Genetic stabilization of attenuated oral vaccines against poliovirus types 1 and 3

Pharmacovigilance in Vaccines: Importance, Main Aspects, Perspectives, and Challenges-A Narrative Review

Pharmacovigilance plays a central role in safeguarding public health by continuously monitoring the safety of vaccines, being critical in a climate of vaccine hesitancy, where public trust is paramount. Pharmacovigilance strategies employed to gather information on adverse events following immunization (AEFIs) include pre-registration data, media reports, clinical trials, and societal reporting. Early detection of AEFIs during clinical trials is crucial for thorough safety analysis and preventing serious reactions once vaccines are deployed. This review highlights the importance of societal reporting, encompassing contributions from community members, healthcare workers, and pharmaceutical companies. Technological advancements such as quick response (QR) codes can facilitate prompt AEFI reporting. While vaccines are demonstrably safe, the possibility of adverse events necessitates continuous post-marketing surveillance. However, underreporting remains a challenge, underscoring the critical role of public engagement in pharmacovigilance. This narrative review comprehensively examines and synthesizes key aspects of virus vaccine pharmacovigilance, with special considerations for specific population groups. We explore applicable legislation, the spectrum of AEFIs associated with major vaccines, and the unique challenges and perspectives surrounding pharmacovigilance in this domain.

Application of MPBT Assay for Multiplex Determination of Infectious Titers and for Selection of the Optimal Formulation for the Trivalent Novel Oral Poliovirus Vaccine

Recently, a multiplex PCR-based titration (MPBT) assay was developed for simultaneous determination of infectious titers of all three Sabin strains of the oral poliovirus vaccine (OPV) to replace the conventional CCID50 assay, which is both time-consuming and laborious. The MPBT assay was shown to be reproducible, robust and sensitive. The conventional and MPBT assays showed similar results and sensitivity. The MPBT assay can be completed in two to three days, instead of ten days for the conventional assay. To prevent attenuated vaccine strains of poliovirus from reversion to virulence, a novel, genetically stable OPV (nOPV) was developed by modifying the genomes of conventional Sabin strains used in OPV. In this work, we evaluated the MPBT assay as a rapid screening tool to support trivalent nOPV (tnOPV) formulation development by simultaneous titration of the three nOPV strains to confirm stability as needed, for the selection of the lead tnOPV formulation candidate. We first assessed the ability of the MPBT assay to discriminate a 0.5 log10 titer difference by titrating the two tnOPV samples (undiluted and threefold-diluted) on the same plate. Once the assay was shown to be discriminating, we then tested different formulations of tnOPV drug products (DPs) that were subjected to different exposure times at 37 °C (untreated group and treated groups: 2 and 7 days at 37 °C), and to three freeze and thaw (FT) cycles. Final confirmation of the down selected formulation candidates was achieved by performing the conventional CCID50 assay, comparing the stability of untreated and treated groups and FT stability testing on the top three candidates. The results showed that the MPBT assay generates similar titers as the conventional assay. By testing two trivalent samples in the same plate, the assay can differentiate a 0.5 log10 difference between the titers of the tested nOPV samples. Also, the assay was able to detect the gradual degradation of nOPV viruses with different formulation compositions and under different time/temperature conditions and freeze/thaw cycles. We found that there were three tnOPV formulations which met the stability criteria of less than 0.5 log10 loss after 2 days' exposure to 37 ℃ and after three FT cycles, maintaining the potency of all three serotypes in these formulations. The ability of the MPBT assay to titrate two tnOPV lots (six viruses) in the same plate makes it cheaper and gives it a higher throughput for rapid screening. The assay detected the gradual degradation of the tnOPV and was successful in the selection of optimal formulations for the tnOPV. The results demonstrated that the MPBT method can be used as a stability indicating assay to assess the thermal stability of the nOPV. It can be used for rapid virus titer determination during the vaccine manufacturing process, and in clinical trials. The MPBT assay can be automated and applied for other viruses, including those with no cytopathic effect.

An efficient trans complementation system for in vivo replication of defective poliovirus mutants

The picornavirus genome encodes a large, single polyprotein that is processed by viral proteases to form an active replication complex. The replication complex is formed with the viral genome, host proteins, and viral proteins that are produced/translated directly from each of the viral genomes (viral proteins provided in cis). Efficient complementation in vivo of replication complex formation by viral proteins provided in trans, thus exogenous or ectopically expressed viral proteins, remains to be demonstrated. Here, we report an efficient trans complementation system for the replication of defective poliovirus (PV) mutants by a viral polyprotein precursor in HEK293 cells. Viral 3AB in the polyprotein, but not 2BC, was processed exclusively in cis. Replication of a defective PV replicon mutant, with a disrupted cleavage site for viral 3Cpro protease between 3Cpro and 3Dpol (3C/D[A/G] mutant) could be rescued by a viral polyprotein provided in trans. Only a defect of 3Dpol activity of the replicon could be rescued in trans; inactivating mutations in 2CATPase/hel, 3B, and 3Cpro of the replicon completely abrogated the trans-rescued replication. An intact N-terminus of the 3Cpro domain of the 3CDpro provided in trans was essential for the trans-active function. By using this trans complementation system, a high-titer defective PV pseudovirus (PVpv) (>107 infectious units per mL) could be produced with the defective mutants, whose replication was completely dependent on trans complementation. This work reveals potential roles of exogenous viral proteins in PV replication and offers insights into protein/protein interaction during picornavirus infection.

IMPORTANCE

Viral polyprotein processing is an elaborately controlled step by viral proteases encoded in the polyprotein; fully processed proteins and processing intermediates need to be correctly produced for replication, which can be detrimentally affected even by a small modification of the polyprotein. Purified/isolated viral proteins can retain their enzymatic activities required for viral replication, such as protease, helicase, polymerase, etc. However, when these proteins of picornavirus are exogenously provided (provided in trans) to the viral replication complex with a defective viral genome, replication is generally not rescued/complemented, suggesting the importance of viral proteins endogenously provided (provided in cis) to the replication complex. In this study, I discovered that only the viral polymerase activity of poliovirus (PV) (the typical member of picornavirus family) could be efficiently rescued by exogenously expressed viral proteins. The current study reveals potential roles for exogenous viral proteins in viral replication and offers insights into interactions during picornavirus infection.

The Milk of Cows Immunized with Trivalent Inactivated Vaccines Provides Broad-Spectrum Passive Protection against Hand, Foot, and Mouth Disease in Neonatal Mice

Hand, foot, and mouth disease (HFMD) is a contagious viral infection predominantly affecting infants and young children, caused by multiple enteroviruses, including Enterovirus 71 (EV71), Coxsackievirus A16 (CA16), Coxsackievirus A10 (CA10), and Coxsackievirus A6 (CA6). The high pathogenicity of HFMD has garnered significant attention. Currently, there is no specific treatment or broad-spectrum preventive measure available for HFMD, and existing monovalent vaccines have limited impact on the overall incidence or prevalence of the disease. Consequently, with the emergence of new viral strains driven by vaccine pressure, there is an urgent need to develop strategies for the rapid response and control of new outbreaks. In this study, we demonstrated the broad protective effect of maternal antibodies against three types of HFMD by immunizing mother mice with a trivalent inactivated vaccine targeting EV71, CA16, and CA10, using a neonatal mouse challenge model. Based on the feasibility of maternal antibodies as a form of passive immunization to prevent HFMD, we prepared a multivalent antiviral milk by immunizing dairy cows with the trivalent inactivated vaccine to target multiple HFMD viruses. In the neonatal mouse challenge model, this immunized milk exhibited extensive passive protection against oral infections caused by the three HFMD viruses. Compared to vaccines, this strategy may offer a rapid and broadly applicable approach to providing passive immunity for the prevention of HFMD, particularly in response to the swift emergence and spread of new variants.

Viruses associated with measles-like illnesses in Uganda

OBJECTIVES

In this study, we investigated the causes of measles-like illnesses (MLI) in the Uganda national surveillance program in order to inform diagnostic assay selection and vaccination strategies.

METHODS

We used metagenomic next-generation sequencing (M-NGS) on the Illumina platform to identify viruses associated with MLI (defined as fever and rash in the presence of either cough, coryza or conjunctivitis) in patient samples that had tested IgM negative for measles between 2010 and 2019.

RESULTS

Viral genomes were identified in 87/271 (32%) of samples, of which 44/271 (16%) contained 12 known viral pathogens. Expected viruses included rubella, human parvovirus B19, Epstein Barr virus, human herpesvirus 6B, human cytomegalovirus, varicella zoster virus and measles virus (detected within the seronegative window-period of infection) and the blood-borne hepatitis B virus. We also detected Saffold virus, human parvovirus type 4, the human adenovirus C2 and vaccine-associated poliovirus type 1.

CONCLUSIONS

The study highlights the presence of undiagnosed viruses causing MLI in Uganda, including vaccine-preventable illnesses. NGS can be used to monitor common viral infections at a population level, especially in regions where such infections are prevalent, including low and middle income countries to guide vaccination policy and optimize diagnostic assays.

Mucosal vaccines for viral diseases: Status and prospects

Virus-associated infectious diseases are highly detrimental to human health and animal husbandry. Among all countermeasures against infectious diseases, prophylactic vaccines, which developed through traditional or novel approaches, offer potential benefits. More recently, mucosal vaccines attract attention for their extraordinary characteristics compared to conventional parenteral vaccines, particularly for mucosal-related pathogens. Representatively, coronavirus disease 2019 (COVID-19), a respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), further accelerated the research and development efforts for mucosal vaccines by thoroughly investigating existing strategies or involving novel techniques. While several vaccine candidates achieved positive progresses, thus far, part of the current COVID-19 mucosal vaccines have shown poor performance, which underline the need for next-generation mucosal vaccines and corresponding platforms. In this review, we summarized the typical mucosal vaccines approved for humans or animals and sought to elucidate the underlying mechanisms of these successful cases. In addition, mucosal vaccines against COVID-19 that are in human clinical trials were reviewed in detail since this public health event mobilized all advanced technologies for possible solutions. Finally, the gaps in developing mucosal vaccines, potential solutions and prospects were discussed. Overall, rational application of mucosal vaccines would facilitate the establishing of mucosal immunity and block the transmission of viral diseases.

Trade-offs of different poliovirus vaccine options for outbreak response in the United States and other countries that only use inactivated poliovirus vaccine (IPV) in routine immunization

Delays in achieving polio eradication have led to ongoing risks of poliovirus importations that may cause outbreaks in polio-free countries. Because of the low, but non-zero risk of paralysis with oral poliovirus vaccines (OPVs), countries that achieve and maintain high national routine immunization coverage have increasingly shifted to exclusive use of inactivated poliovirus vaccine (IPV) for all preventive immunizations. However, immunization coverage within countries varies, with under-vaccinated subpopulations potentially able to sustain transmission of imported polioviruses and experience local outbreaks. Due to its cost, ease-of-use, and ability to induce mucosal immunity, using OPV as an outbreak control measure offers a more cost-effective option in countries in which OPV remains in use. However, recent polio outbreaks in IPV-only countries raise questions about whether and when IPV use for outbreak response may fail to stop poliovirus transmission and what consequences may follow from using OPV for outbreak response in these countries. We systematically reviewed the literature to identify modeling studies that explored the use of IPV for outbreak response in IPV-only countries. In addition, applying a model of the 2022 type 2 poliovirus outbreak in New York, we characterized the implications of using different OPV formulations for outbreak response instead of IPV. We also explored the hypothetical scenario of the same outbreak except for type 1 poliovirus instead of type 2. We find that using IPV for outbreak response will likely only stop outbreaks for polioviruses of relatively low transmission potential in countries with very high overall immunization coverage, seasonal transmission dynamics, and only if IPV immunization interventions reach some unvaccinated individuals. Using OPV for outbreak response in IPV-only countries poses substantial risks and challenges that require careful consideration, but may represent an option to consider for some outbreaks in some populations depending on the properties of the available vaccines and coverage attainable.

MA, Tovar-Rosero YY, Oñate AA, O'Ryan M. Two centuries of vaccination: historical and conceptual approach and future perspectives

Over the past two centuries, vaccines have been critical for the prevention of infectious diseases and are considered milestones in the medical and public health history. The World Health Organization estimates that vaccination currently prevents approximately 3.5-5 million deaths annually, attributed to diseases such as diphtheria, tetanus, pertussis, influenza, and measles. Vaccination has been instrumental in eradicating important pathogens, including the smallpox virus and wild poliovirus types 2 and 3. This narrative review offers a detailed journey through the history and advancements in vaccinology, tailored for healthcare workers. It traces pivotal milestones, beginning with the variolation practices in the early 17th century, the development of the first smallpox vaccine, and the continuous evolution and innovation in vaccine development up to the present day. We also briefly review immunological principles underlying vaccination, as well as the main vaccine types, with a special mention of the recently introduced mRNA vaccine technology. Additionally, we discuss the broad benefits of vaccines, including their role in reducing morbidity and mortality, and in fostering socioeconomic development in communities. Finally, we address the issue of vaccine hesitancy and discuss effective strategies to promote vaccine acceptance. Research, collaboration, and the widespread acceptance and use of vaccines are imperative for the continued success of vaccination programs in controlling and ultimately eradicating infectious diseases.

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.

Improvement of the qmosRT-PCR Assay and Its Application for the Detection and Quantitation of the Three Serotypes of the Novel Oral Polio Vaccine in Stool Samples

Recently, genetically stable novel OPVs (nOPV) were developed by modifying the genomes of Sabin viruses of conventional OPVs to reduce the risk of reversion to neurovirulence and therefore the risk of generating circulating vaccine-derived polioviruses. There is a need for specific and sensitive methods for the identification and quantification of nOPV viruses individually and in mixtures for clinical trials and potentially for manufacturing quality control and environmental surveillance. In this communication, we evaluated and improved the quantitative multiplex one-step reverse transcriptase polymerase chain reaction (qmosRT-PCR) assay for the identification and quantification of nOPV viruses in samples with different formulations and virus concentrations and in virus-spiked stool samples. The assay was able to specifically identify at least 1 log10 CCID50/mL of each serotype in the presence of the two other serotypes at high concentrations (6-7 log10 CCID50/mL) in the same sample. In addition, the lowest viral concentration that the assay was able to detect in stool samples was 17 CCID50/mL for nOPV1 and nOPV2 viruses and 6 CCID50/mL for nOPV3. We also found high correlation between the expected and observed (by qmosRT-PCR) concentrations of spiked viruses in stool samples for all three nOPV viruses, with R-squared values above 0.95. The analysis of samples collected from an nOPV2 clinical trial showed that 100% of poliovirus type 2 was detected and few samples showed the presence of type 1 and 3 residuals from previous vaccinations with bOPV (at least 4 weeks prior vaccination with nOPV2), confirming the high sensitivity of the method. The qmosRT-PCR was specific and sensitive for the simultaneous identification and quantification of all three nOPV viruses. It can be used as an identity test during the nOPV manufacturing process and in evaluation of virus excretion in nOPV clinical trials.

Oral polio vaccine stockpile modeling: insights from recent experience

BACKGROUND

Achieving polio eradication requires ensuring the delivery of sufficient supplies of the right vaccines to the right places at the right times. Despite large global markets, decades of use, and large quantity purchases of polio vaccines by national immunization programs and the Global Polio Eradication Initiative (GPEI), forecasting demand for the oral poliovirus vaccine (OPV) stockpile remains challenging.

RESEARCH DESIGN AND METHODS

We review OPV stockpile experience compared to pre-2016 expectations, actual demand, and changes in GPEI policies related to the procurement and use of type 2 OPV vaccines. We use available population and immunization schedule data to explore polio vaccine market segmentation, and its role in polio vaccine demand forecasting.

RESULTS

We find that substantial challenges remain in forecasting polio vaccine needs, mainly due to (1) deviations in implementation of plans that formed the basis for earlier forecasts, (2) lack of alignment of tactics/objectives among GPEI partners and other key stakeholders, (3) financing, and (4) uncertainty about development and licensure timelines for new polio vaccines and their field performance characteristics.

CONCLUSIONS

Mismatches between supply and demand over time have led to negative consequences associated with both oversupply and undersupply, as well as excess costs and potentially preventable cases.