Collaborative studies on the development of national reference standards for potency determination of H7N9 influenza vaccine

Establishment of Reference Reagents for Single-Radial-Immunodiffusion Assay on the 2022/23 Seasonal Influenza Vaccine in Japan and Their Quality Validation

Potency tests for influenza vaccines are currently performed using a single-radial immunodiffusion (SRID) assay, which requires a reference antigen and anti-hemagglutinin (HA) serum as reference reagents. Reagents must be newly prepared each time a strain used for vaccine production is modified. Therefore, establishing reference reagents of consistent quality is crucial for conducting vaccine potency tests accurately and precisely. Here, we established reference reagents for the SRID assay to conduct lot release tests of quadrivalent influenza vaccines in Japan during the 2022/23 influenza season. The potency of reference antigens during storage was confirmed. Furthermore, we evaluated the cross-reactivity of each antiserum raised against the HA protein of the 2 lineages of influenza B virus toward different lineages of influenza B virus antigens to select a suitable procedure for the SRID assay for accurate measurement. Finally, the intralaboratory reproducibility of the SRID assay using the established reference reagents was validated, and the SRID reagents had sufficient consistent quality, comparable to that of the reagents used for testing vaccines during previous influenza seasons. Our study contributes to the quality control of influenza vaccines.

The development of China's vaccine industry in the past decade: the perspective from drug regulatory science

Analysis of the batch issued data of Chinese vaccines from 2011 to 2020 showed that the average annual dose of vaccines in China was 769.66 million doses, and the overall production was stable. Fourteen new vaccines were added, six of which were developed in China. The batch issued dose of national immunization program (NIP) vaccine was stable with slightly decreased, while the non-NIP vaccine showed an increasing trend. The development trend of combined vaccine increased significantly. Regulatory science in China’s development, promoted the China’s vaccine regulation the perfection of legal system, and the steady improvement of vaccine quality and standards, and the gradual maturity of the construction of lot release system. With the goal of being safe, effective, reasonable, and accessible, China’s vaccines encourage the research and development of new technologies and emergency vaccines to constantly improve the level of public health.

H7N9 pandemic preparedness: A large-scale production of a split inactivated vaccine

In March 2013 it was reported by the World Health Organization (WHO) the first cases of human infections with avian influenza virus A (H7N9). From 2013 to December 2019, 1568 cases have been reported with 616 deaths. H7N9 infection has been associated with high morbidity and mortality rates, and vaccination is currently the most effective way to prevent infections and consequently flu-related severe illness. Developing and producing vaccines against pandemic influenza viruses is the main strategy for a response to a possible pandemic. This study aims to present the production of three industrial lots under current Good Manufacturing Practices (cGMP) of the active antigen used to produce the pandemic influenza vaccine candidate against A(H7N9). These batches were characterized and evaluated for quality standards and tested for immunogenicity in mice. The average yield was 173.50 ± 7.88 μg/mL of hemagglutinin and all the preparations met all the required specifications. The formulated H7N9 vaccine is poorly immunogenic and needs to be adjuvanted with an oil in water emulsion adjuvant (IB160) to achieve a best immune response, in a prime and in a boost scheme. These data are important for initial production planning and preparedness in the case of a H7N9 pandemic.

Influenza Virus Like Particles (VLPs): Opportunities for H7N9 Vaccine Development

In the midst of the ongoing COVID-19 coronavirus pandemic, influenza virus remains a major threat to public health due to its potential to cause epidemics and pandemics with significant human mortality. Cases of H7N9 human infections emerged in eastern China in 2013 and immediately raised pandemic concerns as historically, pandemics were caused by the introduction of new subtypes into immunologically naïve human populations. Highly pathogenic H7N9 cases with severe disease were reported recently, indicating the continuing public health threat and the need for a prophylactic vaccine. Here we review the development of recombinant influenza virus-like particles (VLPs) as vaccines against H7N9 virus. Several approaches to vaccine development are reviewed including the expression of VLPs in mammalian, plant and insect cell expression systems. Although considerable progress has been achieved, including demonstration of safety and immunogenicity of H7N9 VLPs in the human clinical trials, the remaining challenges need to be addressed. These challenges include improvements to the manufacturing processes, as well as enhancements to immunogenicity in order to elicit protective immunity to multiple variants and subtypes of influenza virus.

Development and characterization of standard reagents for cell-based prepandemic influenza vaccine products

Outbreaks of infection by novel avian influenza virus strains in humans cause public health issues worldwide, and the development of vaccines against such novel strains is the most effective method for the prevention of these virus outbreaks. All types of vaccines must be tested for potency before use; thus, quantitative potency assays are needed for influenza vaccines. The single radial immunodiffusion (SRID) assay is considered the gold standard for quantification of influenza virus antigens, and the SRID reference reagents are essential for the determination of vaccine potency. However, it remains debatable whether reference reagents derived from egg-based vaccine platforms can be used to precisely quantify non-egg-derived vaccines; thus, influenza vaccine production using cell-based platforms has attracted increasing attention. To evaluate the utility of reference reagents derived from a cell-based influenza vaccine platform, we prepared cell-based reference reagents from MDCK cell-grown viruses and compared them with egg-derived reference reagents. A primary liquid standard (PLS) was purified from cell-derived candidate influenza vaccine viruses, and hemagglutinin (HA) antigen content was determined by a densitometric method. The produced PLS could be stored at 4°C for more than 10 months. We also established a simple HA protein purification method for goat antiserum preparation, and the performance of the resulting antiserum was compared to that of standard reagents obtained using different production platforms. The results of this study indicate that these reference reagents can be used for both cell-based and egg-based production platforms and that the differences between these two types of platforms are negligible.

Process development for pandemic influenza VLP vaccine production using a baculovirus expression system

Background

Influenza viruses cause hundreds of thousands of respiratory diseases worldwide each year, and vaccination is considered the most effective approach for preventing influenza annual epidemics or pandemics. Since 1950, chicken embryonated eggs have been used as the main method for producing seasonal influenza vaccines. However, this platform has the main drawback of a lack of scale-up flexibility, and thus, egg-based vaccine manufacturers cannot supply sufficient doses within a short period for use for pandemic prevention. As a result, strategies for reducing the manufacturing time and increasing production capacity are urgently needed. Non-virion vaccine methods have been considered an alternative strategy against an influenza pandemic, and the purpose of maintaining an immunogenic capsule structure with infectious properties appears to be met by the virus-like particle (VLP) platform.

Results

An influenza H7N9-TW VLP production platform using insect cells, which included the expression of hemagglutinin (HA), NA, and M1 proteins, was established. To scale up H7N9-TW VLP production, several culture conditions were optimized to obtain a higher production yield. A high level of dissolved oxygen (DO) could be critical to H7N9-TW VLP production. If the DO was maintained at a high level, the HA titer obtained in the spinner flask system with ventilation was similar to that obtained in a shake flask. In this study, the HA titer in a 5-L bioreactor with a well-controlled DO level was substantially improved by 128-fold (from 4 HA units (HAU)/50 μL to 512 HAU/50 μL).

Conclusions

In this study, a multigene expression platform and an effective upstream process were developed. Notably, a high H7N9-TW VLP yield was achieved using a two-step production strategy while a high DO level was maintained. The upstream process, which resulted in high VLP titers, could be further used for large-scale influenza VLP vaccine production.

International Biological Reference Preparations for Epidemic Infectious Diseases

Recent years have seen unprecedented investment in research and development for countermeasures for high-threat pathogens, including specific and ambitious objectives for development of diagnostics, therapeutics, and vaccines. The inadequate availability of biological reference materials for these pathogens poses a genuine obstacle in pursuit of these objectives, and the lack of a comprehensive and equitable framework for developing reference materials is a weakness. We outline the need for internationally standardized biological materials for high-threat pathogens as a core element of global health security. We also outline the key components of a framework for addressing this deficiency.

Establishment of national reference for bunyavirus nucleic acid detection kits for diagnosis of SFTS virus

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) caused by SFTS virus (SFTSV) usually have a high fatality. At present no effective therapy or vaccine are available, so early diagnosis of SFTS is crucial to prevent and control SFTSV infection. This study aimed to establish a national reference for these diagnostic kits of SFTSV genome and make the diagnosis of the disease effective.

METHODS

Six SFTSV strains isolated from different regions, and five relative viruses with similar clinical manifestations were selected as positive and negative references and assessed using real time quantitative PCR (q-PCR) using specific primers and probe and two commercial kits. The stability of the references was also assessed at 37 °C, room temperature or -70 °C for 8 days, 14 days or 8 months respectively, or following several cycles of freezing-thawing. Collaborative calibration of the references was performed by three labs.

RESULTS

The references indicated good accuracy and specificity. The lowest detection limit was 10² U/mL. The accuracy was coefficient of variation less than 5%. The references were highly stable at high temperatures and after long storing and freezing-thawing treatment.

CONCLUSIONS

We successfully established a national reference with good accuracy, high specificity, sensitivity and stability, which can be applied for quality control of commercial SFTSV diagnostic kits, thus preventing and controlling SFTS.

TRIAL REGISTRATION

The references have been finished and it was retrospectively registered in the following article.

A novel approach for preparation of the antisera reagent for potency determination of inactivated H7N9 influenza vaccines

Background

The potency of inactivated influenza vaccines is determined using a single‐radial immunodiffusion (SRID) assay and requires standardized reagents consisting of a Reference Antigen and an influenza strain‐specific antiserum. Timely availability of reagents is a critical step in influenza vaccine production, and the need for backup approaches for reagent preparation is an important component of pandemic preparedness.

Objectives

When novel H7N9 viruses emerged in China in 2013, candidate inactivated H7N9 influenza vaccines were developed for evaluation in clinical trials, and reagents were needed to measure vaccine potency.

Methods

We previously described an alternative approach for generating strain‐specific potency antisera, utilizing modified vaccinia virus Ankara vectors to produce influenza hemagglutinin (HA)‐containing virus‐like particles (VLPs) for immunization. Vector‐produced HA antigen is not dependent upon the success of the traditional bromelain‐digestion and HA purification.

Results

Antiserum for H7N9 vaccines, produced after immunization of sheep with preparations of bromelain‐HA (br‐HA), was not optimal for the SRID assay, and the supply of antiserum was limited. However, antiserum obtained from sheep boosted with VLPs containing H7 HA greatly improved the ring quality in the SRID assay. Importantly, this antiserum worked well with both egg‐ and cell‐derived antigen and was distributed to vaccine manufacturers.

Conclusions

Utilizing a previously developed approach for preparing vaccine potency antiserum, we have addressed a major bottleneck encountered in preparation of H7N9 vaccine reagents. The combination of br‐HA and mammalian VLPs for sequential immunization represents the first use of an alternative approach for producing an influenza vaccine potency antiserum.