Polio eradication: the OPV paradox

Wastewater-based surveillance as a tool for public health action: SARS-CoV-2 and beyond

Wastewater-based surveillance (WBS) has undergone dramatic advancement in the context of the coronavirus disease 2019 (COVID-19) pandemic. The power and potential of this platform technology were rapidly realized when it became evident that not only did WBS-measured SARS-CoV-2 RNA correlate strongly with COVID-19 clinical disease within monitored populations but also, in fact, it functioned as a leading indicator. Teams from across the globe rapidly innovated novel approaches by which wastewater could be collected from diverse sewersheds ranging from wastewater treatment plants (enabling community-level surveillance) to more granular locations including individual neighborhoods and high-risk buildings such as long-term care facilities (LTCF). Efficient processes enabled SARS-CoV-2 RNA extraction and concentration from the highly dilute wastewater matrix. Molecular and genomic tools to identify, quantify, and characterize SARS-CoV-2 and its various variants were adapted from clinical programs and applied to these mixed environmental systems. Novel data-sharing tools allowed this information to be mobilized and made immediately available to public health and government decision-makers and even the public, enabling evidence-informed decision-making based on local disease dynamics. WBS has since been recognized as a tool of transformative potential, providing near-real-time cost-effective, objective, comprehensive, and inclusive data on the changing prevalence of measured analytes across space and time in populations. However, as a consequence of rapid innovation from hundreds of teams simultaneously, tremendous heterogeneity currently exists in the SARS-CoV-2 WBS literature. This manuscript provides a state-of-the-art review of WBS as established with SARS-CoV-2 and details the current work underway expanding its scope to other infectious disease targets.

Evolution of global polio eradication strategies: targets, vaccines, and supplemental immunization activities (SIAs)

BACKGROUND

Despite multiple revisions of targets and timelines in polio eradication plans since 1988, including changes in supplemental immunization activities (SIAs) that increase immunity above routine immunization (RI) coverage, poliovirus transmission continues as of 2024.

METHODS

We reviewed polio eradication plans and Global Polio Eradication Initiative (GPEI) annual reports and budgets to characterize key phases of polio eradication, the evolution of poliovirus vaccines, and the role of SIAs. We used polio epidemiology to provide context for successes and failures and updated prior modeling to show the contribution of SIAs in achieving and maintaining low polio incidence compared to expected incidence for the counterfactual of RI only.

RESULTS

We identified multiple phases of polio eradication that included shifts in targets and timelines and the introduction of different poliovirus vaccines, which influenced polio epidemiology. Notable shifts occurred in GPEI investments in SIAs since 2001, particularly since 2016. Modeling results suggest that SIAs play(ed) a key role in increasing (and maintaining) high population immunity to levels required to eradicate poliovirus transmission globally.

CONCLUSIONS

Shifts in polio eradication strategy and poliovirus vaccine usage in SIAs provide important context for understanding polio epidemiology, delayed achievement of polio eradication milestones, and complexity of the polio endgame.

Oral and fecal polio vaccine excretion following bOPV vaccination among Israeli infants

INTRODUCTION

Inactivated polio virus (IPV) vaccinations are a mainstay of immunization schedules in developed countries, while oral polio vaccine (OPV) is administered in developing countries and is the main vaccine in outbreaks. Due to circulating wild poliovirus (WPV1) detection in Israel (2013), oral bivalent polio vaccination (bOPV) was administered to IPV primed children and incorporated into the vaccination regimen.

OBJECTIVES

We aimed to determine the extent and timeframe of fecal and salivary polio vaccine virus (Sabin strains) shedding following bOPV vaccination among IPV primed children.

METHODS

Fecal samples were collected from a convenience sample of infants and toddlers attending 11 Israeli daycare centers. Salivary samples were collected from infants and toddlers following bOPV vaccination.

RESULTS

398 fecal samples were collected from 251 children (ages: 6-32 months), 168 received bOPV vaccination 4-55 days prior to sample collection. Fecal excretion continued among 80 %, 50 %, and 20 %, 2, 3, and 7 weeks following vaccination. There were no significant differences in the rate and duration of positive samples among children immunized with 3 or 4 IPV doses. Boys were 2.3-fold more likely to excrete the virus (p = 0.006). Salivary shedding of Sabin strains occurred in 1/47 (2 %) and 1/49 (2 %) samples 4, and 6 days following vaccination respectively.

CONCLUSIONS

Fecal detection of Sabin strains among IPV-primed children continues for 7 weeks; additional doses of IPV do not augment intestinal immunity; limited salivary shedding occurs for up to a week. This data can enhance understanding of intestinal immunity achieved by different vaccination schedules and guide recommendations for contact precautions of children following bOPV vaccination.

Health economic analysis of vaccine options for the polio eradication endgame: 2022-2036

BACKGROUND

: Multiple vaccine options are available for polio prevention and risk management. Integrated global risk, economic, and poliovirus transmission modeling provides a tool to explore the dynamics of ending all use of one or more poliovirus vaccines to simplify the polio eradication endgame.

RESEARCH DESIGN AND METHODS

: With global reported cases of poliomyelitis trending higher since 2016, we apply an integrated global model to simulate prospective vaccine policies and strategies for OPV-using countries starting with initial conditions that correspond to the epidemiological poliovirus transmission situation at the beginning of 2022.

RESULTS

: Abruptly ending all OPV use in 2023 and relying only on IPV to prevent paralysis with current routine immunization coverage would lead to expected reestablished endemic transmission of poliovirus types 1 and 2, and approximately 150,000 expected cases of poliomyelitis per year. Alternatively, if OPV-using countries restart trivalent OPV (tOPV) use for all immunization activities and end IPV use, the model shows the lowest anticipated annual polio cases and lowest costs.

CONCLUSIONS

: Poor global risk management and coordination of OPV cessation remain a critical failure mode for the polio endgame, and national and global decision makers face difficult choices due to multiple available polio vaccine options and immunization strategies.

Inferring Numbers of Wild Poliovirus Excretors Using Quantitative Environmental Surveillance

Response to and monitoring of viral outbreaks can be efficiently focused when rapid, quantitative, kinetic information provides the location and the number of infected individuals. Environmental surveillance traditionally provides information on location of populations with contagious, infected individuals since infectious poliovirus is excreted whether infections are asymptomatic or symptomatic. Here, we describe development of rapid (1 week turnaround time, TAT), quantitative RT-PCR of poliovirus RNA extracted directly from concentrated environmental surveillance samples to infer the number of infected individuals excreting poliovirus. The quantitation method was validated using data from vaccination with bivalent oral polio vaccine (bOPV). The method was then applied to infer the weekly number of excreters in a large, sustained, asymptomatic outbreak of wild type 1 poliovirus in Israel (2013) in a population where >90% of the individuals received three doses of inactivated polio vaccine (IPV). Evidence-based intervention strategies were based on the short TAT for direct quantitative detection. Furthermore, a TAT shorter than the duration of poliovirus excretion allowed resampling of infected individuals. Finally, the method documented absence of infections after successful intervention of the asymptomatic outbreak. The methodologies described here can be applied to outbreaks of other excreted viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), where there are (1) significant numbers of asymptomatic infections; (2) long incubation times during which infectious virus is excreted; and (3) limited resources, facilities, and manpower that restrict the number of individuals who can be tested and re-tested.

Polio eradication at the crossroads

The Global Polio Eradication Initiative, launched in 1988 with anticipated completion by 2000, has yet to reach its ultimate goal. The recent surge of polio cases urgently calls for a reassessment of the programme's current strategy and a new design for the way forward. We propose that the sustainable protection of the world population against paralytic polio cannot be achieved simply by stopping the circulation of poliovirus but must also include maintaining high rates of population immunity indefinitely, which can be created and maintained by implementing global immunisation programmes with improved poliovirus vaccines that create comprehensive immunity without spawning new virulent viruses. The proposed new strategic goal of eradicating the disease rather than the virus would lead to a sustainable eradication of poliomyelitis while simultaneously promoting immunisation against other vaccine-preventable diseases.

Immunogenicity and Safety of Inactivated Sabin-Strain Polio Vaccine "PoliovacSin": Clinical Trials Phase I and II

Global polio eradication requires both safe and effective vaccines, and safe production processes. Sabin oral poliomyelitis vaccine (OPV) strains can evolve to virulent viruses and result in poliomyelitis outbreaks, and conventional inactivated poliomyelitis vaccine (Salk-IPV) production includes accumulation of large stocks of neurovirulent wild polioviruses. Therefore, IPV based on attenuated OPV strains seems a viable option. To increase the global supply of affordable inactivated vaccine in the still not-polio free world we developed an IPV made from the Sabin strains–PoliovacSin. Clinical trials included participants 18–60 years of age. A phase I single-center, randomized, double-blind placebo-controlled clinical trial included 60 participants, who received one dose of PoliovacSin or Placebo. A phase II multicenter, randomized, double-blind, comparative clinical trial included 200 participants, who received one dose of PoliovacSin or Imovax Polio. All vaccinations were well tolerated, and PoliovacSin had a comparable safety profile to the Placebo or the reference Imovax Polio preparations. A significant increase in neutralizing antibody levels to polioviruses types 1–3 (Sabin and wild) was observed in PoliovacSin and Imovax Polio vaccinated groups. Therefore, clinical trials confirmed good tolerability, low reactogenicity, and high safety profile of the PoliovacSin and its pronounced immunogenic properties. The preparation was approved for clinical trials involving infants.

Updated Characterization of Outbreak Response Strategies for 2019-2029: Impacts of Using a Novel Type 2 Oral Poliovirus Vaccine Strain

Delays in achieving the global eradication of wild poliovirus transmission continue to postpone subsequent cessation of all oral poliovirus vaccine (OPV) use. Countries must stop OPV use to end all cases of poliomyelitis, including vaccine-associated paralytic polio (VAPP) and cases caused by vaccine-derived polioviruses (VDPVs). The Global Polio Eradication Initiative (GPEI) coordinated global cessation of all type 2 OPV (OPV2) use in routine immunization in 2016 but did not successfully end the transmission of type 2 VDPVs (VDPV2s), and consequently continues to use type 2 OPV (OPV2) for outbreak response activities. Using an updated global poliovirus transmission and OPV evolution model, we characterize outbreak response options for 2019-2029 related to responding to VDPV2 outbreaks with a genetically stabilized novel OPV (nOPV2) strain or with the currently licensed monovalent OPV2 (mOPV2). Given uncertainties about the properties of nOPV2, we model different assumptions that appear consistent with the evidence on nOPV2 to date. Using nOPV2 to respond to detected cases may reduce the expected VDPV and VAPP cases and the risk of needing to restart OPV2 use in routine immunization compared to mOPV2 use for outbreak response. The actual properties, availability, and use of nOPV2 will determine its effects on type 2 poliovirus transmission in populations. Even with optimal nOPV2 performance, countries and the GPEI would still likely need to restart OPV2 use in routine immunization in OPV-using countries if operational improvements in outbreak response to stop the transmission of cVDPV2s are not implemented effectively.

Reflections on Modeling Poliovirus Transmission and the Polio Eradication Endgame

The Global Polio Eradication Initiative (GPEI) partners engaged modelers during the past nearly 20 years to support strategy and policy discussions and decisions, and to provide estimates of the risks, costs, and benefits of different options for managing the polio endgame. Limited efforts to date provided insights related to the validation of the models used for GPEI strategy and policy decisions. However, modeling results only influenced decisions in some cases, with other factors carrying more weight in many key decisions. In addition, the results from multiple modeling groups do not always agree, which supports selection of some strategies and/or policies counter to the recommendations from some modelers but not others. This analysis reflects on our modeling, and summarizes our premises and recommendations, the outcomes of these recommendations, and the implications of key limitations of models with respect to polio endgame strategy. We briefly review the current state of the GPEI given epidemiological experience as of early 2020, which includes failure of the GPEI to deliver on the objectives of its 2013-2018 strategic plan despite full financial support. Looking ahead, we provide context for why the GPEI strategy of global oral poliovirus vaccine (OPV) cessation to end all cases of poliomyelitis looks infeasible given the current state of the GPEI and the failure to successfully stop all transmission of serotype 2 live polioviruses within four years of the April-May 2016 coordinated cessation of serotype 2 OPV use in routine immunization.

Vaccine-Derived Poliovirus Infection among Patients with Primary Immunodeficiency and Effect of Patient Screening on Disease Outcomes, Iran

Patients with immunodeficiency-associated vaccine-derived poliovirus (iVDPV) are potential poliovirus reservoirs in the posteradication era that might reintroduce polioviruses into the community. We update the iVDPV registry in Iran by reporting 9 new patients. In addition to national acute flaccid paralysis surveillance, cases were identified by screening nonparalyzed primary immunodeficiency (PID) patients. Overall, 23 iVDPV patients have been identified since 1995. Seven patients (30%) never had paralysis. Poliovirus screening accelerated the iVDPV detection rate in Iran after 2014.The iVDPV infection rate among nonparalyzed patients with adaptive PID was 3.1% (7/224), several folds higher than previous estimates. Severe combined immunodeficiency patients had the highest risk for asymptomatic infection (28.6%) compared with other PIDs. iVDPV2 emergence has decreased after the switch from trivalent to bivalent oral poliovirus vaccine in 2016. However, emergence of iVDPV1 and iVDPV3 continued. Poliovirus screening in PID patients is an essential step in the endgame of polio eradication.

Prevalence of poliovirus vaccine strains in randomized stool samples from 2010 to 2018: encompassing transition from the trivalent to bivalent oral poliovirus vaccine

Global eradication of poliovirus (PV) has previously relied on the live attenuated oral poliovirus vaccine (OPV). However, in order to eliminate the risk of vaccine-associated paralytic poliomyelitis, the use of OPV will soon be discontinued. Thailand has introduced inactivated polio vaccine since December 2015 and replaced trivalent with bivalent OPV since April 2016. To provide crucial surveillance data during this polio vaccine transition period, poliovirus shedding in stool was performed. A total of 7446 stool samples between 2010 and September 2018 were tested for poliovirus using reverse-transcription polymerase chain reaction. Approximately 0.44% (33/7446) of the samples tested were positive for PV. All positive specimens had more than 99% homology with the Sabin vaccine strain, based on complete VP1 nucleotide sequences. Although trivalent OPV use has been discontinued in Thailand since April 2016, PV type 2 could be detected in stool samples collected in May 2016 but has not been found afterwards. The use of bivalent OPV was able to reduce PV type 2 shedding in stools and could contribute to the reduction of vaccine-associated paralytic poliomyelitis in Thai children.

A Review of the Most Commonly Used Methods for Sample Collection in Environmental Surveillance of Poliovirus

We performed a review of the environmental surveillance methods commonly used to collect and concentrate poliovirus (PV) from water samples. We compared the sampling approaches (trap vs grab), the process methods (precipitation vs filtration), and the various tools and chemical reagents used to separate PV from other viruses and pathogens in water samples (microporous glass, pads, polyethylene glycol [PEG]/dextran, PEG/sodium chloride, NanoCeram/ViroCap, and ester membranes). The advantages and disadvantages of each method are considered, and the geographical areas where they are currently used are discussed. Several methods have demonstrated the ability to concentrate and recover PVs from environmental samples. The details of the particular sampling conditions and locations should be considered carefully in method selection.

Enhanced neutralizing antibody response induced by inactivated enterovirus 71 in cynomolgus monkeys

Enterovirus 71 (EV71) is a major etiological agent of various public health issues, particularly in the Asia-Pacific region. EV71 causes hand-foot-and-mouth disease (HFMD) and is associated with serious neurological disorders in young children. A formalin-inactivated EV71 candidate vaccine (KCDC-HFMDV1-EV71) based on the C4 subgenotype was previously developed and confirmed to be a potential candidate vaccine for prevention of EV71 infection in mice. In this study, an inactivated EV71 vaccine was used for analysis of long-term immunogenicity and efficacy in cynomolgus monkeys, a common nonhuman primate model. The vaccine was immunized three times at 0, 4, and 8 weeks with either 20-μg doses of EV71 candidate vaccine formulated with aluminum hydroxide gel adjuvant or phosphate-buffered saline as a control. The group immunized with the inactivated EV71 showed significantly increased EV71-specific antibody and serum neutralizing antibody titers at 3 weeks after vaccination and maintained these elevated titers until the end of the experiment (54 weeks after vaccination). The sera from vaccinated cynomolgus monkeys showed a crossreactive neutralizing antibody response to the heterologous subtype of EV71 (B1–4, C1, and C2). These findings suggest that the inactivated EV71 candidate vaccine may be a potential vaccine candidate and valuable tool for the control of HFMD.

Vaccine-associated paralytic poliomyelitis in the Russian Federation in 1998-2014

OBJECTIVES

Different polio vaccination schemes have been used in Russia: oral polio vaccine (OPV) was used in 1998-2007 and inactivated polio vaccine (IPV) followed by OPV in 2008-2014. This article presents the characteristics of vaccine-associated paralytic poliomyelitis (VAPP) cases in Russia during this period.

METHODS

VAPP cases were identified through the acute flaccid paralysis surveillance system, classified by the National Expert Classification Committee. Criteria for a 'recipient VAPP' (rVAPP) case were poliomyelitis symptoms 6-30days after OPV administration, isolation of the vaccine virus, and residual paralysis 60days after disease onset. Unvaccinated cases with a similar picture 6-60days after contact with an OPV recipient were classified as 'contact VAPP' (cVAPP) cases.

RESULTS

During 1998-2014, 127 VAPP cases were registered: 82 rVAPP and 45 cVAPP. During the period in which only OPV was used, rVAPP cases prevailed (73.8%); cases of rVAPP were reduced during the sequential scheme period (15%). Poliovirus type 3 (39.5%) and type 2 (23.7%) were isolated more often. Vaccine-derived poliovirus types 1, 2, and 3 were isolated from three cases of cVAPP. The incidence of VAPP cases was higher during the period of OPV use (1 case/1.59 million OPV doses) than during the sequential scheme period (1 case/4.18 million doses).

CONCLUSION

The risk of VAPP exists if OPV remains in the vaccination schedule.

Newcastle Disease Virus-Based Vectored Vaccine against Poliomyelitis

The poliovirus eradication initiative has spawned global immunization infrastructure and dramatically decreased the prevalence of the disease, yet the original virus eradication goal has not been met. The suboptimal properties of the existing vaccines are among the major reasons why the program has repeatedly missed eradication deadlines. Oral live poliovirus vaccine (OPV), while affordable and effective, occasionally causes the disease in the primary recipients, and the attenuated viruses rapidly regain virulence and can cause poliomyelitis outbreaks. Inactivated poliovirus vaccine (IPV) is safe but expensive and does not induce the mucosal immunity necessary to interrupt virus transmission. While the need for a better vaccine is widely recognized, current efforts are focused largely on improvements to the OPV or IPV, which are still beset by the fundamental drawbacks of the original products. Here we demonstrate a different design of an antipoliovirus vaccine based on in situ production of virus-like particles (VLPs). The poliovirus capsid protein precursor, together with a protease required for its processing, are expressed from a Newcastle disease virus (NDV) vector, a negative-strand RNA virus with mucosal tropism. In this system, poliovirus VLPs are produced in the cells of vaccine recipients and are presented to their immune systems in the context of active replication of NDV, which serves as a natural adjuvant. Intranasal administration of the vectored vaccine to guinea pigs induced strong neutralizing systemic and mucosal antibody responses. Thus, the vectored poliovirus vaccine combines the affordability and efficiency of a live vaccine with absolute safety, since no full-length poliovirus genome is present at any stage of the vaccine life cycle.IMPORTANCE A new, safe, and effective vaccine against poliovirus is urgently needed not only to complete the eradication of the virus but also to be used in the future to prevent possible virus reemergence in a postpolio world. Currently, new formulations of the oral vaccine, as well as improvements to the inactivated vaccine, are being explored. In this study, we designed a viral vector with mucosal tropism that expresses poliovirus capsid proteins. Thus, poliovirus VLPs are produced in vivo, in the cells of a vaccine recipient, and are presented to the immune system in the context of vector virus replication, stimulating the development of systemic and mucosal immune responses. Such an approach allows the development of an affordable and safe vaccine that does not rely on the full-length poliovirus genome at any stage.

Characterization of human monoclonal antibodies that neutralize multiple poliovirus serotypes

Following the eradication of wild poliovirus (PV), achieving and maintaining a polio-free status will require eliminating potentially pathogenic PV strains derived from the oral attenuated vaccine. For this purpose, a combination of non-cross-resistant drugs, such as small molecules and neutralizing monoclonal antibodies (mAbs), may be ideal. We previously isolated chimpanzee and human mAbs capable of neutralizing multiple PV types (cross-neutralization). Here, we describe three additional human mAbs that neutralize types 1 and 2 PV and one mAb that neutralizes all three types. Most bind conformational epitopes and have unusually long heavy chain complementarity determining 3 domains (HC CDR3). We assessed the ability of the mAbs to neutralize A12 escape mutant PV strains, and found that the neutralizing activities of the mAbs were disrupted by different amino acid substitutions. Competitive binding studies further suggested that the specific mAb:PV interactions that enable cross-neutralization differ among mAbs and serotypes. All of the cloned mAbs bind PV in the vicinity of the "canyon", a circular depression around the 5-fold axis of symmetry through which PV recognizes its cellular receptor. We were unable to generate escape mutants to two of the mAbs, suggesting that their epitopes are important for the PV life cycle. These data indicate that PV cross-neutralization involves binding to highly conserved structures within the canyon that binds to the cellular receptor. These may be facilitated by the long HC CDR3 domains, which may adopt alternative binding configurations. We propose that the human and chimpanzee mAbs described here could have potential as anti-PV therapeutics.

Environmental Surveillance of Polioviruses in Rio de Janeiro, Brazil, in Support to the Activities of Global Polio Eradication Initiative

Wild polioviruses still remain endemic in three countries (Afghanistan, Pakistan, and Nigeria) and re-emergency of wild polio has been reported in previously polio-free countries. Environmental surveillance has been used as a supplementary tool in monitoring the circulation of wild poliovirus (PVs) and/or vaccine-derived PVs even in the absence of acute flaccid paralysis cases. This study aimed to monitor the presence of polioviruses in wastewater samples collected at one wastewater treatment plant located in the municipality of Rio de Janeiro, Brazil. From December 2011 to June 2012 and from September to December 2012, 31 samples were collected and processed. RD and L20B cell cultures were able to isolate PVs and non-polio enteroviruses in 27/31 samples. Polioviruses were isolated in eight samples (type 1 Sabin = 1, type 2 Sabin = 5, and type 3 Sabin = 2). Vaccine-derived polioviruses were not detected nor evidence of recombination with other PVs or non-polio enterovirus serotypes were observed among the isolates. The Sabin-related serotypes 2 and 3 presented nucleotide substitutions in positions associated with the neurovirulent phenotype at the 5'-UTR. Changes in important Amino acid residues at VP1 were also observed in the serotypes 2 and 3. Environmental surveillance has been used successfully in monitoring the circulation of PVs and non-polio enteroviruses and it is of crucial importance in the final stages of the WHO global polio eradication initiative. Our results show the continuous circulation of Sabin-like PVs and non-polio enteroviruses in the analyzed area during the study period.

The Challenge of Global Poliomyelitis Eradication

In the United States during the 1950's, polio was on the forefront of every provider and caregiver's mind. Today, most providers in the United States have never seen a case. The Global Polio Eradication Initiative (GPEI), which began in 1988 has reduced the number of cases by over 99%. The world is closer to achieving global eradication of polio than ever before but as long as poliovirus circulates anywhere in the world, every country is vulnerable. The global community can support the polio eradication effort through continued vaccination, surveillance, enforcing travel regulations and contributing financial support, partnerships and advocacy.

Nucleobase but not Sugar Fidelity is Maintained in the Sabin I RNA-Dependent RNA Polymerase

The Sabin I poliovirus live, attenuated vaccine strain encodes for four amino acid changes (i.e., D53N, Y73H, K250E, and T362I) in the RNA-dependent RNA polymerase (RdRp). We have previously shown that the T362I substitution leads to a lower fidelity RdRp, and viruses encoding this variant are attenuated in a mouse model of poliovirus. Given these results, it was surprising that the nucleotide incorporation rate and nucleobase fidelity of the Sabin I RdRp is similar to that of wild-type enzyme, although the Sabin I RdRp is less selective against nucleotides with modified sugar groups. We suggest that the other Sabin amino acid changes (i.e., D53N, Y73H, K250E) help to re-establish nucleotide incorporation rates and nucleotide discrimination near wild-type levels, which may be a requirement for the propagation of the virus and its efficacy as a vaccine strain. These results also suggest that the nucleobase fidelity of the Sabin I RdRp likely does not contribute to viral attenuation.

Applying the Concept of Peptide Uniqueness to Anti-Polio Vaccination

Background. Although rare, adverse events may associate with anti-poliovirus vaccination thus possibly hampering global polio eradication worldwide. Objective. To design peptide-based anti-polio vaccines exempt from potential cross-reactivity risks and possibly able to reduce rare potential adverse events such as the postvaccine paralytic poliomyelitis due to the tendency of the poliovirus genome to mutate. Methods. Proteins from poliovirus type 1, strain Mahoney, were analyzed for amino acid sequence identity to the human proteome at the pentapeptide level, searching for sequences that (1) have zero percent of identity to human proteins, (2) are potentially endowed with an immunologic potential, and (3) are highly conserved among poliovirus strains. Results. Sequence analyses produced a set of consensus epitopic peptides potentially able to generate specific anti-polio immune responses exempt from cross-reactivity with the human host. Conclusion. Peptide sequences unique to poliovirus proteins and conserved among polio strains might help formulate a specific and universal anti-polio vaccine able to react with multiple viral strains and exempt from the burden of possible cross-reactions with human proteins. As an additional advantage, using a peptide-based vaccine instead of current anti-polio DNA vaccines would eliminate the rare post-polio poliomyelitis cases and other disabling symptoms that may appear following vaccination.

Vaccine-associated paralytic poliomyelitis: a review of the epidemiology and estimation of the global burden

BACKGROUND

Vaccine-associated paralytic poliomyelitis (VAPP) is a rare adverse event associated with oral poliovirus vaccine (OPV). This review summarizes the epidemiology and provides a global burden estimate.

METHODS

A literature review was conducted to abstract the epidemiology and calculate the risk of VAPP. A bootstrap method was applied to calculate global VAPP burden estimates.

RESULTS

Trends in VAPP epidemiology varied by country income level. In the low-income country, the majority of cases occurred in individuals who had received >3 doses of OPV (63%), whereas in middle and high-income countries, most cases occurred in recipients after their first OPV dose or unvaccinated contacts (81%). Using all risk estimates, VAPP risk was 4.7 cases per million births (range, 2.4-9.7), leading to a global annual burden estimate of 498 cases (range, 255-1018). If the analysis is limited to estimates from countries that currently use OPV, the VAPP risk is 3.8 cases per million births (range, 2.9-4.7) and a burden of 399 cases (range, 306-490).

CONCLUSIONS

Because many high-income countries have replaced OPV with inactivated poliovirus vaccine, the VAPP burden is concentrated in lower-income countries. The planned universal introduction of inactivated poliovirus vaccine is likely to substantially decrease the global VAPP burden by 80%-90%.

Transmission dynamics of oral polio vaccine viruses and vaccine-derived polioviruses on networks

One drawback of oral polio vaccine (OPV) is the potential reversion to more transmissible, virulent circulating vaccine-derived polioviruses (cVDPVs), which may cause outbreaks of paralytic poliomyelitis. Previous modeling studies of the transmission of cVDPVs assume an unrealistic homogeneous mixing of the population and/or ignore that OPV viruses and cVDPVs compete for susceptibles, which we show is a key to understanding the dynamics of the transmission of cVDPVs. We examined the transmission of OPV viruses and cVDPVs on heterogeneous, dynamic contact networks using differential equation-based and individual-based models. Despite the lower transmissibility, OPV viruses may outcompete more transmissible cVDPVs in the short run by spreading extensively before cVDPVs emerge. If viruses become endemic, however, cVDPVs eventually dominate and force OPV viruses to extinction. This study improves our understanding of the emergence of cVDPVs and helps develop more detailed models to plan a policy to control paralytic polio associated with the continued use of OPV in many countries.

Limited and localized outbreak of newly emergent type 2 vaccine-derived poliovirus in Sichuan, China

From August 2011 to February 2012, an outbreak caused by type 2 circulating vaccine-derived poliovirus (cVDPV) occurred in Aba County, Sichuan, China. During the outbreak, four type 2 VDPVs (≥0.6% nucleotide divergence in the VP1 region relative to the Sabin 2 strain) were isolated from 3 patients with acute flaccid paralysis (AFP) and one close contact. In addition, a type 2 pre-VDPV (0.3% to 0.5% divergence from Sabin 2) that was genetically related to these type 2 VDPVs was isolated from another AFP patient. These 4 patients were all unimmunized children 0.7 to 1.1 years old. Nucleotide sequencing revealed that the 4 VDPV isolates differed from Sabin 2 by 0.7% to 1.2% in nucleotides in the VP1 region and shared 5 nucleotide substitutions with the pre-VDPV. All 5 isolates were closely related, and all were S2/S3/S2/S3 recombinants sharing common recombination crossover sites. Although the two major determinants of attenuation and temperature sensitivity phenotype of Sabin 2 (A481 in the 5' untranslated region and Ile143 in the VP1 protein) had reverted in all 5 isolates, one VDPV (strain CHN16017) still retained the temperature sensitivity phenotype. Phylogenetic analysis of the third coding position of the complete P1 coding region suggested that the cVDPVs circulated locally for about 7 months following the initiating oral poliovirus vaccine (OPV) dose. Our findings reinforce the point that cVDPVs can emerge and spread in isolated communities with immunity gaps and highlight the emergence risks of type 2 cVDPVs accompanying the trivalent OPV used. To solve this issue, it is recommended that type 2 OPV be removed from the trivalent OPV or that inactivated polio vaccine (IPV) be used instead.

Human monoclonal antibodies that neutralize vaccine and wild-type poliovirus strains

An essential requirement for eradication of poliomyelitis is the elimination of circulating vaccine derived polioviruses (cVDPV) and polioviruses excreted by chronically infected individuals with immunodeficiencies (iVDPV). As part of a post-eradication risk management strategy, a human monoclonal antibody (mAb) therapeutic could play a role in halting excretion in asymptomatic carriers and could be used, in combination with vaccines and antiviral drugs, to protect polio-exposed individuals. Cross-neutralizing mAbs may be particularly useful, as they would reduce the number of mAbs needed to create a comprehensive PV therapeutic. We cloned a panel of IgG mAbs from OPV-vaccinated, IPV-boosted healthy subjects. Many of the mAbs had potent neutralizing activities against PV wild-type (WT) and Sabin strains, and two of the mAbs, 12F8 and 1E4, were significantly cross-reactive against types 1 and 2 and types 1 and 3, respectively. Mapping the binding epitopes using strains resistant to neutralization (escape mutants) suggested that cross-specific PV binding epitopes may primarily reside within the canyon region, which interacts with the cellular receptor molecule CD155 and the cross-neutralizing chimpanzee/human mAb, A12. Despite their close proximity, the epitopes for the 12F8 and 1E4 mAbs on Sabin 1 were not functionally identical to the A12 epitope. When tested together, 12F8 and 1E4 neutralized a diverse panel of clinically relevant PV strains and did not exhibit interference. Virus mutants resistant to the anti-poliovirus drug V-073 were also neutralized by the mAbs. The 12F8 and 1E4 mAbs may suitable for use as anti-PV therapeutics.

Detection of Enteroviruses in Influent and Effluent Flow Samples from Wastewater Treatment Plants in Italy

This study evaluated the presence and seasonal distribution of polio and other enteroviruses in four wastewater treatment plants in three cities in Italy, using different treatment systems. Detection of enteroviruses was carried out by virus isolation in cell cultures after concentration of water samples collected at both inlet and outlet of the treatment plants, following the methods described in the WHO guidelines. Viral serotypes isolated before and after water treatment were compared. Forty-eight non-polio enteroviruses were isolated from 312 samples collected at the inlet of the four wastewater treatment plants, 35 of which were Coxsackievirus type B (72.9 %) and 13 Echovirus (27.1 %). After treatment, 2 CVB3, 1 CVB5, and 1 Echo 6 were isolated. CVB3 and Echo 6 serotypes were also detected in samples collected at the inlet of the TP, in the same month and year. The high rate of detection of infectious enteroviruses in inlet sewage samples (30.1 %) indicates wide diffusion of these viruses in the populations linked to the collectors. The incomplete removal of infectious viruses following sewage treatment highlights possible risks for public health relate to treated waters discharge into the environment.

Evolution and circulation of type-2 vaccine-derived polioviruses in Nad Ali district of Southern Afghanistan during June 2009-February 2011

Oral polio vaccine has been used successfully as a powerful tool to control the spread of wild polioviruses throughout the world; however, during replication in under immunized children, some vaccine viruses revert and acquire the neurovirulent phenotypic properties. In this study, we describe the evolution and circulation of Vaccine-Derived Polioviruses (VDPVs) in Helmand province of Afghanistan. We investigated 2646 AFP cases of Afghan children from June 2009-February 2011 and isolated 103 (04%) vaccine viruses, 45(1.7%) wild type polioviruses and six (0.22%) type 2 circulating vaccine-derived polioviruses (cVDPVs). These cVDPVs showed 97.7%-98.2% nucleotide and 98%-98.7% amino acid homology in VP1 region on comparison with Sabin type 2 reference strain. All these cVDPVs had two signature mutations of neurovirulent phenotypes and 12 additional mutations in P1 capsid region that might also have contributed to increase neurovirulence and replication. Phylogenetic analysis revealed that all these viruses were closely related and originated from previously reported Sabin like 2 virus from Pakistan which did not conform to the standard definition of VDPVs at that time. It was also observed that initial OPV dose was administered approximately 9 months prior to the collection of first stool specimen of index case. Our findings support that suboptimal surveillance and low routine immunization coverage have contributed to the emergence and spread of these viruses in Afghanistan. We therefore recommend high quality immunization campaigns not only in affected district Nad Ali but also in the bordering areas between Pakistan and Afghanistan to prevent the spread of cVDPVs.

Cross-neutralizing human anti-poliovirus antibodies bind the recognition site for cellular receptor

Most structural information about poliovirus interaction with neutralizing antibodies was obtained in the 1980s in studies of mouse monoclonal antibodies. Recently we have isolated a number of human/chimpanzee anti-poliovirus antibodies and demonstrated that one of them, MAb A12, could neutralize polioviruses of both serotypes 1 and 2. This communication presents data on isolation of an additional cross-neutralizing antibody (F12) and identification of a previously unknown epitope on the surface of poliovirus virions. Epitope mapping was performed by sequencing of antibody-resistant mutants and by cryo-EM of complexes of virions with Fab fragments. The results have demonstrated that both cross-neutralizing antibodies bind the site located at the bottom of the canyon surrounding the fivefold axis of symmetry that was previously shown to interact with cellular poliovirus receptor CD155. However, the same antibody binds to serotypes 1 and 2 through different specific interactions. It was also shown to interact with type 3 poliovirus, albeit with about 10-fold lower affinity, insufficient for effective neutralization. Antibody interaction with the binding site of the cellular receptor may explain its broad reactivity and suggest that further screening or antibody engineering could lead to a universal antibody capable of neutralizing all three serotypes of poliovirus.

A quantitative survey of the literature on poliovirus infection and immunity

OBJECTIVE

To examine forces that drive vaccination policy to eradicate wild- and vaccine-derived poliovirus, and to focus on the efficacy of vaccines to support decision-making and further research.

METHODS

We searched PubMed and Ovid databases for English-language publications, without date restrictions. We also collected references from major reviews on polio vaccine immunogenicity or protection. We conducted a meta-analysis of human immunity to polio infections using multiple non-linear regression, and built a database from a broad (but not systematic) set of polio vaccine studies (46 studies, >10000 subjects).

RESULTS

The outcome was an immunological model representative of many different datasets. Parameters measured immunogenicity to both humoral and mucosal immune compartments for Salk and Sabin vaccines. The immunity model was more highly correlated with the data than a simpler per-dose efficacy model.

CONCLUSIONS

The model offers new insights for immunization policy. We measured the mucosal immunogenicity of IPV to a precision that is useful in decision-making for end-game polio immunization policies.

Clinical and enterovirus findings associated with acute flaccid paralysis in the Republic of Korea during the recent decade

Acute flaccid paralysis (AFP) is described as sudden onset of flaccid paralysis in one or more limbs in children caused by polioviruses (PVs). PV eradication is achieved through intensive immunization and AFP attentive surveillance, according to the World Health Organization. Since 1998, the Korea Centers for Disease Control and Prevention has conducted surveillance system. This is an overview of surveillance in the Republic of Korea during the 10-year period from 2002 to 2011. The surveillance system for wild PV eradication was conducted through reporting and laboratory testing. Cell culture isolates were identified by neutralization tests using standard polyclonal antisera typing. The molecular methods were used for further characterization to improve specificity. For genotyping, semi-nested RT-PCR was used to amplify part of the viral protein 1 gene. Patients below 5 years of age accounted for the largest proportion of cases, and a positive association between age and incidence was found. In the total 285 cases, Guillain-Barré syndrome was the major leading causes of AFP. Non-polio enterovirus was detected in some AFP patients. EV71 was detected in 21 cases and Coxsackievirus (C) A2, CA6, CA9, CB2, CB3, CB4, CB5, and Echovirus (E) 25, E30, Sabin strain polio 2, polio 1 and 3 were also detected in some patients. The present study represents a comprehensive 10-year country-based survey of AFP in the Republic of Korea. This surveillance could provide better understanding of the epidemiologic pattern, and clinical manifestations associated with specific genotypes of AFP in the Republic of Korea.

Risks associated with the use of live-attenuated vaccine poliovirus strains and the strategies for control and eradication of paralytic poliomyelitis

The Global Polio Eradication Initiative was launched in 1988 with the aim to eliminate paralytic poliomyelitis. Two effective vaccines are available: inactivated polio vaccine (IPV) and oral polio vaccine (OPV). Since 1964, OPV has been used instead of IPV in most countries due to several economic and biological advantages. However, in rare cases, the live-attenuated Sabin strains of OPV revert to neurovirulence and cause vaccine-associated paralytic poliomyelitis in vaccinees or lead to emergence of vaccine-derived poliovirus strains. Attenuating mutations and recombination events have been associated with the reversion of vaccine strains to neurovirulence. The substitution of OPV with an improved new-generation IPV and the availability of new specific drugs against polioviruses are considered as future strategies for outbreak control and the eradication of paralytic poliomyelitis worldwide.

Role of environmental poliovirus surveillance in global polio eradication and beyond

Environmental poliovirus surveillance (ENV) means monitoring of poliovirus (PV) transmission in human populations by examining environmental specimens supposedly contaminated by human faeces. The rationale is based on the fact that PV-infected individuals, whether presenting with disease symptoms or not, shed large amounts of PV in the faeces for several weeks. As the morbidity:infection ratio of PV infection is very low, this fact contributes to the sensitivity of ENV which under optimal conditions can be better than that of the standard acute flaccid paralysis (AFP) surveillance. The World Health Organization has included ENV in the new Strategic Plan of the Global Polio Eradication Initiative for years 2010–2012 to be increasingly used in PV surveillance, supplementing AFP surveillance. In this paper we review the feasibility of using ENV to monitor wild PV and vaccine-derived PV circulation in human populations, based on global experiences in defined epidemiological situations.

Paralytic poliomyelitis associated with Sabin monovalent and bivalent oral polio vaccines in Hungary

Historical records of patients with vaccine-associated paralytic poliomyelitis (VAPP) in Hungary during 1961-1981 were reviewed to assess the risk of VAPP after oral polio vaccine (OPV) administration. A confirmed VAPP case was defined as a diagnosis of paralytic poliomyelitis and residual paralysis at 60 days in a patient with an epidemiologic link to the vaccine. Archived poliovirus isolates were retested using polymerase chain reaction and sequencing of the viral protein 1 capsid region. This review confirmed 46 of 47 cases previously reported as VAPP. Three cases originally linked to monovalent OPV (mOPV) 3 and one case linked to mOPV1 presented after administration of bivalent OPV 1 + 3 (bOPV). The adjusted VAPP risk per million doses administered was 0.18 for mOPV1 (2 cases/11.13 million doses), 2.96 for mOPV3 (32 cases/10.81 million doses), and 12.82 for bOPV (5 cases/390,000 doses). Absence of protection from immunization with inactivated poliovirus vaccine or exposure to OPV virus from routine immunization and recent injections could explain the higher relative risk of VAPP in Hungarian children. In polio-endemic areas in which mOPV3 and bOPV are needed to achieve eradication, the higher risk of VAPP would be offset by the high risk of paralysis due to wild poliovirus and higher per-dose efficacy of mOPV3 and bOPV compared with trivalent OPV.

Chimpanzee-human monoclonal antibodies for treatment of chronic poliovirus excretors and emergency postexposure prophylaxis

Six poliovirus-neutralizing Fabs were recovered from a combinatorial Fab phage display library constructed from bone marrow-derived lymphocytes of immunized chimpanzees. The chimeric chimpanzee-human full-length IgGs (hereinafter called monoclonal antibodies [MAbs]) were generated by combining a chimpanzee IgG light chain and a variable domain of heavy chain with a human constant Fc region. The six MAbs neutralized vaccine strains and virulent strains of poliovirus. Five MAbs were serotype specific, while one MAb cross-neutralized serotypes 1 and 2. Epitope mapping performed by selecting and sequencing antibody-resistant viral variants indicated that the cross-neutralizing MAb bound between antigenic sites 1 and 2, thereby covering the canyon region containing the receptor-binding site. Another serotype 1-specific MAb recognized a region located between antigenic sites 2 and 3 that included parts of capsid proteins VP1 and VP3. Both serotype 2-specific antibodies recognized antigenic site 1. No escape mutants to serotype 3-specific MAbs could be generated. The administration of a serotype 1-specific MAb to transgenic mice susceptible to poliovirus at a dose of 5 μg/mouse completely protected them from paralysis after challenge with a lethal dose of wild-type poliovirus. Moreover, MAb injection 6 or 12 h after virus infection provided significant protection. The MAbs described here could be tested in clinical trials to determine whether they might be useful for treatment of immunocompromised chronic virus excretors and for emergency protection of contacts of a paralytic poliomyelitis case.

Mechanisms of genetic variation in polioviruses

Polioviruses, as with all RNA viruses, are in a constant process of evolution driven by different mechanisms. With multiple mechanisms for genetic variability, they are successful conformists, adapting to changes in their habitat. The evolution of polioviruses may occur with generation of point mutations followed by genetic drift and selection. The mutation rate of polioviruses based on several studies is approximately 3 × 10(-2) mutations/synonymous site/year in the gene encoding viral protein 1. Genetic variation in polioviruses may also be increased by sharing of genetic data of two different poliovirus lineages by means of homologous recombination. According to the current view, recombination is considered usually to occur by strand-switching, but a non-replicative model has also been described. In recombination, polioviruses may either gain a set of advantageous mutations selected and fixed in previous generations of the parental viruses or get rid of deleterious ones. The prerequisites and constraints of the evolution mechanisms will be discussed. Furthermore, consequences of poliovirus evolution will be reviewed in the light of observations made on currently circulating polioviruses. We will also describe how polioviruses strike back: as wild type polioviruses approach eradication, vaccine derived strains increase their occurrence and genetic variability.

Enterovirus infections of the central nervous system

Enteroviruses (EV) frequently infect the central nervous system (CNS) and induce neurological diseases. Although the CNS is composed of many different cell types, the spectrum of tropism for each EV is considerable. These viruses have the ability to completely shut down host translational machinery and are considered highly cytolytic, thereby causing cytopathic effects. Hence, CNS dysfunction following EV infection of neuronal or glial cells might be expected. Perhaps unexpectedly given their cytolytic nature, EVs may establish a persistent infection within the CNS, and the lasting effects on the host might be significant with unanticipated consequences. This review will describe the clinical aspects of EV-mediated disease, mechanisms of disease, determinants of tropism, immune activation within the CNS, and potential treatment regimes.

Testing clinical surveillance of acute flaccid paralysis in Egypt post-eradication of poliomyelitis

OBJECTIVE

To assess the knowledge of polio detection and notification by front-line clinicians in Egypt.

METHODS

This study examines clinicians' knowledge and awareness of polio detection and notification using a multiple-choice questionnaire (maximum score=43) in three large health care centres in central Cairo (n=52).

RESULTS

The results reveal a significant variation of knowledge amongst doctors, with junior and senior house officers scoring an average of 30.6 (95% CI: 29.5-31.7), specialist registrars and consultant paediatricians 30.3 (CI 28.9-31.7), and public health doctors 35.4 (CI 32.9-36.8). Mean total scores of public health doctors were significantly higher than those of other clinicians. Senior paediatricians performed no better than newly qualified doctors.

CONCLUSIONS

The results suggest that there is a need for more clinical teaching and training amongst junior doctors as well as senior clinicians and consultants. Appropriate knowledge of diagnosing AFP and of the correct protocol amongst clinicians is essential to maintain the high quality of the WHO programme in Egypt.