by a single-stranded RNA enterovirus with 3 serotypes of poliovirus (Type1,2,3) causing an irreversible paralytic disease that occurs in about 0.5% of poliovirus infections in children less than 5 years of age (1 in every 200 susceptible children affected). The remaining infected individuals are either asymptomatic or show flu-like symptoms. Approximately 5–10% of paralytic patients may die due to respiratory muscle paralysis. Polio has no cure, but the inactivated polio vaccine (IPV) and live-attenuated oral polio vaccine (OPV) are effective in preventing infection by all poliovirus types: type 1, type 2, and type 3. The disease is transmitted through fecal-oral and oral-oral routes depending on the level of sanitation, with the fecal-oral route being the primary method of transmission for polioviruses, the virus replicates in the intestine, from where they can be shed in the feces or affect the nervous system. In 1988, the WHO started the Global Polio Eradication Initiative (GPEI) to eradicate polio. Since then, a significant decline has been in the number of wild poliovirus infections (WPV); from 350 000 cases in 1988 to 650 cases in 2011, and most recently 6 cases in 2021 globally [1]. Since 1999, there have been no reported cases of wild poliovirus type 2, while the last case of wild poliovirus type 3 occurred in 2012. Both strains were declared to be globally eradicated in 2015 and 2019, respectively. Currently, WPV type 1 is the only strain that causes polio, and in 2022, it continues to be endemic only in Pakistan and Afghanistan [2]. However, the OPV attenuated virus can mutate to regain neurovirulence, particularly in areas with low vaccination coverage where the population has low immunity. The uninterrupted circulation of the attenuated virus can thus increase the likelihood of its mutation and lead to circulating vaccine-derived poliovirus (cVDPV) outbreaks [3,4]. Around 800 cases of cVDPV were reported between the years 2000 and 2015, with the prime contributor being cVDPV type 2 [5,6]. As a response to the vaccine-derived disease clusters, the trivalent vaccine (containing types 1, 2, and 3) was switched in 2016 to the bivalent vaccine (containing types 1 and 3), together with providing IPV into routine vaccination programs to maintain immunity against all polioviruses, including poliovirus type 2. This switch aimed to eradicate both wild polioviruses and cVDVP simultaneously [7]. However, more cVDPV outbreaks, infected cases, affected countries, and new genetic emergence have been reported since then. Between January 2016 and August 30, 2022, cVDPV affected approximately 2660 cases, 96% of which were caused by cVDVP2, primarily in countries with low vaccine coverage, exceeding the number of those infected with the wild types (Fig. 1) [3,4].Fig. 1.: The trend of polio cases from 2000 to August 30, 2022. Data are from WHO (https://extranet.who.int/polis/public/CaseCount.aspx) and GPEI (https://polioeradication.org/polio-today/polio-now/this-week/circulating-vaccine-derived-poliovirus/).The cessation of the type 2 component of trivalent OPV and the delay in IPV introduction may be the causes of the early rise in the outbreaks. Since 2019, the outbreaks have substantially increased, probably due to using mono OPV type 2 (mOPV2) to control cVDVP2 outbreaks, leading to around 60 new genetic emergence [4]. Moreover, the COVID-19 pandemic, which delayed routine vaccination, delivery of the mOPV2 in response to outbreaks, and suspended field surveillance, may have contributed to the dramatic rise in cases observed in 2020, reaching the highest number of cases ever recorded. Since the early 2000s, high-income countries such as the US, the UK, and Scandinavia have used the IPV vaccine alone to eradicate vaccine-derived and wild polio. However, IPV is five times more expensive than OPV and more difficult to administer. Furthermore, IPV is less effective at interrupting the transmission of infection, particularly during outbreaks, since it offers less intestinal immunity than OPV, allowing for viral replication in the intestine and shedding in the feces. These factors limit IPV's ability to control cVDPV2 outbreaks in countries with low vaccination rates and limited resources [8]. A novel OPV type 2 (nOPV2) vaccine was developed and granted Emergency Use Listing in 2021. It outperformed the conventional mOPV2 regarding genetic stability and the likelihood of not seeding new VDPV outbreaks [9]. The introduction of the novel vaccine as the primary vaccine in response to VDPV type 2 outbreaks is one of the primary strategies of the Polio Eradication Strategy 2022–2026 launched by GPEI [10]. Polio cases are currently being reported from various Asian and African countries (Table 1). However, in 2022, cVDPV2 was found in sewage in London, UK and Israel, and a paralytic case caused by the virus was reported in a county with the highest immunization coverage in New York state, USA [11]. In November 2021, Malawi reported the first WPV type 1 paralytic case in Africa since 2016. This virus strain was related to one found previously in Pakistan. Later in July 2022, five cases were reported from Mozambique, a neighboring country [12]. As a result, the risk of wild or vaccine-associated poliovirus reemergence remains in countries that have eradicated wild polioviruses or stopped using the OPV vaccine in routine immunization. This will continue to be a challenge as long as there are unvaccinated groups, or the virus has not been eradicated globally. Poliovirus eradication should be prioritized again, with high immunization coverage rates maintained and mOPV2 replaced with nOPV2 in the outbreak response. Country-specific precise and individualized strategy is required to eradicate WPV and cVDPV simultaneously. We recommend enhancing acute flaccid paralysis surveillance and environmental surveillance for all cases reported globally. We also believe it is imperative to address the ‘anticipated vaccination needs’ through behavior change communication and focused group discussions to improve vaccine acceptability and coverage in all pockets.Table 1: Prevalence of polio cases in 2022. Data are from GPEI (https://polioeradication.org/polio-today/polio-now/this-week/, https://polioeradication.org/polio-today/polio-now/).Provenance and peer review Not commissioned, internally peer-reviewed. Data statement Data not available/not applicable. Sources of funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Ethical approval Not applicable. Research Registration Unique Identifying Number (UIN) Name of the registry: N/A Unique Identifying number or registration ID: N/A Hyperlink to your specific registration (must be publicly accessible and will be checked): N/A Author contribution RAF: designed the study. RAF, HMS and YS: made the first draft. RAF: updated the manuscript. RAF and ZAM: reviewed the final draft and edited final. All authors have critically reviewed and approved the final draft and are responsible for the content and similarity index of the manuscript. Guarantor All authors. Declaration of competing interest No conflicts to declare. Ramadan Abdelmoez Farahat Hazem Mohamed Salamah Yashendra Sethi Ziad A. Memish 1Faculty of Medicine, Kafrelsheikh University, Kafrelsheikh, 33511, Egypt 2Faculty of Medicine, Zagazig University, Zagazig, Egypt 3Department of Medicine, Government Doon Medical College, Dehradun, India 4Research and Innovation Center, King Saud Medical City, Riyadh, Saudi Arabia 5College of Medicine, Alfaisal University, Riyadh, Saudi Arabia 6Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA E-mail addresses:[email protected]