Evaluation of the genotype I Japanese encephalitis virus as a stable viral vector for foreign gene expression

Manipulation of the flavivirus genome to accommodate and express a heterologous gene of interest has become an attractive approach for gene delivery and the development of viral-vectored vaccines. However, due to the inherent genetic instability of the flavivirus genomes, the construction of recombinant viruses carrying a foreign gene could be problematic and heavily resistant. In this study, the possibility of the Japanese encephalitis virus (JEV) as a stable flavivirus vector for the expression of a foreign gene was assessed using reverse genetics. The full-length cDNA genome of genotype I (GI) JEV inherently possessed excellent stability and manipulability in a bacterial host, while mutations and deletions accumulated in the cDNA genomes of genotype Ⅲ (GⅢ) JEV strains. Using the GI JEV as backbones, we generate a panel of recombinant viruses expressing various foreign genes. All recombinant viruses exhibited excellent genetic stability and efficiently express foreign genes for at least ten serial passages in vitro. In application, a convenient, rapid and reliable image-based assay for neutralizing antibody testing and antiviral drug discovery was established with a mCherry-reporter recombinant virus (rBJ-mCherry). Meanwhile, the recombinant viruses expressing the antigens of the African swine fever virus (ASFV) or Classical swine fever virus (CSFV) could effectively induce antibody responses to the JEV vector and foreign antigens in a mouse vaccination model. Therefore, GI JEV strains could serve as viral vectors accommodating the expression of large foreign genes.

Flexible analytic model to inform multi-stakeholder pediatric vaccine scheduling decisions

BACKGROUND

Pediatric immunization is important for preventing potentially life-threatening diseases in children. Over time, the number of recommended pediatric vaccines has increased and is likely to increase further as new vaccines are developed. Given the different number of doses for available vaccines and various constraints (e.g., the appropriate age for each dose of a vaccine or the time between doses), it is challenging to develop a recommended vaccination schedule or a catch-up schedule when a child falls behind on one or more vaccinations.

METHODS

We developed an integer programming optimization model, enabled by Python programming and embedded into an Excel-based decision tool, to recommend childhood vaccination schedules or personalized catch-up schedules. The model recommends a vaccination schedule that balances the goal of being as close as possible to the clinically-indicated dosing schedules and the goal of minimizing clinic visits, and gives users the ability to trade off between these two goals. We illustrated the broad applicability of our proposed model with commonly-faced vaccine scheduling challenges in the United States.

RESULTS

The illustrative computational case study confirms our model's ability to create personalized schedules based on each child's age and vaccination history, and to adjust appropriately when a new vaccine becomes available.

CONCLUSIONS

The model presented in this paper fills the need for an easy-to-use tool to recommend vaccination schedules for de novo and catch-up purposes. It provides straightforward recommendations that can be easily used by physicians, is flexible to handle the requirements varying by region, and can be updated as new vaccines are approved for use.

Proposal for the revision of guidelines for clinical trials of vaccines to prevent infectious diseases in Japan

The development of vaccines against infectious diseases requires a different approach from that of therapeutics, because vaccines are inoculated into healthy individuals and have a preventive effect by activating the immunity of the inoculated human. In Japan, "The Guideline for Clinical Trials of Vaccines for the Prevention of Infectious Diseases" was published in 2010 before changes occurred in the vaccine development environment in Japan, such as the introductions of foreign vaccines and simultaneous global development. This study aimed to identify current challenges in vaccine development through a questionnaire-based survey of pharmaceutical companies in Japan and by comparing the domestic and international guidelines and surveying review reports of 35 vaccines approved in Japan between April 2010 and December 2020. Identified challenges included the requirement for protective efficacy trials, efficacy evaluation of combination vaccines, development of multiregional and foreign clinical trials, and immunization of older adults and immunocompromised patients. We propose that new vaccines against infectious diseases should be evaluated for the protective efficacy, preferably through multiregional clinical trials. Additionally, differences in the incidence of infectious diseases or in epidemic virus strains between regions may affect the trials, when multiregional clinical trials are conducted, but immunogenicity-based studies can be conducted if a correlation between protective efficacy and immunogenicity has been established. We suggest that licensed combination vaccines can be used as comparators when an antigen is added to a licensed combination vaccine. We also proposed that the efficacy of a vaccine in non-major subjects, such as older adults or immunocompromised patients could be evaluated by comparing immunogenicity in major subjects with the confirmed protective effects of the vaccine. It is expected that these revisions will lead to the rapid advancement of vaccine development, which should contribute to the improvement of public health.

Economic assessment of incorporating the hexavalent vaccine as part of the National Immunization Program of Peru

Background

This study aimed to estimate the economic impact of replacing the current Peruvian primary immunization scheme for infants under 1 year old with an alternative scheme with similar efficacy, based on a hexavalent vaccine.

Methods

A cost-minimization analysis compared the costs associated with vaccine administration, adverse reactions medical treatment, logistical activities, and indirect social costs associated with time spent by parents in both schemes. A budgetary impact analysis assessed the financial impact of the alternative scheme on healthcare budget.

Results

Incorporating the hexavalent vaccine would result in a 15.5% net increase in healthcare budget expenditure ($48,281,706 vs $55,744,653). Vaccination costs would increase by 54.1%, whereas logistical and adverse reaction costs would be reduced by 59.8% and 33.1%, respectively. When including indirect social costs in the analysis, the budgetary impact was reduced to 8.7%. Furthermore, the alternative scheme would enable the liberation of 17.5% of national vaccines storage capacity.

Conclusions

Despite of the significant reduction of logistical and adverse reaction costs, including the hexavalent vaccine into the National Immunization Program of Peru in place of the current vaccination scheme for infants under 1 year of age would increase the public financial budget of the government as it would represent larger vaccine acquisition costs. Incorporating the indirect costs would reduce the budgetary impact demonstrating the social value of the alternative scheme. This merits consideration by government bodies, and future studies investigating such benefits would be informative.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-022-08006-1.

DTaP combination vaccine use and adherence: A retrospective cohort study

Despite universal recommendation of the 4-dose diphtheria, tetanus, and pertussis (DTaP) vaccine series, coverage and timeliness in the US remain suboptimal. DTaP-containing combination vaccines (i.e. quadrivalent and pentavalent) are presumed to improve vaccine coverage rates and timeliness, but research supporting this claim is limited. We sought to investigate the associations between DTaP-containing vaccine use and adherence to the recommended DTaP immunization schedule among children in the US. Using a large claims database, we identified privately insured children born between 2009 and 2016 that received ≥1 DTaP-containing vaccine and had ≥24 months of enrollment from birth, excluding those with DTaP vaccinations not aligned with approved dose indications. Children were classified by DTaP-containing vaccine receipt: combination vaccines only, stand-alone vaccines only, or a mixture of both. Outcome measures included: 1) completion of the 4-dose series and 2) timely receipt of doses. Outcomes were adjusted for gender, birth year, race, and socioeconomic status. The study cohort contained 412,441 children. Of these, 40.5% (167,084) received combination vaccines only, 14.9% (61,342) received stand-alone vaccines only, and 44.6% (184,015) received a mixture of both. Combination vaccine recipients were nearly 3 times as likely to complete the 4-dose series (OR 2.93 (95% CI: 2.88, 2.99)) and for all doses received, more than 4 times as likely to receive doses on time (OR 4.12 (4.04, 4.21), relative to stand-alone vaccine recipients. Significance disparities in adherence were also observed, where minorities were up to 30% less likely (OR 0.70 (0.68, 0.71)) to complete the 4-dose series and up to 27% less likely (OR 0.73 (0.72, 0.75)) to receive doses on time, relative to white children. Our findings demonstrated that adherence to the recommended DTaP immunization schedule was significantly greater among combination vaccine recipients, relative to stand-alone recipients. Further research is needed to investigate underlying causes of disparities in adherence.

A single immunogenicity assay for testing potency of combination DTaP vaccines: Simultaneous quantitation of anti-DT, anti-TT, anti-PTxd and anti-FHA antibodies in Guinea-pig serum with a Luminex®-xMAP® bead-based serological assay

The diphtheria toxoid (DT), tetanus toxoid (TT), and acellular pertussis (aP) single immunogenicity assay (DTaP SIA) is a Luminex®-xMAP®-bead-based multiplex immunoassay for estimating the potency of DTaP pediatric combination vaccines in guinea pigs. This manuscript describes the validation of this assay for the simultaneous quantitation of anti-diphtheria toxoid (anti-DT), anti-tetanus toxoid (anti-TT), anti-pertussis toxoid (anti-PTxd), and anti-filamentous hemagglutinin (anti-FHA) antibodies in guinea pig serum following injection of a DTaP vaccine formulation. The results were expressed in arbitrary units/mL (AU/mL) using reference serum for comparison. Specificity was demonstrated by ≥ 75% homologous and ≤25% heterologous inhibition for all the antigens. The results were linear for anti-DT, anti-TT, anti-PTxd and anti-FHA antibodies. Accuracy was demonstrated with recovery of between 80% and 120% for all four antibodies. The relative standard deviation of repeatability was ≤20%. The results demonstrate that this SIA can be used for the linear, accurate, and precise simultaneous detection of all four antibodies, based on both the ICH Q2 and the EMA guidelines on bioanalytical method validation.

Development and validation of magnetic bead pentaplex immunoassay for simultaneous quantification of murine serum IgG antibodies to acellular pertussis, diphtheria and tetanus antigens used in combination vaccines

We describe here a magnetic bead-based multiplex (pentaplex) immunoassay (MIA) platform developed as an alternative to enzyme-linked immunosorbent assays (ELISA) used in immunogenicity testing of DTaP/TdaP vaccine in animals. MIA simultaneously measures the concentration of serum (IgG) antibodies against B. Pertussis antigens; pertussis toxin, filamentous hemagglutinin (FHA), pertactin (PRN) and tetanus (T) and diphtheria (D) toxoid in the Tdap vaccine immunized animals. Assay validation experiments were done using a panel of serum samples. The results are expressed in IU/ml using WHO reference mice serum. The standard curve was linear with 4PL logistic fit over an eight 2-fold dilution range with LOQ of 0.003, 0.022, 0.005 IU/ml for PT, FHA and PRN and 0.016 U/ml for T and D antigens indicating sensitivity. No interference was observed in monoplex versus multiplex measurements. Specificity was demonstrated by ≥90% homologous and ≤15% heterologous inhibition for all the antigens. The assay was reproducible, with a mean coefficient of variation (CV) of ≤10% for intra-assay duplicates and ≤25% for interassays using different lots of beads and analyst. Accuracy was demonstrated wherein the ratio of observed vs. assigned unitages were within 80-120%. The study suggests that the Pentaplex (MIA) platform meets all the criteria for the serological assay combination vaccines with additional advantages of high throughput, reduced sample volumes, faster analysis with reduced manpower in contrast to conventional monoplex ELISA.

Hexavalent vaccines: characteristics of available products and practical considerations from a panel of Italian experts

Combination vaccines represent a valuable technological innovation in the field of infectious disease prevention and public health, because of their great health and economic value from the individual, societal, and healthcare system perspectives. In order to increase parents' and healthcare professionals' confidence in the vaccination programs and maintain their benefits to society, more information about the benefits of innovative vaccination tools such as combination vaccines is needed. Purpose of this work is an examination of available hexavalent vaccines, that protect against Diphtheria, Tetanus, Pertussis, Poliomyelitis, Hepatitis B and Haemophilus influenzae type b infections. From the epidemiological updates of vaccine preventable diseases to the vaccine development cycle, from the immunogenicity of antigenic components to the safety and co-administration with other vaccines, several aspects of available hexavalent vaccines are discussed and deepened. Also a number of practical considerations on schedules, age of employment, strategies for vaccination recovery, vaccination in at-risk births are issued, based on the recommendations of Italian Ministry of Health, Italian Society of Pharmacology (SIF), Italian Society for Pediatrics (SIP), Italian Federation of Family Paediatricians (FIMP) and Italian Society of Hygiene, Preventive Medicine and Public Health (SItI).

New perspectives for hexavalent vaccines

With the increase in the number of routine vaccinations the development of pentavalent and hexavalent combination vaccines fitting the routine vaccination schedules became a necessity. In this respect, Europe has taken the lead in comparison with other world regions, and routine vaccination with pentavalent and hexavalent combinations including DTPa, Hib, HepB and IPV has been on European vaccination programs for >15years. Since the marketing authorization of Hexavac® and Infanrix Hexa® in 2000, immunization schedules in most European countries have included hexavalent vaccines. In the last years, two new hexavalent vaccines have been licensed and commercialized worldwide. This paper presents a review of the pharmaceutical profiles of the three hexavalent vaccines currently available. In addition, we aim to review safety, co-administration, tolerability and other practical concerns of their use.

The preparation and characterization of PLG nanoparticles with an entrapped synthetic TLR7 agonist and their preclinical evaluation as adjuvant for an adsorbed DTaP vaccine

The design of safe and potent adjuvants able to enhance and modulate antigen-specific immunity is of great interest for vaccine research and development. In the present study, negatively charged poly(lactide-co-glycolide) (PLG) nanoparticles have been combined with a synthetic immunepotentiator molecule targeting the Toll-like receptor 7. The selection of appropriate preparation and freeze-drying conditions resulted in a PLG-based adjuvant with well-defined and stable physico-chemical properties. The adjuvanticity of such nanosystem has later been evaluated in the mouse model with a diphtheria-tetanus-pertussis (DTaP) vaccine, on the basis of the current need to improve the efficacy of acellular pertussis (aP) vaccines. DTaP antigens were adsorbed onto PLG nanoparticles surface, allowing the co-delivery of TLR7a and multiple antigens through a single formulation. The entrapment of TLR7a into PLG nanoparticles resulted in enhanced IgG and IgG2a antibody titers. Notably, the immune potentiator effect of TLR7a was less evident when it was used in not-entrapped form, indicating that co-localization of TLR7a and antigens is required to adequately stimulate immune responses. In conclusion, the rational selection of adjuvants and formulation here described resulted as a highly valuable approach to potentiate and better tailor DTaP vaccine immunogenicity.

Combination Vaccines

Infections are still a leading cause of morbidity and mortality in children under five years of age, most of which can be prevented by vaccination. However, there are too many vaccines to be administered, increasing the cost of immunization and visits to the paediatrician. Combination vaccines can be an answer to these problems till the development of a single vaccine containing all the possible antigens. Researchers are aiming at development of an ideal vaccine, which can be given orally at birth, has negligible side effects, is heat stable and is affordable to all the parents.