mRNA Vaccines: Key Considerations For Development & Manufacturing

Advances in biotechnology have led to a new generation of vaccine treatments entering development and trial. These innovations include the use of genetically modified organisms and the development of vaccines based on mRNA, where human cells are programmed to develop antibodies against specific diseases. While these vaccines appear new to the general public, research dates back several decades.

As with any pharmaceutical development, there are technical challenges and regulatory hurdles. Balanced with the possibility of the types of serious illnesses that can be addressed, a careful path needs to be followed in terms of meeting regulatory expectations, developing mRNA vaccines, and getting products to the market speedily.¹

The types of issues that need to be assessed and planned for include meeting CGMP requirements, process validation, comparability, stability, post-approval changes, release testing, and packaging, each of which is connected to the manufacturing and quality control of vaccines. This article looks at mRNA vaccine manufacturing challenges and bottlenecks and how they are addressed. The time-to-market will be based on how effectively pharmaceutical companies address the developmental challenges.

Development Challenges

mRNA vaccines can, theoretically, be produced rapidly, and the field has been advanced through immunogenicity and efficacy.² However, there are various factors to consider; developing vaccines is not straightforward, given relatively high failure rates and high time and monetary costs required to establish the complex processes and production capabilities.³

The development of any biotechnological product is fraught with difficulties and misdirection. With mRNA vaccines, the main obstacles faced by developers are arguably:

• Unintended effects: With patient safety, a risk arises that the mRNA strand contained within the vaccine could elicit an unintended immune reaction (particularly inflammation and autoimmune reactions). To address this, a key focus of development is on creating mRNA vaccine sequences that precisely mimic those produced by human cells.
• Delivery: The effective action of a vaccine rests on the mechanism of delivery. The complexity arises because when the mRNA enters the human body, it is rapidly broken down. Hence, stabilization is essential to protect the mRNA strand until it reaches its target. The strategy involves incorporating the mRNA within a larger molecule. This can be enhanced by further containment within particles or liposomes (spherical vesicles composed of lipid bilayers). For the COVID-19 vaccines, the mRNA is protected by nanoparticles.
  • A further delivery consideration is finding the most effective way for mRNA to reach the cell. For the vaccine to be effective, mRNA must penetrate the barrier of the lipid membrane in order to reach the cytoplasm to be translated into functional protein.⁴
• Storage: Most vaccines are limited by their storage time (stability) and required holding temperatures. Currently, mRNA vaccines require storage within a freezer or refrigerator, which will affect their global distribution. Developing vaccines that do not rely on cold supply chains will significantly increase their applicability. Some studies are looking into lyophilization as an ambient storage method.

A further challenge is with process validation. The standard regulatory requirement is for full-scale batches to be produced. Given the scarcity of the material and the urgent need (in most cases) for vaccines, adopting a risk-based strategy based on ICH Q9 to show equivalent validation at a smaller scale is required, together with obtaining regulatory agreement. This can be supported by applying process analytical technology to provide real-time results to feed into a continuous validation paradigm. The core objective is to demonstrate the consistency of the manufacturing process. As the characterization of mRNA technology continues, adopting a risk-based approach can be advanced, provided that different biotechnology companies are prepared to share knowledge.

Development of a vaccine needs to be planned according to the principles of quality by design and quality risk management. Consideration must be given to the design space and the design of experiments.

Overcoming these challenges requires a combination of knowledge capture, scientific reasoning, learning from data analysis, and risk-based methodologies.

Long-Term Safety And Effectiveness

Another hurdle with mRNA vaccine development is ensuring safety. mRNA has been associated with inhibition of antigen expression and may negatively affect the immune response. Other safety concerns include local and systemic inflammation, stimulation of auto-reactive antibodies, and toxic effects of any non-native nucleotides and delivery system components (triggering inflammation and autoimmunity). Each of these needs to be demonstrably overcome during the drug development phase.

Regarding effectiveness, demonstrating the stability of the mRNA vaccine is important given that degradation by both enzymatic and chemical pathways can occur.⁵ Effectiveness is also hampered by a lack of experience in mass vaccination using mRNA vaccines – despite the success of COVID-19 vaccines – and this means understanding the relative effectiveness is currently limited across time and geographically.

Clinical Trials

In order to prove efficacy, mRNA vaccine research needs to lead to clinical trials. As well as demonstrating efficacy against the specific pathogen, trials need to establish the stability of the vaccine and the optimal method for delivery (such as intramuscular, intravenous, nasal, and others). Currently, these types of data are limited, and longer-term trial data are required. Widely sharing the knowledge from trials among pharmaceutical companies will help move mRNA vaccines forward. Furthermore, in pandemic situations, space should open up to enable accelerated clinical development, again adopting a risk-based approach together with regulatory dialogue.

Synthesis

The scientific evaluation of manufacturing and laboratory data, together with clinical trial results, must demonstrate that the overall benefits of the vaccine outweigh their risks, including any side effects. This information must also be provided to regulators, including all testing against approved specifications and any associated investigations.

Production

There are many trial mRNA vaccines in development. What has yet to be tested, aside from the COVID-19 vaccines, is production to scale. It is currently uncertain, in many cases, how effectively production methods can be scaled up to enable mass production. Purification is essential to the production process, as several steps will be required to remove reaction components. The more steps required, the lower the resultant yield.⁶

Some the components, such as polymerases and capping enzymes, are only available in limited volumes and many have a high cost, meaning that many companies examining mRNA vaccines require seed funding to keep afloat during the development phase.

Good Manufacturing Practices

Many supply chain requirements can be met by making the necessary enzymes and reaction components available from commercial vendors. Since these are generally synthesized chemicals and bacterially expressed (hence, animal component-free) reagents, many of the safety concerns that affect conventional cell-culture-based vaccine manufacture are avoided.⁷

Important GMP controls include:

• Multistep protocols
• Patient safety controls
• Product potency controls
• Contamination control, including sterility

For the scale-up, adherence to GMP becomes more important and a suitable quality control strategy and an effective contamination control strategy need to be developed so manufacturing processes and plants meet current good manufacturing practice (cGMP). Ensuring the suitability of plants requires assessing potential risks and taking appropriate actions.⁸

With quality control, this will include the selection of each component used in the manufacturing process, starting with raw materials; intermediate testing; and an assessment of the finished product. The approach to quality control needs to be holistic and sufficient to understand the whole manufacturing process. The types of samples selected and tests undertaken must connect with the process validation strategy, where critical quality attributes and critical process parameters will have been identified so that process capability and manufacturing consistency can be understood. Given that quality cannot be established simply by end-product testing, each step of a manufacturing process must be controlled.

For the contamination control strategy, because the end product is designed to be sterile, sufficient assurance of sterility needs to be built into the manufacturing process supported by microbiological monitoring at suitable control points. The strategy should shape the aseptic filling design space.

The ease of meeting GMPs would be advanced should global regulatory harmonization occur, especially between the FDA and the European Medicines Agency. This topic will be expanded upon in a separate article.

Regulatory Approval

To obtain approval for the vaccine, the pharmaceutical company must also show that large-scale commercial manufacturing produces vaccines of the required quality. This requires the place of manufacture to have been licensed for this purpose and for process validation to be performed.⁹ Most regulators have special committees of experts in vaccination to assess new vaccines. The regulator will assess:

• whether the vaccine meets rigorous standards for safety, efficacy, and quality;
• if the vaccine is manufactured and controlled in approved, certified facilities; and
• that pharmaceutical standards are compatible with large-scale commercialization.

Time can also be saved when there is early and continuous dialogue between vaccine manufacturers and regulators.

In certain circumstances, regulators will elect to fast-track vaccines, such as in the event of a public health emergency. A recent example of this was with the COVID-19 vaccines.¹⁰ The fast-track process involves covering all phases of development but undertaking these in a compressed time. The application of scientific knowledge and previous experience in vaccine production is essential for the faster process.

Some regulators also permit a rolling review process for certain medicines. Under these conditions, the regulator may agree to start assessing data as they become available during the development process. This helps to expedite the approval process. Similarly, some manufacturers can also gain approval to commence manufacturing prior to obtaining marketing authorization. This enables vaccines to be distributed quickly once regulatory authorization has been obtained.

Release Of Commercial Batches

The test release process must include an assessment of all tests used in the process validation and these must be assessed against the product specification. In some territories, such as Europe, an official medicines control laboratory must perform an additional independent control test for each batch of vaccine. This acts as a compliance check of the manufacturer’s own test results.

Pharmacovigilance

Pharmacovigilance requires that vaccine safety for use in real life is assessed across the shelf-life of the released product. Continued scientific and clinical evaluation needs to take place to assess how effective the vaccine continues to be in protecting people against diseases and to note any adverse events. To maintain patient safety, the benefits must continue to outweigh any potential risks.

A system for safety monitoring and risk management needs to be in place, with measures in place for:

• Providing advice to minimize risk.
• Reporting suspected side effects.
• Detecting any potential side effects.
• Conducting rigorous scientific assessments of all safety data.
• Introducing any necessary mitigating actions in the event of adverse events.

Summary

New medicinal products and mRNA vaccines, specifically, face the complexities and challenges of development and scale-up, meeting cGMP, and the process of securing regulatory approval. These challenges include the difficulties involving mRNA stability and creating an effective delivery system. This article considers how these can be addressed by adopting a scientific and risk-based approach. Addressing these issues is important to pave the way for more mRNA vaccines to enter the medicines market.

References

1. Pardi N. et al. mRNA vaccines - a new era in vaccinology. Nat Rev Drug Discov. 2018; 17(4): 261-279
2. Bahl, K. et al. Preclinical and clinical demonstration of immunogenicity by mRNA vaccines against H10N8 and H7N9 influenza viruses. Mol. Ther. 2017; 25, 1316–1327
3. Médecins Sans Frontières. The Right Shot: Bringing down barriers to affordable and adapted vaccines, 2nd ed.; 2015 https://cdn.doctorswithoutborders.org/sites/usa/files/attachments/the_right_shot_2nd_edition.pdf
4. Benteyn, D. et al. mRNA-based dendritic cell vaccines. Expert Rev. Vaccines, 2015; 14, 161–176
5. Muralidhara, B. K. et al. Critical considerations for developing nucleic acid macromolecule based drug products. Drug Discov. Today, 2016; 21, 430–444
6. Robinson, J. Vaccine production: main steps and considerations. In Bloom, B. and Lambert, P. (Eds.) The vaccine book (2nd ed.), Academic Press, San Diego (2016), pp. 77-96
7. Pardi, N. et al. In vitro transcription of long RNA containing modified nucleosides. Methods Mol. Biol. 2013; 969, 29–42
8. Silva, A. et al Advances in Vaccines, Current Applications of Pharmaceutical Biotechnology. 2020; 171: 155–188
9. Wijnans, L. and Voordouw, B. A review of the changes to the licensing of influenza vaccines in Europe. Influenza and Other Respiratory Viruses. 2015; 10 (1): 2–8
10. Bok, K. et al. Accelerated COVID-19 vaccine development: milestones, lessons, and prospects. Immunity, 2021; 54 (8): 1636–1651

About The Author:

Tim Sandle, Ph.D., is a pharmaceutical professional with wide experience in microbiology and quality assurance. He is the author of more than 30 books relating to pharmaceuticals, healthcare, and life sciences, as well as over 170 peer-reviewed papers and some 500 technical articles. Sandle has presented at over 200 events and he currently works at Bio Products Laboratory Ltd. (BPL), and he is a visiting professor at the University of Manchester and University College London, as well as a consultant to the pharmaceutical industry. Visit his microbiology website at https://www.pharmamicroresources.com.