Final frontiers of the polio eradication endgame

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.

Cost minimization analysis of a hexavalent vaccine in Argentina

BACKGROUND

Argentina currently uses a pentavalent vaccine containing diphtheria, tetanus, pertussis (whole cell), Haemophilus influenza type b and hepatitis B antigens, administered concomitantly with the inactivated polio vaccine (IPV) (DTwP-Hib-HB plus IPV) in its childhood vaccination schedule. However, hexavalent vaccines containing acellular pertussis antigens (DTaP-Hib-HB-IPV) and providing protection against the same diseases are also licensed, but are only available with a private prescription or for high-risk pre-term infants in the public health program. We analyzed the cost of switching from the current schedule to the alternative schedule with the hexavalent vaccine in Argentina, assuming similar levels of effectiveness.

METHODS

The study population was infants ≤ 1 year of age born in Argentina from 2015 to 2019. The analysis considered adverse events, programmatic, logistic, and vaccine costs of both schemes from the societal perspective. The societal costs were disaggregated to summarize costs incurred in the public sector and with vaccination pre-term infants in the public sector. Costs were expressed in 2021 US Dollars (US$).

RESULTS

Although the cost of vaccines with the alternative scheme would be US$39.8 million (M) more than with the current scheme, these additional costs are in large part offset by fewer adverse event-associated costs and lower programmatic costs such that the overall cost of the alternative scheme would only be an additional US$3.6 M from the societal perspective. The additional cost associated with switching to the alternative scheme in the public sector and with the vaccination of pre-term infants in the public sector would be US$2.1 M and US$84,023, respectively.

CONCLUSIONS

The switch to an alternative scheme with the hexavalent vaccine in Argentina would result in marginally higher vaccine costs, which are mostly offset by the lower costs associated with improved logistics, fewer separate vaccines, and a reduction in adverse events.

Environmental surveillance for Salmonella Typhi as a tool to estimate the incidence of typhoid fever in low-income populations

Background: The World Health Organisation recommends prioritised use of recently prequalified typhoid conjugate vaccines in countries with the highest incidence of typhoid fever. However, representative typhoid surveillance data are lacking in many low-income countries because of the costs and challenges of diagnostic clinical microbiology. Environmental surveillance (ES) of Salmonella Typhi in sewage and wastewater using molecular methods may offer a low-cost alternative, but its performance in comparison with clinical surveillance has not been assessed. Methods: We developed a harmonised protocol for typhoid ES and its implementation in communities in India and Malawi where it will be compared with findings from hospital-based surveillance for typhoid fever. The protocol includes methods for ES site selection based on geospatial analysis, grab and trap sample collection at sewage and wastewater sites, and laboratory methods for sample processing, concentration and quantitative polymerase chain reaction (PCR) to detect Salmonella Typhi. The optimal locations for ES sites based on digital elevation models and mapping of sewage and river networks are described for each community and their suitability confirmed through field investigation. We will compare the prevalence and abundance of Salmonella Typhi in ES samples collected each month over a 12-month period to the incidence of blood culture confirmed typhoid cases recorded at referral hospitals serving the study areas. Conclusions: If environmental detection of Salmonella Typhi correlates with the incidence of typhoid fever estimated through clinical surveillance, typhoid ES may be a powerful and low-cost tool to estimate the local burden of typhoid fever and support the introduction of typhoid conjugate vaccines. Typhoid ES could also allow the impact of vaccination to be assessed and rapidly identify circulation of drug resistant strains.

Enabling accelerated vaccine roll-out for Public Health Emergencies of International Concern (PHEICs): Novel Oral Polio Vaccine type 2 (nOPV2) experience

To address the evolving risk of circulating vaccine-derived poliovirus type 2 (cVDPV2), Global Polio Eradication Initiative (GPEI) partners are working closely with countries to deploy an additional innovative tool for outbreak response - novel oral polio vaccine type 2 (nOPV2). The World Health Organization's (WHO) Prequalification program issued an Emergency Use Listing (EUL) recommendation for nOPV2 on 13 November 2020. The WHO's EUL procedure was created to assess and list unlicensed vaccines, therapeutics and diagnostics to enable their use in response to a Public Health Emergency of International Concern (PHEIC). nOPV2 was the first vaccine to receive an EUL, paving the way for other emergency vaccines. In this report, we summarise the pathway for nOPV2 roll-out under EUL.

VaxArray immunoassay for the multiplexed quantification of poliovirus D-antigen

Next generation poliovirus vaccines are critical to reaching global poliovirus eradication goals. Recent efforts have focused on creating inactivated vaccines using attenuated Sabin strains that maintain patient safety benefits and immunogenicity of conventional inactivated vaccines while increasing manufacturing safety and lowering production costs, and on developing novel oral vaccines using modified Sabin strains that provide critical mucosal immunity but are further attenuated to minimize risk of reversion to neurovirulence. In addition, there is a push to improve the analytical tools for poliovirus vaccine characterization. Conventional and Sabin inactivated poliovirus vaccines typically rely on standard plate-based ELISA as in vitro D-antigen potency assays in combination with WHO international standards as calibrants. While widely utilized, the current D-antigen ELISA assays have a long time to result (up to 72 h), can suffer from lab-to-lab inconsistency due to non-standardized protocols and reagents, and are inherently singleplex. For D-antigen quantitation, we have developed the VaxArray Polio Assay Kit, a multiplexed, microarray-based immunoassay that uses poliovirus-specific human monoclonal antibodies currently under consideration as standardized reagents for characterizing inactivated Sabin and Salk vaccines. The VaxArray assay can simultaneously quantify all 3 poliovirus serotypes with a time to result of less than 3 h. Here we demonstrate that the assay has limits of quantification suitable for both bioprocess samples and final vaccines, excellent reproducibility and precision, and improved accuracy over an analogous plate-based ELISA. The assay is suitable for adjuvanted combination vaccines, as common vaccine additives and crude matrices do not interfere with quantification, and is intended as a high throughput, standardized quantitation tool to aid inactivated poliovirus vaccine manufacturers in streamlining vaccine development and manufacturing, aiding the global polio eradication effort.

•

Multiplexed D-antigen immunoassay for all 3 poliovirus serotypes

•

Has <3 h time to result and compares well to 3-day plate-based ELISA

•

Assay shows high specificity and is reactive to sIPV, cIPV, and OPV

•

Applicable to in-process samples, final IPV and combination vaccine formulations

•

High accuracy and precision for both sIPV and cIPV over multiple users and days

Preferences of Persons with or at Risk for Hepatitis C for Long-Acting Treatments

BACKGROUND

Whereas safe, curative treatments for hepatitis C virus (HCV) have been available since 2015, there are still 58 million infected persons worldwide, and global elimination may require new paradigms. We sought to understand the acceptability of long-acting HCV treatment approaches.

METHODS

A cross-sectional, 43-question survey was administered to 1457 individuals with HCV or at risk of HCV at 28 sites in 9 countries to assess comparative interest in a variety of long-acting strategies in comparison to oral pills.

RESULTS

Among HCV-positive participants, 37.7% most preferred an injection, 5.6% an implant, and 6% a gastric residence device, as compared to 50.8% who stated they would most prefer taking 1 to 3 pills per day. When compared directly to taking pills, differences were observed in the relative preference for an injection based on age (p<0.001), location (p<0.001), and prior receipt of HCV treatment (p=0.005), but not sex. When an implant was compared to pills, greater preference was represented by women (p=0.01) and adults of younger ages (p=0.012 per 5 years). Among participants without HCV, 49.5% felt that injections are stronger than pills, and 34.7% preferred taking injections to pills. Among those at-risk participants who had received injectable medications in the past, 123 out of 137 (89.8%) expressed willingness to receive one in the future.

CONCLUSIONS

These data point to high acceptability of long-acting treatments, which for a substantial minority, might even be preferred to pills for the treatment of HCV infection. Long-acting treatments for HCV infection might contribute to global efforts to eliminate hepatitis C.

Plasma cell immunoglobulin heavy chain repertoire dynamics before and after tetanus booster vaccination

Antibody sequence repertoire analysis of plasma cells (PC) isolated before and 1 week after a vaccine provides time-specific snapshots of the antibody response. Comparison of the immunoglobulin (Ig) sequences pre- and post-vaccination allows analysis of maturation over time and identification of antigen specific Ig. Here we compare the Ig heavy chain (Ig-H) repertoire of circulating PCs isolated from 10⁹ peripheral blood mononuclear cells (PBMC) collected by apheresis 1 week after a tetanus toxoid vaccine booster with the Ig-H repertoire of PCs collected 2 and 11 weeks prior to the booster. A total of 21,060 unique Ig nucleotide sequences encoding 14,307 unique heavy chain complementarity determining region 3 (CDR-H3) amino acid sequences, also called clonotypes, were identified. Only 466 clonotypes (3.3%) were present at all 3 time points. In contrast, 90% of the 30 highest frequency CDR-H3 regions at +1w were also identified at another time point and 50% were present at all time points, suggesting the rapid expansion of a memory B cell population. The tetanus toxoid specificity of the CDR-H3 region with the 7th highest frequency at +1w was confirmed using immunoprecipitation and mass spectroscopy, and two public tetanus toxoid-specific CDR-H3 regions were also overrepresented at +1w. In summary, we have used the tetanus vaccine model system to demonstrate that bulk PC Ig repertoire analysis can identify PC populations that expand and mature following antigen exposure. The application of this approach before and after clinical infections should advance our understanding of clinical protection and facilitate vaccine design.

The bumpy road to achieve herd immunity in COVID-19

Herd immunity is a form of indirect protection that is offered to the community when a large proportion of individuals contained in the community are immune to a certain infection. This immunity can be due to vaccination or to the recovery post-disease. Effective herd immunity in SARS-CoV-2 infection has several hurdles upon achievement. Herd immunity cannot be obtained concomitantly in many geographical areas because the areas have different population density and the societal measures to contain the spreading are different. A proportion of 50-66% of the population needs to be immunized naturally or artificially in this SARS-Cov2 pandemic and this percentage is not easily achievable. The duration of herd immunity is another issue while information on the long-term immune response against SARS-CoV2 is yet scarce. Epitope stability, another issue to be solved when achieving herd immunity, is important. Mutation in the viral structure will call upon other sets of neutralizing antibodies and hence for other herd immunity type installment. The societal tactics to achieve the much-needed herd immunity should be developed keeping in mind the welfare of the population. Without being exhaustive, throughout our paper we will elaborate on each of the hurdles encountered in developing herd immunity to SARS-Cov2 infection.