Effective case/infection ratio of poliomyelitis in vaccinated populations

Persistence of poliovirus types 2 and 3 in waste-impacted water and sediment

Eradication of poliovirus (PV) is a global public health priority, and as clinical cases decrease, the role of environmental surveillance becomes more important. Persistence of PV and the environmental factors that influence it (such as temperature and sample type) are an important part of understanding and interpreting positive environmental surveillance samples. The objective of this study was to evaluate the persistence of poliovirus type 2 (PV2) and type 3 (PV3) in wastewater and sediment. Microcosms containing either 1) influent wastewater or 2) influent wastewater with a sediment matrix were seeded with either PV2 or PV3, and stored for up to 126 days at three temperatures (4°C, room temperature [RT], and 30°C). Active PV in the liquid of (1), and the sediment and liquid portions of (2) were sampled and quantified at up to 10 time points via plaque assay and RT-qPCR. A suite of 17 models were tested for best fit to characterize decay of PV2 and PV3 over time and determine the time points at which >90% (T90) and >99% (T99) reduction was reached. Linear models assessed the influence of experimental factors (matrix, temperature, virus type and method of detection) on the predicted T90 and T99 values. Results showed that when T90 was the dependent variable, virus type, matrix, and temperature significantly affected decay, and there was a clear interaction between the sediment matrix and temperature. When T99 was the dependent variable, only temperature and matrix type significantly influenced the decay metric. This study characterizes the persistence of both active and molecular PV2 and PV3 in relevant environmental conditions, and demonstrates that temperature and sediment both play important roles in PV viability. As eradication nears and clinical cases decrease, environmental surveillance and knowledge of PV persistence will play a key role in understanding the silent circulation in endemic countries.

Review of poliovirus modeling performed from 2000 to 2019 to support global polio eradication

INTRODUCTION

Over the last 20 years (2000-2019) the partners of the Global Polio Eradication Initiative (GPEI) invested in the development and application of mathematical models of poliovirus transmission as well as economics, policy, and risk analyses of polio endgame risk management options, including policies related to poliovirus vaccine use during the polio endgame.

AREAS COVERED

This review provides a historical record of the polio studies published by the three modeling groups that primarily performed the bulk of this work. This review also systematically evaluates the polio transmission and health economic modeling papers published in English in peer-reviewed journals from 2000 to 2019, highlights differences in approaches and methods, shows the geographic coverage of the transmission modeling performed, identified common themes, and discusses instances of similar or conflicting insights or recommendations.

EXPERT OPINION

Polio modeling performed during the last 20 years substantially impacted polio vaccine choices, immunization policies, and the polio eradication pathway. As the polio endgame continues, national preferences for polio vaccine formulations and immunization strategies will likely continue to change. Future modeling will likely provide important insights about their cost-effectiveness and their relative benefits with respect to controlling polio and potentially achieving and maintaining eradication.

Global dynamics of a mathematical model for the possible re-emergence of polio

Motivated by studies warning about a possible re-emergence of poliomyelitis in Europe, we analyse a compartmental model for the transmission of polio describing the possible effect of unvaccinated people arriving to a region with low vaccination coverage. We calculate the basic reproduction number, and determine the global dynamics of the system: we show that, depending on the parameters, one of the two equilibria is globally asymptotically stable. The main tools applied are Lyapunov functions and persistence theory. We illustrate the analytic results by numerical examples, which also suggest that in order to avoid the risk of polio re-emergence, vaccinating the immigrant population might result insufficient, and also the vaccination coverage of countries with low rates should be increased.

Polio and Measles Down the Drain: Environmental Enterovirus Surveillance in the Netherlands, 2005 to 2015

Polioviruses (PVs) are members of the genus Enterovirus In the Netherlands, the exclusion of PV circulation is based on clinical enterovirus (EV) surveillance (CEVS) of EV-positive cases and routine environmental EV surveillance (EEVS) conducted on sewage samples collected in the region of the Netherlands where vaccination coverage is low due to religious reasons. We compared the EEVS data to those of the CEVS to gain insight into the relevance of EEVS for poliovirus and nonpolio enterovirus surveillance. Following the polio outbreak in Syria, EEVS was performed at the primary refugee center in Ter Apel in the Netherlands, and data were compared to those of CEVS and EEVS. Furthermore, we assessed the feasibility of poliovirus detection by EEVS using measles virus detection in sewage during a measles outbreak as a proxy. Two Sabin-like PVs were found in routine EEVS, 11 Sabin-like PVs were detected in the CEVS, and one Sabin-like PV was found in the Ter Apel sewage. We observed significant differences between the three programs regarding which EVs were found. In 6 sewage samples collected during the measles outbreak in 2013, measles virus RNA was detected in regions where measles cases were identified. In conclusion, we detected PVs, nonpolio EVs, and measles virus in sewage and showed that environmental surveillance is useful for poliovirus detection in the Netherlands, where live oral poliovirus vaccine is not used and communities with lower vaccination coverage exist. EEVS led to the detection of EV types not seen in the CEVS, showing that EEVS is complementary to CEVS.IMPORTANCE We show that environmental enterovirus surveillance complements clinical enterovirus surveillance for poliovirus detection, or exclusion, and for nonpolio enterovirus surveillance. Even in the presence of adequate surveillance, only a very limited number of Sabin-like poliovirus strains were detected in a 10-year period, and no signs of transmission of oral polio vaccine (OPV) strains were found in a country using exclusively inactivated polio vaccine (IPV). Measles viruses can be detected during an outbreak in sewage samples collected and concentrated following procedures used for environmental enterovirus surveillance.

Eradicating polio in Pakistan: an analysis of the challenges and solutions to this security and health issue

Since the launch of the Global Polio Eradication Initiative (GPEI) in 1988 the global incidence of poliomyelitis has fallen by nearly 99 %. From a situation where wild type poliovirus was endemic in 125 countries across five continents, transmission is now limited to regions of just three countries – Pakistan, Afghanistan and Nigeria. A sharp increase in Pakistan’s poliomyelitis cases in 2014 prompted the International Health Regulations Emergency Committee to declare the situation a ‘public health emergency of international concern’. Global polio eradication hinges on Pakistan’s ability to address the religious, political and socioeconomic barriers to immunisation; including discrepancies in vaccine coverage, a poor health infrastructure, and conflict in polio-endemic regions of the country. This analysis provides an overview of the GPEI, focusing on the historical and contemporary challenges facing Pakistan’s polio eradication programme and the impact of conflict and insecurity, and sheds light on strategies to combat vaccine hesitancy, engage local communities and build on recent progress towards polio eradication in Pakistan.