Vaccine policy changes and epidemiology of poliomyelitis in the United States

Vaccination strategies against wild poliomyelitis in polio-free settings: outbreak risk modelling study and cost-effectiveness analysis

The 2021 importation of wild poliovirus serotype 1 (WPV1) into Malawi with subsequent international spread represented the first WPV1 cases in Africa since 2016. Preventing importations and spread of WPV1 is critical and dependent on population immunity provided through routine immunisation (RI) and supplementary immunisation activities (SIAs). We aim to estimate outbreak risk and costs, given the importation of WPV1 for non-endemic countries in the WHO Africa region. We developed a stochastic mathematical model of polio transmission dynamics to evaluate the probability of an outbreak, expected number of poliomyelitis cases, costs and incremental cost-effectiveness ratios under different vaccination strategies. Across variable RI coverage, we explore three key strategies: RI+outbreak SIAs (oSIAs), RI+oSIAs+annual preventative SIAs (pSIAs) and RI+oSIAs+biennial pSIAs. Results are presented in 2023 USD over a 5year- time horizon from the Global Polio Eradication Initiative (GPEI) and health system perspectives. The annual pSIA strategy has the greatest probability of no outbreaks in comparison to other strategies: under our model assumptions, annual pSIAs result in an 80% probability of no outbreaks when RI coverage is ≥50%. The biennial pSIA strategy requires RI coverage ≥65% to achieve an equivalent risk of no outbreaks. The strategy with no pSIAs requires ≥75% RI coverage to achieve an equivalent risk of no outbreaks. For the health system, when RI coverage is between 35% and 60%, both pSIA strategies are cost-saving. For the GPEI, below 65% RI pSIA strategies are cost-effective, but the biennial pSIA strategy incurs higher costs in comparison to annual pSIAs due to more oSIAs required to stop outbreaks. Prioritisation of pSIAs must balance outbreak risk against implementation costs, ideally favouring the smallest manageable outbreak risk compatible with elimination. We infer that there are few short-term risks due to population immunity from RI, but without pSIAs, long-term risks accumulate and can result in outbreaks with the potential for international spread.

Immunodeficiency-Related Vaccine-Derived Poliovirus (iVDPV) Infections: A Review of Epidemiology and Progress in Detection and Management

Individuals with certain primary immunodeficiency disorders (PID) may be unable to clear poliovirus infection after exposure to oral poliovirus vaccine (OPV). Over time, vaccine-related strains can revert to immunodeficiency-associated vaccine-derived poliovirus (iVDPVs) that can cause paralysis in the patient and potentially spread in communities with low immunity. We reviewed the efforts for detection and management of PID patients with iVDPV infections and the epidemiology through an analysis of 184 cases reported to the World Health Organization (WHO) during 1962-2024 and a review of polio program and literature reports. Most iVDPV patients (79%) reported in the WHO Registry were residents in middle-income countries and almost half (48%) in the Eastern Mediterranean Region. Type 2 iVDPV was most frequently isolated (53%), but a sharp decline was observed after the switch to bivalent OPV in 2016, with only six cases reported during 2017-2024 compared to 63 during 2009-2016. Patients with common variable immunodeficiency have longer excretion of iVDPV than with other PID types. Implementation of sensitive sentinel surveillance to detect cases of iVDPV infection in high-risk countries and offer antiviral treatment to patients is challenged by competition with other health priorities and regulatory hurdles to the compassionate use of investigational antiviral drugs.

[Problems of poliomyelitis eradication]

The article is devoted to the problems of implementation of the WHO Global Polio Eradication Initiative. The influence of the features of poliovirus infection and poliovirus vaccines on the course of the program, its successes and difficulties is considered, the issue of possibility of eradication this infection is discussed.

Immunogenicity evaluation of primary polio vaccination schedule with inactivated poliovirus vaccines and bivalent oral poliovirus vaccine

BACKGROUND

To assess the immunogenicity of the current primary polio vaccination schedule in China and compare it with alternative schedules using Sabin or Salk-strain IPV (sIPV, wIPV).

METHODS

A cross-sectional investigation was conducted at four sites in Chongqing, China, healthy infants aged 60-89 days were conveniently recruited and divided into four groups according to their received primary polio vaccination schedules (2sIPV + bOPV, 2wIPV + bOPV, 3sIPV, and 3wIPV). The sero-protection and neutralizing antibody titers against poliovirus serotypes (type 1, 2, and 3) were compared after the last dose.

RESULTS

There were 408 infants completed the protocol. The observed seropositivity was more than 96% against poliovirus types 1, 2, and 3 in all groups. IPV-only groups induced higher antibody titers(GMT) against poliovirus type 2 (Median:192, QR: 96-384, P<0.05) than the "2IPV + bOPV" group. While the "2IPV + bOPV" group induced significantly higher antibody titers against poliovirus type 1 (Median:2048, QR: 768-2048, P<0.05)and type 3 (Median:2048, QR: 512-2048, P<0.05) than the IPV-only group.

CONCLUSIONS

Our findings have proved that the two doses of IPV with one dose of bOPV is currently the best polio routine immunization schedule in China.

Is it time to switch to a formulation other than the live attenuated poliovirus vaccine to prevent poliomyelitis?

The polioviruses (PVs) are mainly transmitted by direct contact with an infected person through the fecal-oral route and respiratory secretions (or more rarely via contaminated water or food) and have a primary tropism for the gut. After their replication in the gut, in rare cases (far less than 1% of the infected individuals), PVs can spread to the central nervous system leading to flaccid paralysis, which can result in respiratory paralysis and death. By the middle of the 20th century, every year the wild polioviruses (WPVs) are supposed to have killed or paralyzed over half a million people. The introduction of the oral poliovirus vaccines (OPVs) through mass vaccination campaigns (combined with better application of hygiene measures), was a success story which enabled the World Health Organization (WHO) to set the global eradication of poliomyelitis as an objective. However this strategy of viral eradication has its limits as the majority of poliomyelitis cases today arise in individuals infected with circulating vaccine-derived polioviruses (cVDPVs) which regain pathogenicity following reversion or recombination. In recent years (between January 2018 and May 2023), the WHO recorded 8.8 times more cases of polio which were linked to the attenuated OPV vaccines (3,442 polio cases after reversion or recombination events) than cases linked to a WPV (390 cases). Recent knowledge of the evolution of RNA viruses and the exchange of genetic material among biological entities of the intestinal microbiota, call for a reassessment of the polio eradication vaccine strategies.

Immune persistence of an inactivated poliovirus vaccine derived from the Sabin strain: a 10-year follow-up of a phase 3 study

Background

In a previous phase 3 clinical trial, we showed that an inactivated poliovirus vaccine derived from the Sabin strain (sIPV) can induce neutralising antibodies against currently circulating and reference wild poliovirus strains. However, the immune persistence of sIPV remains to be evaluated.

Methods

In this study, 400 participants who were eligible for an early phase 3 clinical trial (Jan 1, 2012-Aug 31, 2014) in Pingle County, GuanXi Province, China, were initially involved in one site. Of the participants in the previous phase 3 clinical trial, sera of 287, 262, 237, and 207 participants were sampled at the ages of 4, 6, 8, and 10 years, respectively, after the prime-boost regimen. Neutralising antibodies against attenuated Sabin strains were detected using these serum samples to determine immune persistence. The serum neutralising antibodies titre of 1:8 against poliovirus types 1, 2, and 3 is considered to be a seroprotection level for polio. The trial is registered at ClinicalTrials.gov, NCT01510366.

Findings

The protective rates against poliovirus types 1, 2, and 3 in the sIPV group were all 100% at 10 years after the booster immunisation, compared with 98.1%, 100%, and 97.1%, respectively, in the wIPV control group after 10 years. After the booster at 18 months, the geometric mean titres (GMTs) of neutralising antibodies against poliovirus types 1, 2, and 3 in the sIPV group were 13,265.6, 7856.7, and 6432.2, respectively, and the GMTs in the control group (inoculated with inactivated poliovirus vaccine derived from wild strain (wIPV)) were 3915.6, 2842.6, and 4982.7, respectively. With increasing time after booster immunisation, the GMTs of neutralising antibodies against poliovirus types 1, 2, and 3 gradually decreased in both the sIPV and wIPV groups. At the age of ten years, the GMTs of neutralising antibodies against poliovirus types 1, 2, and 3 in the sIPV group were 452.3, 392.8, and 347.5, respectively, and the GMTs in the wIPV group 108.5, 154.8, and 229.3, respectively, which were still at a higher-than-protective level (1:8).

Interpretation

Both sIPV and wIPV maintained sufficiently high immune persistence against poliovirus types 1, 2, and 3 for at least 10 years after booster immunisation.

Funding

Yunnan Provincial Science and Technology Department, the Bill and Melinda Gates Foundation, the National High-tech Research and Development Program, the National International Science and Technology Cooperation Project, the Yunnan Application Basic Research Project, the Innovation Team Project of Xie He, the Yunnan International Scientific and Technological Cooperation Project, and the Medical and Technology Innovation Project of Xie He.

A novel tool to eradicate an ancient scourge: the novel oral polio vaccine type 2 story

The recent detection of vaccine-derived poliovirus (VDPV) in London (UK) and a case of paralytic polio in New York (USA) have highlighted how the scourge of poliomyelitis has not been totally overcome and remains an international problem, not confined to Afghanistan and Pakistan (where wild-type 1 poliovirus remains endemic) or as outbreaks of circulating VDPV in countries in Africa. To address the risk of circulating VDPVs, a global collaborative effort over the past decade has enabled the development of novel oral polio vaccine type 2 (nOPV2) that is as immunogenic as the current Sabin strain and so equally effective, while being less likely to revert to neurovirulence than Sabin oral polio vaccines. The successful development of nOPV2-the first such vaccine against type 2 poliovirus and the first vaccine ever authorised by the WHO Prequalification team through its Emergency Use Listing procedure-has led to the deployment of approximately 450 million doses of nOPV2 for outbreak control in 21 countries. It also paved the way for the subsequent Emergency Use Listing approval of COVID-19 vaccines in the global pandemic. Monitoring the use of nOPV2 has confirmed it is more genetically stable and less likely to result in VDPV than the Sabin strain, suggesting that the target of the global eradication of poliomyelitis might be a little more attainable than previously believed.

Molecular evolution and antigenic drift of type 3 iVDPVs excreted from a patient with immunodeficiency in Ningxia, China

A 2.5-year-old pediatric patient with acute flaccid paralysis was diagnosed with primary immunodeficiency (PID) in Ningxia Province, China, in 2011. Twelve consecutive stool specimens were collected from the patient over a period of 10 months (18 February 2011 to 20 November 2011), and 12 immunodeficiency vaccine-derived poliovirus (iVDPV) strains (CHN15017-1 to CHN15017-12) were subsequently isolated. Nucleotide sequencing analysis of the plaque-purified iVDPVs revealed 2%-3.5% VP1-region differences from their parental Sabin 3 strain. Full-length genome sequencing showed they were all Sabin 3/Sabin 1 recombinants, sharing a common 2C-region crossover site, and the two key determinants of attenuation (U472C in the 5' untranslated region and T2493C in the VP1 region) had reverted. Temperature-sensitive experiments demonstrated that the first two iVDPV strains partially retained the temperature-sensitive phenotype's nature, while the subsequent ten iVDPV strains distinctly lost it, possibly associated with increased neurovirulence. Nineteen amino-acid substitutions were detected between 12 iVDPVs and the parental Sabin strain, of which only one (K1419R) was found on the subsequent 10 iVDPV isolates, suggesting this site's potential as a temperature-sensitive determination site. A Bayesian Monte Carlo Markov Chain phylogenetic analysis based on the P1 coding region yielded a mean iVDPV evolutionary rate of 1.02 × 10^-2 total substitutions/site/year, and the initial oral-polio-vaccine dose was presumably administered around June 2009. Our findings provide valuable information regarding the genetic structure, high-temperature growth sensitivity, and antigenic properties of iVDPVs following long-term evolution in a single PID patient, thus augmenting the currently limited knowledge regarding the dynamic changes and evolutionary pathway of iVDPV populations with PID during long-term global replication.

Cost-effectiveness of various immunization schedules with inactivated Sabin strain polio vaccine in Hangzhou, China

Background

It is necessary to select suitable inactivated poliovirus vaccine(IPV) and live, attenuated oral poliovirus vaccine (OPV) sequential immunization programs and configure the corresponding health resources. An economic evaluation was conducted on the sequential procedures of Sabin strain-based IPV (sIPV) and bivalent OPV (bOPV) with different doses to verify whether a cost-effectiveness target can be achieved. This study aimed to evaluate the cost-effectiveness of different sIPV immunization schedules, which would provide convincing evidence to further change the poliovirus vaccine (PV) immunization strategies in China.

Methods

Five strategies were included in this analysis. Based on Strategy 0(S₀), the incremental cost (IC), incremental effect (IE), and incremental cost-effectiveness ratio (ICER) of the four different strategies (S₁/S₂/S₃/S₄) were calculated based on the perspective of the society. Seven cost items were included in this study. Results of field investigations and expert consultations were used to calculate these costs.

Results

The ICs of S₁/S₂/S₃/S₄ was Chinese Yuan (CNY) 30.77, 68.58, 103.82, and 219.82 million, respectively. The IE of vaccine-associated paralytic poliomyelitis (IE_VAPP) cases of S₁/S₂/S₃/S₄ were 0.22, 0.22, 0.22, and 0.11, respectively, while the IE of disability-adjusted life-years (IE_DALY) of S₁/S₂/S₃/S₄ were 8.98, 8.98, 8.98, and 4.49, respectively. The ICER_VAPP of S₁/S₂/S₃/S₄ gradually increased to CNY 13.99, 31.17, 47.19, and 199.83 million/VAPP, respectively. The ICER_DALY of S₁/S₂/S₃/S₄ also gradually increased to CNY 0.34, 0.76, 1.16, and 4.90 million/DALY, respectively.

Conclusion

ICER_VAPP and ICER_DALY were substantially higher for S₃ (four-sIPV) and S₄ (replacement of self-funded sIPV based on one-sIPV-three-bOPV). Two-sIPV-two-bOPV had a cost-effectiveness advantage, whereas S2/S3/S4 had no cost-effectiveness advantage.

Immunity to enteric viruses

Pathogenic enteric viruses are a major cause of morbidity and mortality, particularly among children in developing countries. The host response to enteric viruses occurs primarily within the mucosa, where the intestinal immune system must balance protection against pathogens with tissue protection and tolerance to harmless commensal bacteria and food. Here, we summarize current knowledge in natural immunity to enteric viruses, highlighting specialized features of the intestinal immune system. We further discuss how knowledge of intestinal anti-viral mechanisms can be translated into vaccine development with particular focus on immunization in the oral route. Research reveals that the intestine is a complex interface between enteric viruses and the host where environmental factors influence susceptibility and immunity to infection, while viral infections can have lasting implications for host health. A deeper mechanistic understanding of enteric anti-viral immunity with this broader context can ultimately lead to better vaccines for existing and emerging viruses.

Infectious Diseases-Related Hospitalizations During Oral Polio Vaccine(OPV) and non-OPV immunization periods: An Empirical Evaluation of all Hospital Discharges in California(1985-2010)

BACKGROUND

Live attenuated vaccines such as oral polio vaccine (OPV) can stimulate innate immunity and may have off-target protective effects on other pathogens. We aimed to address this hypothesis by examining changes in infectious diseases (ID)-related hospitalizations in all hospital discharges in California during OPV-(1985-1996) and non-OPV-immunization periods (2000-2010).

METHODS

We searched the OSHPD (Office of Statewide Health Planning and Development) database for all hospital discharges with any ID-related discharge diagnosis code during 1985-2010. We compared the proportion of ID-related hospitalizations (with at least one ID-related discharge diagnosis) among total hospitalizations during OPV immunization (1985-1996) vs non-OPV immunization (2000-2010) periods.

RESULTS

There were 19,281,039 ID-related hospitalizations (8,464,037 with an ID-related discharge-diagnosis as the principal discharge diagnosis for the hospitalization) among 98,117,475 hospitalizations in 1985-2010; 9,520,810 ID-hospitalizations/43,456,484 total hospitalizations in 2000-2010 vs 7,526,957/43,472,796 in 1985-1996. The RR for ID-related hospitalizations in 2000-2010 vs 1985-1996 was 1.27(95% CI: 1.26-1.27) for all diagnoses and 1.15(95% CI: 1.15-1.16) for principal diagnoses. Increases also existed in the proportion of lower respiratory and gastrointestinal infections.

DISCUSSION

The proportion of ID-related hospitalizations was lower in the OPV-immunization period compared to the period after OPV was discontinued. When focused only on hospitalizations with ID as the principal discharge diagnosis the signal remained significant but was smaller. These findings require replication in additional studies.

Cost-Effectiveness of Three Poliovirus Immunization Schedules in Shanghai, China

In Shanghai, China, a polio immunization schedule of four inactivated polio vaccines (IPV) has been implemented since 2020, replacing the schedules of a combination of two IPVs and two bivalent live attenuated oral polio vaccines (bOPV), and four trivalent live attenuated oral polio vaccines (tOPV). This study aimed to assess the cost-effectiveness of these three schedules in infants born in 2016, in preventing vaccine-associated paralytic poliomyelitis (VAPP). We performed a decision tree model and estimated incremental cost-effectiveness ratio (ICER). Compared to the four-tOPV schedule, the two-IPV-two-bOPV schedule averted 1.2 VAPP cases and 16.83 disability-adjusted life years (DALY) annually; while the four-IPV schedule averted 1.35 VAPP cases and 18.96 DALY annually. Consequently, ICER_VAPP and ICER_DALY were substantially high for two-IPV-two-bOPV (CNY 12.96 million and 0.93 million), and four-IPV (CNY 21.24 million and 1.52 million). Moreover, net monetary benefit of the two-IPV-two-bOPV and four-IPV schedules was highest when the cost of IPV was hypothesized to be less than CNY 23.75 or CNY 9.11, respectively, and willingness-to-pay was hypothesized as CNY 0.6 million in averting one VAPP-induced DALY. IPV-containing schedules are currently cost-ineffective in Shanghai. They may be cost-effective by reducing the prices of IPV, which may accelerate polio eradication in Chinese settings.

Advancements in protein nanoparticle vaccine platforms to combat infectious disease

Infectious diseases are a major threat to global human health, yet prophylactic treatment options can be limited, as safe and efficacious vaccines exist only for a fraction of all diseases. Notably, devastating diseases such as acquired immunodeficiency syndrome (AIDS) and coronavirus disease of 2019 (COVID-19) currently do not have vaccine therapies. Conventional vaccine platforms, such as live attenuated vaccines and whole inactivated vaccines, can be difficult to manufacture, may cause severe side effects, and can potentially induce severe infection. Subunit vaccines carry far fewer safety concerns due to their inability to cause vaccine-based infections. The applicability of protein nanoparticles (NPs) as vaccine scaffolds is promising to prevent infectious diseases, and they have been explored for a number of viral, bacterial, fungal, and parasitic diseases. Many types of protein NPs exist, including self-assembling NPs, bacteriophage-derived NPs, plant virus-derived NPs, and human virus-based vectors, and these particular categories will be covered in this review. These vaccines can elicit strong humoral and cellular immune responses against specific pathogens, as well as provide protection against infection in a number of animal models. Furthermore, published clinical trials demonstrate the promise of applying these NP vaccine platforms, which include bacteriophage-derived NPs, in addition to multiple viral vectors that are currently used in the clinic. The continued investigations of protein NP vaccine platforms are critical to generate safer alternatives to current vaccines, advance vaccines for diseases that currently lack effective prophylactic therapies, and prepare for the rapid development of new vaccines against emerging infectious diseases. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

The Current State: Epidemiology and Working Toward Eradication

Acute polio, once epidemic and a significant source of paralysis and disability, has been dramatically reduced through global vaccination programs. Although vaccination efforts have experienced a setback because of COVID-19, resulting in increased number of vaccine-associated and wild virus infections, polio eradication is still a realistic goal that will result in significant cost savings. The secondary health issues related to aging with the residual effects of polio, including postpolio syndrome, will persist for many years posteradication. Continued education of medical professionals is essential to ensure provision of the necessary care to this population.

Prospects for mucosal vaccine: shutting the door on SARS-CoV-2

The sudden emergence of a highly transmissible and pathogenic coronavirus SARS-CoV-2 in December 2019 from China and its rapid global spread has posed an international health emergency. The rapid development of an effective vaccine is imperative to control the spread of SARS-CoV-2. A number of concurrent efforts to find an effective therapeutic agent or vaccine for COVID-19 (coronavirus disease 2019) are being undertaken globally. Oral and nasal mucosal surfaces serve as the primary portal of entry for pathogens like coronaviruses in the human body. As evidenced by studies on similar coronaviruses (SARS-CoV and MERS-CoV), mucosal vaccination can provide a safe and effective means for the induction of long-lasting systemic and mucosal immunity to confer protection against SARS-CoV-2. This article summarizes the approaches to an effective mucosal vaccine formulation which can be a rewarding approach to combat the unprecedented threat posed by this emerging global pandemic.

[Development of inactivated cultural yellow fever vaccine]

INTRODUCTION

The only currently available live vaccine against yellow fever (YF) based on chicken embryos infected with an attenuated 17D strain of the YF virus is one of the most effective vaccine preparations. However, the live vaccine is associated with "viscerotropic syndrome" (approximately 0.4 cases per 100 000 vaccinated). Therefore, the development and introduction of highly purified inactivated vaccine against YF is intended to ensure the maximum safety of vaccination against one of the most common human viral diseases.Goals and objectives. Development and evaluation of immunogenicity of the cultural inactivated vaccine against YF at the laboratory model level.

MATERIAL AND METHODS

Adaptation of 17D strain of YF virus to Vero cell culture, cultivation, removal of cellular DNA, inactivation with β-propiolactone, concentration, chromatographic purification, determination of protein and antigen of YF virus, assessment of immunogenicity in mice in parallel with commercial live vaccine.

RESULTS AND DISCUSSION

Immunogenicity: the determination of specific antibodies of class G (IgG) and virus neutralizing antibodies in the sera of immunized mice showed high level of antibodies exceeding that of immunized with commercial live vaccine. The optimal dose of antigen in the vaccine (total protein) was 50 μg/ml (5 μg/0.1 ml -dose and volume per 1 vaccination of mice). Thus, the laboratory version of cultural inactivated vaccine against YF is as effective (and even superior) as the commercial live vaccine.

CONCLUSION

Laboratory version of cultural inactivated vaccine against YF, which is not inferior in immunogenicity (in animal model) to commercial live vaccine, has been developed.

Sero-survey of polio antibodies and quality of acute flaccid paralysis surveillance in Chongqing, China: A cross-sectional study

Serums were collected from people to assess whether polio immunity level was high enough to satisfy the polio vaccine immunization switch in Chongqing.People in 7 age groups (<1 year, 1-2 years, 3-4 years, 5-6 years, 7-14 years, 15-19 years, ≧20 years) were randomly selected in 3 areas by different geographical features in 2015. Peripheral venous blood samples were obtained and assays to detect poliovirus (PV) -neutralizing antibodies were performed. Acute flaccid paralysis (AFP) data was collected from 2012 to 2016 in Chongqing to evaluate the performance of AFP surveillance system by indicator analysis.A total of 636 people were tested for PV neutralization antibodies (NA). Overall NA seroprevalence for PV1, PV2 and PV3 were 93.40%, 96.38% and 91.82%, and geometric mean titers (GMTs) were 61.14, 66.78 and 21.47, respectively. GMTs and NA seroprevalence for PV1, PV2 and PV3 in older people were lower than young people. There were significant differences in seroprevalences of PV1 and PV3 among geographic areas (P < .05) in Chongqing.High seroprevalence for PV1, PV2, and PV3 and qualified capability for monitoring AFP cases showed that the polio eradication program has made positive achievements in Chongqing and established a stable base for a polio vaccine immunization switch. Nevertheless, GMTs were negatively associated with age in the geographic districts with poor economical features, which will increase the risk of emergence of vaccine-derived PV after polio vaccine switch. More than 1 dose of inactivated polio vaccine should be introduced into the polio vaccine schedule, and the supplementary immunization of polio should still be annually carried out after polio vaccine switch, especially among elder children and the adults.

[Recommendations on the approach when unusual neurological symptoms occur in temporal association with vaccinations in childhood and adolescence]

Vaccinations are often administered at an age when many neurological diseases of childhood and adolescence also occur. Febrile seizures may occur following vaccination in patients with an appropriate genetic predisposition. The occurrence of narcolepsy has been described more frequently after pandemic influenza A-H1N1 vaccinations. The causality has not been proven. Data regarding an association between Guillain-Barré syndrome and influenza vaccinations are inconclusive. It was conclusively shown that vaccinations do not cause neurological disorders, such as autism and do not trigger multiple sclerosis. In summary, there is currently no confirmed evidence for the occurrence of chronic neurological diseases as a consequence of generally recommended vaccinations in Germany. If unusual neurological symptoms are observed in temporal association with vaccinations, a comprehensive evaluation is necessary to exclude a causal relationship and to diagnose the underlying neurological disease independent of the vaccination. This statement gives specific recommendations for the practical approach when neurological symptoms are observed in temporal association with vaccinations with respect to taking the patient history, initial diagnostic procedures, accurate and prompt documentation and the obligation to report the event. The committee also proposes procedures for further clarification and differential diagnostics of causal neurological diseases in childhood and adolescence.

Development of a new oral poliovirus vaccine for the eradication end game using codon deoptimization

Enormous progress has been made in global efforts to eradicate poliovirus, using live-attenuated Sabin oral poliovirus vaccine (OPV). However, as the incidence of disease due to wild poliovirus has declined, vaccine-derived poliovirus (VDPV) has emerged in areas of low-vaccine coverage. Coordinated global cessation of routine, type 2 Sabin OPV (OPV2) use has not resulted in fewer VDPV outbreaks, and continued OPV use in outbreak-response campaigns has seeded new emergences in low-coverage areas. The limitations of existing vaccines and current eradication challenges warranted development of more genetically stable OPV strains, most urgently for OPV2. Here, we report using codon deoptimization to further attenuate Sabin OPV2 by changing preferred codons across the capsid to non-preferred, synonymous codons. Additional modifications to the 5′ untranslated region stabilized known virulence determinants. Testing of this codon-deoptimized new OPV2 candidate (nOPV2-CD) in cell and animal models demonstrated that nOPV2-CD is highly attenuated, grows sufficiently for vaccine manufacture, is antigenically indistinguishable from Sabin OPV2, induces neutralizing antibodies as effectively as Sabin OPV2, and unlike Sabin OPV2 is genetically stable and maintains an attenuation phenotype. In-human clinical trials of nOPV2-CD are ongoing, with potential for nOPV strains to serve as critical vaccine tools for achieving and maintaining polio eradication.

Successful Vaccines

Vaccines are considered one of the most important advances in modern medicine and have greatly improved our quality of life by reducing or eliminating many serious infectious diseases. Successful vaccines have been developed against many of the most common human pathogens, and this success has not been dependent upon any one specific class of vaccine since subunit vaccines, non-replicating whole-virus or whole-bacteria vaccines, and attenuated live vaccines have all been effective for particular vaccine targets. After completing the initial immunization series, one common aspect of successful vaccines is that they induce long-term protective immunity. In contrast, several partially successful vaccines appear to induce protection that is relatively short-lived and it is likely that long-term protective immunity will be critical for making effective vaccines against our most challenging diseases such as AIDS and malaria.

Sequential inactivated (IPV) and live oral (OPV) poliovirus vaccines for preventing poliomyelitis

BACKGROUND

Poliomyelitis mainly affects unvaccinated children under five years of age, causing irreversible paralysis or even death. The oral polio vaccine (OPV) contains live attenuated virus, which can, in rare cases, cause a paralysis known as vaccine-associated paralytic polio (VAPP), and also vaccine-derived polioviruses (VDPVs) due to acquired neurovirulence after prolonged duration of replication. The incidence of poliomyelitis caused by wild polio virus (WPV) has declined dramatically since the introduction of OPV and later the inactivated polio vaccine (IPV), however, the cases of paralysis linked to the OPV are currently more frequent than those related to the WPV. Therefore, in 2016, the World Health Organization (WHO) recommended at least one IPV dose preceding routine immunisation with OPV to reduce VAPPs and VDPVs until polio could be eradicated.

OBJECTIVES

To assess the effectiveness, safety, and immunogenicity of sequential IPV-OPV immunisation schemes compared to either OPV or IPV alone.

SEARCH METHODS

In May 2019 we searched CENTRAL, MEDLINE, Embase, 14 other databases, three trials registers and reports of adverse effects on four web sites. We also searched the references of identified studies, relevant reviews and contacted authors to identify additional references.

SELECTION CRITERIA

Randomised controlled trials (RCTs), quasi-RCTs, controlled before-after studies, nationwide uncontrolled before-after studies (UBAs), interrupted time series (ITS) and controlled ITS comparing sequential IPV-OPV schedules (one or more IPV doses followed by one or more OPV doses) with IPV alone, OPV alone or non-sequential IPV-OPV combinations.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 21 studies: 16 RCTs involving 6407 healthy infants (age range 96 to 975 days, mean 382 days), one ITS with 28,330 infants and four nationwide studies (two ITS, two UBA). Ten RCTs were conducted in high-income countries; five in the USA, two in the UK, and one each in Chile, Israel, and Oman. The remaining six RCTs were conducted in middle-income countries; China, Bangladesh, Guatemala, India, and Thailand. We rated all included RCTs at low or unclear risk of bias for randomisation domains, most at high or unclear risk of attrition bias, and half at high or unclear risk for conflict of interests. Almost all RCTs were at low risk for the remaining domains. ITSs and UBAs were mainly considered at low risk of bias for most domains. IPV-OPV versus OPV It is uncertain if an IPV followed by OPV schedule is better than OPV alone at reducing the number of WPV cases (very low-certainty evidence); however, it may reduce VAPP cases by 54% to 100% (three nationwide studies; low-certainty evidence). There is little or no difference in vaccination coverage between IPV-OPV and OPV-only schedules (risk ratio (RR) 1.01, 95% confidence interval (CI) 0.96 to 1.06; 1 ITS study; low-certainty evidence). Similarly, there is little or no difference between the two schedule types for the number of serious adverse events (SAEs) (RR 0.88, 95% CI 0.46 to 1.70; 4 studies, 1948 participants; low-certainty evidence); or the number of people with protective humoral response P1 (moderate-certainty evidence), P2 (for the most studied schedule; two IPV doses followed by OPV; low-certainty evidence), and P3 (low-certainty evidence). Two IPV doses followed by bivalent OPV (IIbO) may reduce P2 neutralising antibodies compared to trivalent OPV (moderate-certainty evidence), but may make little or no difference to P1 or P2 neutralising antibodies following an IIO schedule or OPV alone (low-certainty evidence). Both IIO and IIbO schedules may increase P3 neutralising antibodies compared to OPV (moderate-certainty evidence). It may also lead to lower mucosal immunity given increased faecal excretion of P1 (low-certainty evidence), P2 and P3 (moderate-certainty evidence) after OPV challenge. IPV-OPV versus IPV It is uncertain if IPV-OPV is more effective than IPV alone at reducing the number of WPV cases (very low-certainty evidence). There were no data regarding VAPP cases. There is no clear evidence of a difference between IPV-OPV and OPV schedules for the number of people with protective humoral response (low- and moderate-certainty evidence). IPV-OPV schedules may increase mean titres of P1 neutralising antibodies compared to OPV alone (low- and moderate-certainty evidence), but the effect on P2 and P3 titres is not clear (very low- and moderate-certainty evidence). IPV-OPV probably reduces the number of people with P3 poliovirus faecal excretion after OPV challenge with IIO and IIOO sequences (moderate-certainty evidence), and may reduce the number with P2 (low-certainty evidence), but not with P1 (very low-certainty evidence). There may be little or no difference between the schedules in number of SAEs (RR 0.92, 95% CI 0.60 to 1.43; 2 studies, 1063 participants, low-certainty evidence). The number of persons with P2 protective humoral immunity and P2 neutralising antibodies are probably lower with most sequential schemes without P2 components (i.e. bOPV) than with trivalent OPV or IVP alone (moderate-certainty evidence). IPV (3)-OPV versus IPV (2)-OPV One study (137 participants) showed no clear evidence of a difference between three IPV doses followed by OPV and two IPV doses followed by OPV, on the number of people with P1 (RR 0.98, 95% CI 0.93 to 1.03), P2 (RR 1.00, 95% CI 0.97 to 1.03), or P3 (RR 1.01, 95% CI 0.97 to 1.05) protective humoral and intestinal immunity; all moderate-certainty evidence. This study did not report on any other outcomes.

AUTHORS' CONCLUSIONS

IPV-OPV compared to OPV may reduce VAPPs without affecting vaccination coverage, safety or humoral response, except P2 with sequential schemes without P2 components, but increase poliovirus faecal excretion after OPV challenge for some polio serotypes. Compared to IPV-only schedules, IPV-OPV may have little or no difference on SAEs, probably has little or no effect on persons with protective humoral response, may increase neutralising antibodies, and probably reduces faecal excretion after OPV challenge of certain polio serotypes. Using three IPV doses as part of a IPV-OPV schedule does not appear to be better than two IPV doses for protective humoral response. Sequential schedules during the transition from OPV to IPV-only immunisation schedules seems a reasonable option aligned with current WHO recommendations. Findings could help decision-makers to optimise polio vaccination policies, reducing inequities between countries.

Impact of Maternal Antibody on the Immunogenicity of Inactivated Polio Vaccine in Infants Immunized With Bivalent Oral Polio Vaccine: Implications for the Polio Eradication Endgame

Background

Quantifying interference of maternal antibodies with immune responses to varying dose schedules of inactivated polio vaccine (IPV) is important for the polio endgame as IPV replaces oral polio vaccine (OPV).

Methods

Type 2 poliovirus humoral and intestinal responses were analyzed using pre-IPV type 2 seropositivity as proxy for maternal antibodies from 2 trials in Latin America. Infants received 1 or 2 doses of IPV in sequential IPV-bivalent oral polio vaccine (bOPV) or mixed bOPV-IPV schedules.

Results

Among infants vaccinated with bOPV at age 6, 10, and 14 weeks of age and IPV at 14 weeks, those with type 2 pre-IPV seropositivity had lower seroprotection rates than seronegative infants at 4 weeks (92.7% vs 83.8%; difference, 8.9% [95% confidence interval, 0.6%-19.9%]; n = 260) and 22 weeks (82.7% vs 60.4%; difference, 22.3 [12.8%-32.4%]; n = 481) post-IPV. A second IPV at age 36 weeks resulted in 100% seroprotection in both groups. Among infants vaccinated with 1 IPV at age 8 weeks followed by 2 doses of bOPV, pre-IPV type 2-seropositive infants had lower seroprotection at age 28 weeks than those who were seronegative (93.0% vs 73.9%; difference, 19.6% [95% confidence interval, 7.3%-29.4%]; n = 168). A second dose of IPV at 16 weeks achieved >97% seroprotection at age 24 or 28 weeks, regardless of pre-IPV status. Poliovirus shedding after challenge with monovalent OPV, serotype 2, was higher in pre-IPV seropositive infants given sequential IPV-bOPV. No differences were observed in the mixed bOPV-IPV schedule.

Conclusions

The presence of maternal antibody is associated with lower type 2 post-IPV seroprotection rates among infants who receive a single dose of IPV. This impact persists until late in infancy and is overcome by a second IPV dose.

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.

Type 2 Poliovirus Detection after Global Withdrawal of Trivalent Oral Vaccine

BACKGROUND

Mass campaigns with oral poliovirus vaccine (OPV) have brought the world close to the eradication of wild poliovirus. However, to complete eradication, OPV must itself be withdrawn to prevent outbreaks of vaccine-derived poliovirus (VDPV). Synchronized global withdrawal of OPV began with serotype 2 OPV (OPV2) in April 2016, which presented the first test of the feasibility of eradicating all polioviruses.

METHODS

We analyzed global surveillance data on the detection of serotype 2 Sabin vaccine (Sabin-2) poliovirus and serotype 2 vaccine-derived poliovirus (VDPV2, defined as vaccine strains that are at least 0.6% divergent from Sabin-2 poliovirus in the viral protein 1 genomic region) in stool samples from 495,035 children with acute flaccid paralysis in 118 countries and in 8528 sewage samples from four countries at high risk for transmission; the samples were collected from January 1, 2013, through July 11, 2018. We used Bayesian spatiotemporal smoothing and logistic regression to identify and map risk factors for persistent detection of Sabin-2 poliovirus and VDPV2.

RESULTS

The prevalence of Sabin-2 poliovirus in stool samples declined from 3.9% (95% confidence interval [CI], 3.5 to 4.3) at the time of OPV2 withdrawal to 0.2% (95% CI, 0.1 to 2.7) at 2 months after withdrawal, and the detection rate in sewage samples declined from 71.0% (95% CI, 61.0 to 80.0) to 13.0% (95% CI, 8.0 to 20.0) during the same period. However, 12 months after OPV2 withdrawal, Sabin-2 poliovirus continued to be detected in stool samples (<0.1%; 95% CI, <0.1 to 0.1) and sewage samples (8.0%; 95% CI, 5.0 to 13.0) because of the use of OPV2 in response to VDPV2 outbreaks. Nine outbreaks were reported after OPV2 withdrawal and were associated with low coverage of routine immunization (odds ratio, 1.64 [95% CI, 1.14 to 2.54] per 10% absolute decrease) and low levels of population immunity (odds ratio, 2.60 [95% CI, 1.35 to 5.59] per 10% absolute decrease) within affected countries.

CONCLUSIONS

High population immunity has facilitated the decline in the prevalence of Sabin-2 poliovirus after OPV2 withdrawal and restricted the circulation of VDPV2 to areas known to be at high risk for transmission. The prevention of VDPV2 outbreaks in these known areas before the accumulation of substantial cohorts of children susceptible to type 2 poliovirus remains a high priority. (Funded by the Bill and Melinda Gates Foundation and the World Health Organization.).

Polio endgame risks and the possibility of restarting the use of oral poliovirus vaccine

INTRODUCTION

Ending all cases of poliomyelitis requires successful cessation of all oral poliovirus vaccine (OPV), but the Global Polio Eradication Initiative (GPEI) partners should consider the possibility of an OPV restart.

AREAS COVERED

We review the risks of continued live poliovirus transmission after OPV cessation and characterize events that led to OPV restart in a global model that focused on identifying optimal strategies for OPV cessation and the polio endgame. Numerous different types of events that occurred since the globally coordinated cessation of serotype 2-containing OPV in 2016 highlight the possibility of continued outbreaks after homotypic OPV cessation. Modeling suggests a high risk of uncontrolled outbreaks once more than around 5,000 homotypic polio cases occur after cessation of an OPV serotype, at which point restarting OPV would become necessary to protect most populations. Current efforts to sunset the GPEI and transition its responsibilities to national governments poses risks that may limit the ability to implement management strategies needed to minimize the probability of an OPV restart.

EXPERT COMMENTARY

OPV restart remains a real possibility, but risk management choices made by the GPEI partners and national governments can reduce the risks of this low-probability but high-consequence event.

Breaking the Last Chains of Poliovirus Transmission: Progress and Challenges in Global Polio Eradication

Since the launch of the Global Polio Eradication Initiative (GPEI), paralytic cases associated with wild poliovirus (WPV) have fallen from ∼350,000 in 1988 to 22 in 2017. WPV type 2 (WPV2) was last detected in 1999, WPV3 in 2012, and WPV1 appeared to be localized to Pakistan and Afghanistan in 2017. Through continuous refinement, the GPEI has overcome operational and biological challenges far more complex and daunting than originally envisioned. Operational challenges had led to sustained WPV endemicity in core reservoirs and widespread dissemination to polio-free countries. The biological challenges derive from intrinsic limitations to the oral poliovirus vaccine: ( a) reduced immunogenicity in high-risk settings and ( b) genetic instability, leading to repeated outbreaks of circulating vaccine-derived polioviruses and prolonged infections in individuals with primary immunodeficiencies. As polio eradication enters its multifaceted endgame, the GPEI, with its technical, operational, and social innovations, stands as the preeminent model for control of vaccine-preventable diseases worldwide.

Immunogenicity of sequential inactivated and oral poliovirus vaccines (OPV) versus inactivated poliovirus vaccine (IPV) alone in healthy infants: A systematic review and meta-analysis

BACKGROUND

The emergence of vaccine-associated paralytic poliomyelitis has become an ongoing burden of poliomyelitis. During this special period from OPV to IPV-only immunization schedule, we did a meta-analysis to compare the immunogenicity of sequential IPV and OPV versus IPV alone in healthy infants.

METHODS

This systematic review and meta-analysis was registered at international prospective register of systematic reviews (PROSPERO), and the number was CRD42017054889. We performed it as described.

RESULTS

Finally, 6 articles were qualified for our review. The results showed that seroconversion rates against all 3 serotype polioviruses were non-inferior and Geometric mean antibody titers (GMTs) were superior in sequential schedules compared with IPV-only schedule. Thus, the sequential vaccination schedules could induce a stronger immunogenicity.

CONCLUSIONS

To decrease vaccine-associated and vaccine-derived poliomyelitis, it is a reasonable option to select sequential schedules during this special transition from OPV to IPV-only immunization schedule, which coincides with the current WHO recommendations.

Seroprevalence of antibodies against the three serotypes of poliovirus and IPV vaccine response in adult solid organ transplant candidates

OBJECTIVES

To assess the prevalence of protective antibody titers to polioviruses in adults candidates for solid organ transplant (SOT), and to assess the immunogenic response to inactivated polio vaccine in this population.

METHODS

The study included SOT candidates referred to Immunization Reference Centre of Evandro Chagas National Institute of Infectious Diseases from March 2013 to January 2016. It was conducted in 2 phases. The first one, a cross-sectional seroprevalence study, followed by an uncontrolled analysis of vaccine response among patients without protective antibody titers at baseline. Antibody titers to poliomyelitis were determined by microneutralization assay.

RESULTS

Among 206 SOT candidates included, 156 (76%) had protective antibody titers to all poliovirus serotypes (95% CI: 70-81%). Proven history of oral vaccination in childhood was not associated with higher seroprevalence of protective antibody. In 97% of individuals without protective antibody titers at baseline, there was adequate vaccine response with one dose of inactivated polio vaccine.

CONCLUSIONS

A relevant proportion of adult candidates for SOT does not have protective titers of antibodies to one or more poliovirus serotype. One dose of inactivated vaccine elicited protective antibody titers in 97% of these subjects and should be routinely prescribed prior to SOT.

Assessing the stability of polio eradication after the withdrawal of oral polio vaccine

The oral polio vaccine (OPV) contains live-attenuated polioviruses that induce immunity by causing low virulence infections in vaccine recipients and their close contacts. Widespread immunization with OPV has reduced the annual global burden of paralytic poliomyelitis by a factor of 10,000 or more and has driven wild poliovirus (WPV) to the brink of eradication. However, in instances that have so far been rare, OPV can paralyze vaccine recipients and generate vaccine-derived polio outbreaks. To complete polio eradication, OPV use should eventually cease, but doing so will leave a growing population fully susceptible to infection. If poliovirus is reintroduced after OPV cessation, under what conditions will OPV vaccination be required to interrupt transmission? Can conditions exist in which OPV and WPV reintroduction present similar risks of transmission? To answer these questions, we built a multi-scale mathematical model of infection and transmission calibrated to data from clinical trials and field epidemiology studies. At the within-host level, the model describes the effects of vaccination and waning immunity on shedding and oral susceptibility to infection. At the between-host level, the model emulates the interaction of shedding and oral susceptibility with sanitation and person-to-person contact patterns to determine the transmission rate in communities. Our results show that inactivated polio vaccine (IPV) is sufficient to prevent outbreaks in low transmission rate settings and that OPV can be reintroduced and withdrawn as needed in moderate transmission rate settings. However, in high transmission rate settings, the conditions that support vaccine-derived outbreaks have only been rare because population immunity has been high. Absent population immunity, the Sabin strains from OPV will be nearly as capable of causing outbreaks as WPV. If post-cessation outbreak responses are followed by new vaccine-derived outbreaks, strategies to restore population immunity will be required to ensure the stability of polio eradication.

Oral polio vaccine (OPV) has played an essential role in the elimination of wild poliovirus (WPV). OPV contains attenuated (weakened) yet transmissible viruses that can spread from person to person. In its attenuated form, this spread is beneficial as it generates population immunity. However, the attenuation of OPV is unstable and it can, in rare instances, revert to a virulent form and cause vaccine-derived outbreaks of paralytic poliomyelitis. Thus, OPV is both a vaccine and a source of poliovirus, and for complete eradication, its use in vaccination must be ended. After OPV is no longer used in routine immunization, as with the cessation of type 2 OPV in 2016, population immunity to polioviruses will decline. A key question is how this loss of population immunity will affect the potential of OPV viruses to spread within and across communities. To address this, we examined the roles of immunity, sanitation, and social contact in limiting OPV transmission. Our results derive from an extensive review and synthesis of vaccine trial data and community epidemiological studies. Shedding, oral susceptibility to infection, and transmission data are analyzed to systematically explain and model observations of WPV and OPV circulation. We show that in high transmission rate settings, falling population immunity after OPV cessation will lead to conditions in which OPV and WPV are similarly capable of causing outbreaks, and that this conclusion is compatible with the known safety of OPV prior to global cessation. Novel strategies will be required to ensure the stability of polio eradication for all time.

Seronegativity to polio viruses among previously immunized adult candidates to solid organ transplantation

In the current effort to eliminate polio from the world, it is important to recognize and vaccinate susceptible groups, especially immunocompromised patients living in countries where attenuated polio vaccine is still used. In this report, we describe the frequency of protective antibodies in a small sample of adult SOT candidates in whom previous vaccination could be ascertained. Patients included in this report were selected among the participants of an ongoing prospective study carried out at the Reference Center for Special Immunobiologicals of the Evandro Chagas National Institute of Infectious Diseases in Rio de Janeiro, Brazil. Among the first 100 patients enrolled in this study, only seven adult SOT candidates had proven polio vaccination at childhood. Three of these seven patients (43%) had no protective antibody titers to one or more poliovirus subtype before solid organ transplant. Proven childhood vaccination against polio does not reliably provide lifelong protective antibody titers for adult SOT candidates and should not be used as a criterion to analyze the need for vaccination in this population.

Current state and challenges in developing oral vaccines

While vaccination remains the most cost effective strategy for disease prevention, communicable diseases persist as the second leading cause of death worldwide. There is a need to design safe, novel vaccine delivery methods to protect against unaddressed and emerging diseases. Development of vaccines administered orally is preferable to traditional injection-based formulations for numerous reasons including improved safety and compliance, and easier manufacturing and administration. Additionally, the oral route enables stimulation of humoral and cellular immune responses at both systemic and mucosal sites to establish broader and long-lasting protection. However, oral delivery is challenging, requiring formulations to overcome the harsh gastrointestinal (GI) environment and avoid tolerance induction to achieve effective protection. Here we address the rationale for oral vaccines, including key biological and physicochemical considerations for next-generation oral vaccine design.

The polio endgame: rationale behind the change in immunisation

The decades long effort to eradicate polio is nearing the final stages and oral polio vaccine (OPV) is much to thank for this success. As cases of wild poliovirus continue to dwindle, cases of paralysis associated with OPV itself have become a concern. As type-2 poliovirus (one of three) has been certified eradicated and a large proportion of OPV-related paralysis is caused by the type-2 component of OPV, the World Health Assembly endorsed the phased withdrawal of OPV and the introduction of inactivated polio vaccine (IPV) into routine immunisation schedules as a crucial step in the polio endgame plan. The rapid pace of IPV scale-up and uptake required adequate supply, planning, advocacy, training and operational readiness. Similarly, the synchronised switch from trivalent OPV (all three types) to bivalent OPV (types 1 and 3) involved an unprecedented level of global coordination and country commitment. The important shift in vaccination policy seen through global IPV introduction and OPV withdrawal represents an historical milestone reached in the polio eradication effort.

Long-term evaluation of mucosal and systemic immunity and protection conferred by different polio booster vaccines

Oral polio vaccine (OPV) and Inactivated Polio Vaccine (IPV) have distinct advantages and limitations. IPV does not provide mucosal immunity and introduction of IPV to mitigate consequences of circulating vaccine-derived polio virus from OPV has very limited effect on transmission and OPV campaigns are essential for interrupting wild polio virus transmission, even in developed countries with a high coverage of IPV and protected sewer systems. The problem is magnified in many countries with limited resources. Requirement of refrigeration for storage and transportation for both IPV and OPV is also a major challenge in developing countries. Therefore, we present here long-term studies on comparison of a plant-based booster vaccine, which is free of virus and cold chain with IPV boosters and provide data on mucosal and systemic immunity and protection conferred by neutralizing antibodies.

Mice were primed subcutaneously with IPV and boosted orally with lyophilized plant cells containing 1 μg or 25 μg polio viral protein 1 (VP1), once a month for three months or a single booster one year after the first prime. Our results show that VP1-IgG1 titers in single or double dose IPV dropped to background levels after one year of immunization. This decrease correlated with >50% reduction in seropositivity in double dose and <10% seropositivity in single dose IPV against serotype 1. Single dose IPV offered no or minimal protection against serotype 1 and 2 but conferred protection against serotype 3. VP1-IgA titers were negligible in IPV single or double dose vaccinated mice. VP1 antigen with two plant-derived adjuvants induced significantly high level and long lasting VP1-IgG1, IgA and neutralizing antibody titers (average 4.3–6.8 log2 titers). Plant boosters with VP1 and plant derived adjuvants maintained the same level titers from 29 to 400 days and conferred the same level of protection against all three serotypes throughout the duration of this study. Even during period, when no plant booster was given (∼260 days), VP1-IgG1 titers were maintained at high levels. Lyophilized plant cells expressing VP1 can be stored without losing efficacy, eliminating cold chain. Virus-free, cold-chain free vaccine is ready for further clinical development.

Costs and Benefits of Including Inactivated in Addition to Oral Poliovirus Vaccine in Outbreak Response After Cessation of Oral Poliovirus Vaccine Use

Background: After stopping serotype 2-containing oral poliovirus vaccine use, serotype 2 poliovirus outbreaks may still occur and require outbreak response supplemental immunization activities (oSIAs). Current oSIA plans include the use of both serotype 2 monovalent oral poliovirus vaccine (mOPV2) and inactivated poliovirus vaccine (IPV). Methods: We used an existing model to compare the effectiveness of mOPV2 oSIAs with or without IPV in response to a hypothetical postcessation serotype 2 outbreak in northwest Nigeria. We considered strategies that co-administer IPV with mOPV2, use IPV only for older age groups, or use only IPV during at least one oSIA. We considered the cost and supply implications and estimated from a societal perspective the incremental cost-effectiveness and incremental net benefits of adding IPV to oSIAs in the context of this hypothetical outbreak in 2017. Results: Adding IPV to the first or second oSIA resulted in a 4% to 6% reduction in expected polio cases compared to exclusive mOPV2 oSIAs. We found the greatest benefit of IPV use if added preemptively as a ring around the initial oSIA target population, and negligible benefit if added to later oSIAs or older age groups. We saw an increase in expected polio cases if IPV replaced mOPV2 during an oSIA. None of the oSIA strategies that included IPV for this outbreak represented a cost-effective or net beneficial intervention compared to reliance on mOPV2 only. Conclusions: While adding IPV to oSIAs results in marginal improvements in performance, the poor cost-effectiveness and current limited IPV supply make it economically unattractive for high-risk settings in which IPV does not significantly affect transmission.

The potential benefits of a new poliovirus vaccine for long-term poliovirus risk management

Aim: To estimate the incremental net benefits (INBs) of a hypothetical ideal vaccine with all of the advantages and no disadvantages of existing oral and inactivated poliovirus vaccines compared with current vaccines available for future outbreak response. Methods: INB estimates based on expected costs and polio cases from an existing global model of long-term poliovirus risk management. Results: Excluding the development costs, an ideal poliovirus vaccine could offer expected INBs of US$1.6 billion. The ideal vaccine yields small benefits in most realizations of long-term risks, but great benefits in low-probability–high-consequence realizations. Conclusion: New poliovirus vaccines may offer valuable insurance against long-term poliovirus risks and new vaccine development efforts should continue as the world gathers more evidence about polio endgame risks.

Plant-based oral vaccines against zoonotic and non-zoonotic diseases

The shared diseases between animals and humans are known as zoonotic diseases and spread infectious diseases among humans. Zoonotic diseases are not only a major burden to livestock industry but also threaten humans accounting for >60% cases of human illness. About 75% of emerging infectious diseases in humans have been reported to originate from zoonotic pathogens. Because antibiotics are frequently used to protect livestock from bacterial diseases, the development of antibiotic-resistant strains of epidemic and zoonotic pathogens is now a major concern. Live attenuated and killed vaccines are the only option to control these infectious diseases and this approach has been used since 1890. However, major problems with this approach include high cost and injectable vaccines is impractical for >20 billion poultry animals or fish in aquaculture. Plants offer an attractive and affordable platform for vaccines against animal diseases because of their low cost, and they are free of attenuated pathogens and cold chain requirement. Therefore, several plant-based vaccines against human and animals diseases have been developed recently that undergo clinical and regulatory approval. Plant-based vaccines serve as ideal booster vaccines that could eliminate multiple boosters of attenuated bacteria or viruses, but requirement of injectable priming with adjuvant is a current limitation. So, new approaches like oral vaccines are needed to overcome this challenge. In this review, we discuss the progress made in plant-based vaccines against zoonotic or other animal diseases and future challenges in advancing this field.

Cold chain and virus-free chloroplast-made booster vaccine to confer immunity against different poliovirus serotypes

The WHO recommends complete withdrawal of oral polio vaccine (OPV) type 2 by April 2016 globally and replacing with at least one dose of inactivated poliovirus vaccine (IPV). However, high-cost, limited supply of IPV, persistent circulating vaccine-derived polioviruses transmission and need for subsequent boosters remain unresolved. To meet this critical need, a novel strategy of a low-cost cold chain-free plant-made viral protein 1 (VP1) subunit oral booster vaccine after single IPV dose is reported. Codon optimization of the VP1 gene enhanced expression by 50-fold in chloroplasts. Oral boosting of VP1 expressed in plant cells with plant-derived adjuvants after single priming with IPV significantly increased VP1-IgG1 and VP1-IgA titres when compared to lower IgG1 or negligible IgA titres with IPV injections. IgA plays a pivotal role in polio eradication because of its transmission through contaminated water or sewer systems. Neutralizing antibody titres (~3.17-10.17 log2 titre) and seropositivity (70-90%) against all three poliovirus Sabin serotypes were observed with two doses of IPV and plant-cell oral boosters but single dose of IPV resulted in poor neutralization. Lyophilized plant cells expressing VP1 stored at ambient temperature maintained efficacy and preserved antigen folding/assembly indefinitely, thereby eliminating cold chain currently required for all vaccines. Replacement of OPV with this booster vaccine and the next steps in clinical translation of FDA-approved antigens and adjuvants are discussed.

Population Immunity against Serotype-2 Poliomyelitis Leading up to the Global Withdrawal of the Oral Poliovirus Vaccine: Spatio-temporal Modelling of Surveillance Data

BACKGROUND

Global withdrawal of serotype-2 oral poliovirus vaccine (OPV2) took place in April 2016. This marked a milestone in global polio eradication and was a public health intervention of unprecedented scale, affecting 155 countries. Achieving high levels of serotype-2 population immunity before OPV2 withdrawal was critical to avoid subsequent outbreaks of serotype-2 vaccine-derived polioviruses (VDPV2s).

METHODS AND FINDINGS

In August 2015, we estimated vaccine-induced population immunity against serotype-2 poliomyelitis for 1 January 2004-30 June 2015 and produced forecasts for April 2016 by district in Nigeria and Pakistan. Population immunity was estimated from the vaccination histories of children <36 mo old identified with non-polio acute flaccid paralysis (AFP) reported through polio surveillance, information on immunisation activities with different oral poliovirus vaccine (OPV) formulations, and serotype-specific estimates of the efficacy of these OPVs against poliomyelitis. District immunity estimates were spatio-temporally smoothed using a Bayesian hierarchical framework. Coverage estimates for immunisation activities were also obtained, allowing for heterogeneity within and among districts. Forward projections of immunity, based on these estimates and planned immunisation activities, were produced through to April 2016 using a cohort model. Estimated population immunity was negatively correlated with the probability of VDPV2 poliomyelitis being reported in a district. In Nigeria and Pakistan, declines in immunity during 2008-2009 and 2012-2013, respectively, were associated with outbreaks of VDPV2. Immunity has since improved in both countries as a result of increased use of trivalent OPV, and projections generally indicated sustained or improved immunity in April 2016, such that the majority of districts (99% [95% uncertainty interval 97%-100%] in Nigeria and 84% [95% uncertainty interval 77%-91%] in Pakistan) had >70% population immunity among children <36 mo old. Districts with lower immunity were clustered in northeastern Nigeria and northwestern Pakistan. The accuracy of immunity estimates was limited by the small numbers of non-polio AFP cases in some districts, which was reflected by large uncertainty intervals. Forecasted improvements in immunity for April 2016 were robust to the uncertainty in estimates of baseline immunity (January-June 2015), vaccine coverage, and vaccine efficacy.

CONCLUSIONS

Immunity against serotype-2 poliomyelitis was forecasted to improve in April 2016 compared to the first half of 2015 in Nigeria and Pakistan. These analyses informed the endorsement of OPV2 withdrawal in April 2016 by the WHO Strategic Advisory Group of Experts on Immunization.

Immunogenicity of Two Different Sequential Schedules of Inactivated Polio Vaccine Followed by Oral Polio Vaccine Versus Oral Polio Vaccine Alone in Healthy Infants in China

BACKGROUND

Two vaccination schedules where inactivated polio vaccine (IPV) was followed by oral polio vaccine (OPV) were compared to an OPV-only schedule.

METHODS

Healthy Chinese infants received a 3-dose primary series of IPV-OPV-OPV (Group A), IPV-IPV-OPV (Group B), or OPV-OPV-OPV (Group C) at 2, 3, and 4 months of age. At pre-Dose 1, 1-month, and 14-months post-Dose 3, polio 1, 2, and 3 antibody titers were assessed by virus-neutralizing antibody assay with Sabin or wild-type strains. Adverse events were monitored.

RESULTS

Anti-polio 1, 2, and 3 titers were ≥8 (1/dil) in >99% of participants, and Group A and Group B were noninferior to Group C at 1-month post-Dose 3 as assessed by Sabin strain-based assay (SSBA). In Group A 1-month post-Dose 3, there was no geometric mean antibody titers (GMT) differences for types 1 and 3; type 2 GMTs were ≈3-fold higher by wild-type strain-based assay (WTBA) versus SSBA. For Group B, GMTs were ≈1.7- and 3.6-fold higher for types 1 and 2 via WTBA, while type 3 GMTs were similar. For Group C, GMTs were ≈6.3- and 2-fold higher for types 1 and 3 with SSBA, and type 2 GMTs were similar. Antibodies persisted in >96.6% of participants. Adverse event incidence in each group was similar.

CONCLUSIONS

A primary series of 1 or 2 IPV doses followed by 2 or 1 OPV doses was immunogenic and noninferior to an OPV-only arm. SSBA was better at detecting antibodies elicited by OPV with antibody titers correlated to the number of OPV doses (NCT01475539).

Coverage estimates and patterns of inactivated poliovirus vaccine (IPV) use prior to and during the polio eradication endgame, Jinan City, China, 2010-2015

BACKGROUND

Use of inactivated poliovirus vaccine (IPV) in Jinan during the polio eradication endgame has not been previously documented. Two IPV-containing vaccines were made available as an option for Jinan parents in 2009. We describe coverage levels and patterns of use of IPV over time using data from the Jinan Childhood Immunization Information Management System (JNCIIMS).

METHODS

Children born between January 2010 and December 2014 who were registered in JNCIIMS were included in this study. Vaccination records were obtained from JNCIIMS on April 30, 2015. JNCIIMS distinguishes among available poliovirus vaccines; doses administered data were used to describe IPV usage over time. We identified the polio vaccination sequences used by children in the 2012 and 2013 birth cohorts. Coverage estimates were analyzed by birth cohort and migration status. We developed 3 categories for analysis: "resident child," "migrant child" and "other child" according to migration status.

RESULTS

In total, 12,354 (11.7%) IPV, 5,893(5.6%) DTP-IPV-Hib vaccine and 87,054(82.7%) OPV doses were administered to children in the 2010 to 2014 birth cohorts. The proportion of children using an IPV-only schedule increased each year, consistent with the introduction of IPV that is called for by the Polio Eradication Endgame Strategic Plan 2013-2018. During this time, 4.7% children used a schedule containing both IPV and oral poliovirus vaccine (OPV). In the 2012 to 2013 birth cohorts, 14.4% children used an IPV-only schedule; 5.7% children used a sequential schedule, and 79.9% used OPV-only schedule. Use of IPV only schedules was higher among migrant children than among resident children. Among those sequential schedule using both IPV and OPV, 87.2% children used IPV for the first dose and 12.8% used OPV for the first dose.

CONCLUSIONS

JNCIIMS provided a mechanism for tracking IPV and OPV vaccination patterns, and showed areas in need of improvement. Ensuring appropriately sequenced IPV and OPV supports reduction of risk of vaccine associated paralytic polio.

Preventing Vaccine-Derived Poliovirus Emergence during the Polio Endgame

Reversion and spread of vaccine-derived poliovirus (VDPV) to cause outbreaks of poliomyelitis is a rare outcome resulting from immunisation with the live-attenuated oral poliovirus vaccines (OPVs). Global withdrawal of all three OPV serotypes is therefore a key objective of the polio endgame strategic plan, starting with serotype 2 (OPV2) in April 2016. Supplementary immunisation activities (SIAs) with trivalent OPV (tOPV) in advance of this date could mitigate the risks of OPV2 withdrawal by increasing serotype-2 immunity, but may also create new serotype-2 VDPV (VDPV2). Here, we examine the risk factors for VDPV2 emergence and implications for the strategy of tOPV SIAs prior to OPV2 withdrawal. We first developed mathematical models of VDPV2 emergence and spread. We found that in settings with low routine immunisation coverage, the implementation of a single SIA increases the risk of VDPV2 emergence. If routine coverage is 20%, at least 3 SIAs are needed to bring that risk close to zero, and if SIA coverage is low or there are persistently "missed" groups, the risk remains high despite the implementation of multiple SIAs. We then analysed data from Nigeria on the 29 VDPV2 emergences that occurred during 2004-2014. Districts reporting the first case of poliomyelitis associated with a VDPV2 emergence were compared to districts with no VDPV2 emergence in the same 6-month period using conditional logistic regression. In agreement with the model results, the odds of VDPV2 emergence decreased with higher routine immunisation coverage (odds ratio 0.67 for a 10% absolute increase in coverage [95% confidence interval 0.55-0.82]). We also found that the probability of a VDPV2 emergence resulting in poliomyelitis in >1 child was significantly higher in districts with low serotype-2 population immunity. Our results support a strategy of focused tOPV SIAs before OPV2 withdrawal in areas at risk of VDPV2 emergence and in sufficient number to raise population immunity above the threshold permitting VDPV2 circulation. A failure to implement this risk-based approach could mean these SIAs actually increase the risk of VDPV2 emergence and spread.

Immunogenicity of a new routine vaccination schedule for global poliomyelitis prevention: an open-label, randomised controlled trial

BACKGROUND

Polio eradication needs a new routine immunisation schedule--three or four doses of bivalent type 1 and type 3 oral poliovirus vaccine (bOPV) and one dose of inactivated poliovirus vaccine (IPV), but no immunogenicity data are available for this schedule. We aimed to assess immunogenicity of this vaccine schedule.

METHODS

We did an open-label, randomised controlled trial in four centres in India. After informed consent was obtained from a parent or legally acceptable representative, healthy newborn babies were randomly allocated to one of five groups: trivalent OPV (tOPV); tOPV plus IPV; bOPV; bOPV plus IPV; or bOPV plus two doses of IPV (2IPV). The key eligibility criteria were: full-term birth (≥37 weeks of gestation); birthweight ≥2·5 kg; and Apgar score of 9 or more. OPV was administered at birth, 6 weeks, 10 weeks, and 14 weeks; IPV was administered intramuscularly at 14 weeks. The primary study objective was to investigate immunogenicity of the new vaccine schedule, assessed by seroconversion against poliovirus types 1, 2, and 3 between birth and 18 weeks in the per-protocol population (all participants with valid serology results on cord blood and at 18 weeks). Neutralisation assays tested cord blood and sera collected at 14 weeks, 18 weeks, 19 weeks, and 22 weeks by investigators masked to group allocation. This trial was registered with the India Clinical Trials Registry, number CTRI/2013/06/003722.

FINDINGS

Of 900 newborn babies enrolled between June 13 and Aug 29, 2013, 782 (87%) completed the per-protocol requirements. Between birth and age 18 weeks, seroconversion against poliovirus type 1 in the tOPV group occurred in 162 of 163 (99·4%, 95% CI 96·6-100), in 150 (98·0%, 94·4-99·6) of 153 in the tOPV plus IPV group, in 153 (98·7%, 95·4-99·8) of 155 in the bOPV group, in 155 (99·4%, 96·5-100) of 156 in the bOPV plus IPV group, and in 154 (99·4%, 96·5-100) of 155 in the bOPV plus 2IPV group. Seroconversion against poliovirus type 2 occurred in 157 (96·3%, 92·2-98·6) of 163 in the tOPV group, 153 (100%, 97·6-100·0) of 153 in the tOPV plus IPV group, 29 (18·7%, 12·9-25·7) of 155 in the bOPV group, 107 (68·6%, 60·7-75·8) of 156 in the bOPV plus IPV group, and in 121 (78·1%, 70·7-84·3) of 155 in the bOPV plus 2IPV group. Seroconversion against poliovirus type 3 was achieved in 147 (90·2%, 84·5-94·3) of 163 in the tOPV group, 152 (99·3%, 96·4-100) of 153 in the tOPV plus IPV group, 151 (97·4%, 93·5-99·3) of 155 in the bOPV group, 155 (99·4%, 96·5-100) of 156 in the bOPV plus IPV group, and 153 (98·7%, 95·4-99·8) of 155 in the bOPV plus 2IPV group. Superiority was achieved for vaccine regimens including IPV against poliovirus type 3 compared with those not including IPV (tOPV plus IPV vs tOPV alone, p=0·0008; and bOPV plus IPV vs bOPV alone, p=0·0153). 12 serious adverse events occurred (six in the tOPV group, one in the tOPV plus IPV group, three in the bOPV group, zero in the bOPV plus IPV group, and two in the bOPV plus 2IPV group), none of which was attributed to the trial intervention.

INTERPRETATION

The new vaccination schedule improves immunogenicity against polioviruses, especially against poliovirus type 3.

FUNDING

WHO, through a grant from Rotary International (grant number 59735).

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.