COVID-19 vaccine development during pandemic: gap analysis, opportunities, and impact on future emerging infectious disease development strategies

ABSTRACT

The world remains cautiously optimistic about a COVID-19 vaccine that is relatively safe and efficacious and that offers sufficient long-lasting protection/immunity by neutralizing the virus infectivity. However, key technical hurdles pertaining to antigen-adjuvant formulation, delivery, and manufacturing challenges of lipid nanoparticles (LNPs) for mRNA vaccines and stability of formulations need to be addressed for successful product development and stockpiling. In addition, the dosage form, the dosage level and regimen for eliciting a protective immune response remain to be established. The high dependence of global supply chains and demand-supply to sourcing quality raw materials, glassware and other supplies, along with the stress on existing production capacities and platform-specific manufacturing challenges could impede vaccine development and access. This article provides critical analysis of vaccine development processes and unit operations that can derail the pandemic response, and also extends to other emerging infectious disease development efforts – issues that take on added significance given the global mandate for an accelerated and at-risk development path to tackle the COVID-19 pandemic.

The development and deployment of vaccines and other treatment modalities in epidemic settings have exposed the gaps in existing global healthcare systems, global emergency preparedness, response and deployment, manufacturing, and related supply chains.¹ Rapid and significant Federal and nonprofit investments have incentivized multiple pharma and biotech companies, outsourcing contract development and manufacturing organizations (CDMOs), raw material and supply chain vendors, and academia to accelerate, mobilize, and conduct priority research to meet the global demand of producing billions of doses of safe and effective vaccine(s) to protect against the global COVID (SARS-Cov-2) pandemic.

Vaccine development process is complex and time-consuming, and needs significant funding, human capital, and expertise. To tackle the pandemic, the typical vaccine development paradigm has been substituted by a fast-track approach with compressed development activities and manufacturing timelines and expanding existing capacities at risk (Figure 1).^2,3,4 Understanding the translational scalability and cGMP manufacturability readiness of innovative platforms, processes, and products and if it can deliver on the principle of meeting the pandemic goals of producing billions of doses of a safe and relatively effective COVID vaccine is a significant unknown.^2,5

Figure 1.

Schematic comparing typical vaccine development process paradigm with potential expedited manufacturing at risk for pandemics. The current vaccine categories are: (i) inactivated virus, (ii) replicating and non-replicating viral vectors, (iii) nucleic acid vaccine (DNA and mRNA), (iv) recombinant protein vaccines and (v) virus like particles.⁶ [A] Traditional vaccine development pathway and activities; [B] Traditional vaccine development pathway to licensure; [C] Pandemic Paradigm: Overlapping phases and shortening development time. (Figure not as per time scale)

Abbreviations: BDS: bulk drug substance; CQA: critical quality attributes; CMO: Contract Manufacturing organization; CTM: Clinical trial material; DP: Drug product; Eng. Run: Engineering run (batch); GMP: Good Manufacturing Practice; IND: Investigational new drug Phase app. Mfg: Phase appropriate manufacturing; PD: Process development; POC: Proof of Concept; QA: Quality Assurance; QC: Quality Control.

As per WHO, 26 experimental vaccines against the novel coronavirus are in clinical evaluation with 6 candidates moving into the final phase of testing.⁶ Given the scientific claims and the medical optimism about acceleration of COVID vaccines and technologies, the current article raises some key issues and risks regarding technological, scale-up, manufacturing, and supply chain operations that can impede COVID vaccine product development, global distribution, and access. The relevance of the challenges extend beyond the COVID pandemic and the key underpinnings are directly applicable to other emerging infectious disease global development and countermeasure efforts.

1. The adjuvant and formulation conundrum

An adjuvanted vaccine can trigger activation of the innate system and induce an enhanced immune response and improved efficacy while substantially reducing the amount of vaccine amount needed per dose (dose sparing) thereby offering more doses and reducing the cost of a vaccine. For the vaccine field in general, access to proprietary and clinically approved adjuvant systems remains a challenge. In partnership and funding from CEPI, adjuvant makers such as GSK/AS03 adjuvant, Sequeris-CSL/MF59 emulsion, and Dynavax/TLR9 CpG 1018 are committed to providing billion doses of adjuvants to their collaborators. However, the compatibility and stability of these adjuvanted vaccines and the effectiveness of the immune response elicited by these adjuvanted protein vaccines remains undetermined. While each product innovator is committed to one of the adjuvant system, the lack of head-to-head comparison between antigens and adjuvant systems in early clinical settings could potentially create false positives regarding the efficacy of a vaccine candidate. A more prudent clinical evaluation that compares side-by-side the immune response (and safety) generated by individual protein antigen in permutation and combination with clinically relevant adjuvants is required. While preliminary results in animals and healthy volunteers in Phase 1 trials appear promising, the lack of desired efficacy and immune response (and protection) in COVID-infected patients from any of the advanced Phase 2/3 clinical trials, will set the field back, as one may not be able to account for and distinguish the functional potency of the immune response due to wrong antigen-adjuvant combination/formulation, or suboptimal antigen design or wrong adjuvant selection.

For a total global population of ~7.8 billion people, estimated global demand for vaccines totaled 3.5 billion doses in 2018.⁷ In a pandemic, assuming 100% vaccination, with a minimum of two doses per person (prime and booster dose) the number of vaccine doses will be ~2-2.5X higher (~16-20 billion doses) assuming some overage of doses for stockpiling. For 75% coverage = ~12-15 billion doses; for 60% coverage = ~10-12 billion doses of vaccines will be required globally to tackle the COVID pandemic. While the current commitment from some of the adjuvant makers stands for 1-2 billion doses, it remains unclear what is the long-term availability of these adjuvants to match the protein doses as well as support additional doses and additional vaccine regimens for pandemic response. Significantly, the pressure on the raw material supply chain and the quality of these raw materials required to produce the adjuvants could compromise the access and consistent formulation and production process vis-à-vis the commitments to existing global product pipelines these adjuvants already support.

While the push and preference have been to use proprietary adjuvants, the under-utilization or no use of alum (GMP grade alum is cheap), which is used in majority of licensed prophylactic vaccines, is indicative of a foregone conclusion (and assumption) by the scientific community without any supporting data, that alum adjuvanted COVID vaccine formulations won't elicit the desired immune response while other TLR agonist adjuvant formulations would. If alum as an adjuvant is used, do the funding authorities know if the appropriate quality and sterilized alum (Adjuphos, Alhydrogel, Rehydragel) stockpile available to support the pandemic response? Should early investigational clinical trials with various adjuvants be benchmarked atleast against alum? The failure of the recent HIV efficacy trial HVTN-702 due to lack of immune response and efficacy in comparison to the benchmark RV-144 trial (~30% efficacy) has been sobering news for the vaccine field and has raised more questions than answers.⁸ While the Phase 2b/3 efficacy trial was advanced based on prior immune responses observed in an earlier Phase 1 trial, the striking differences between RV-144 and HVTN 702 trial were the use of different adjuvants (inorganic Rehydragel alum vs. MF59 organic emulsion), differences in drug product (DP) formulation, modified immunogens, and differences in vaccination regimen.

While the pandemic response is advancing at high risk, the non-existent preclinical data with respect to antigen-adjuvant formulation development and its effect on correlates of protection, the compatibility of antigen-adjuvant mixtures, the degree of binding of antigen to adjuvant, long-term stability and storage of adjuvanted vaccine product can negatively impact the vaccine development, access, supply chain logistics, and deployment. Making clinically relevant adjuvants accessible to a broader group of product developers in the future will remain a challenge and will require further federal/non-profit incentivization with dedicated financing for public–private partnerships.

2. mRNA vaccines – the lipid nanoparticle (LNP) delivery challenge

Currently, there is no licensed mRNA or DNA vaccine which has generated a safe and effective immune response. Globally, atleast 18 mRNA vaccines are undergoing preclinical and clinical testing including Moderna mRNA-1273 (Phase 3), Pfizer/Biontech (Phase 3), Curevac (Phase 1) vaccine candidates, and others.⁶ The flexibility and cost benefits offered by mRNA platform are tremendous including relative ease of mRNA cGMP manufacturing over cell line production process for proteins, adaptability to various targets, and high number of doses of vaccine. However, the significant challenge for successful realization of this approach is critically dependent on the lipid nanoparticle (LNP) delivery system. The LNP consists of positively charged ionizable lipid that facilitates encapsulation of the large mRNA construct and combined with other delivery components, constitutes for ~95% of the vaccine composition, dose, and potential reactogenicity. Bringing these components together is possibly the most complex production step in the development of mRNA COVID vaccine. Typically, LNPs are made of four components, viz., the positively charged proprietary lipid, phosphatidylcholine lipid (helper lipid), cholesterol, and polyethylene glycol–lipid conjugate combined with the mRNA in a specific stoichiometry. Critical to the success of GMP manufacturing of mRNA-LNP vaccine is the ability to consistently produce reproducible batches of the vaccine at the desired scales affording a reasonably stable mRNA-LNP vaccine formulation. Slight variation in the manufacturing process parameters (mixing speed, ratio of fluids, pH, temperature, hold times, shear pressure), production scale (batch sizes), and the design configuration of manufacturing vessels can dramatically influence the formulation process, particle morphology, particle size/charge, and potency of the LNP vaccine. Combining the aforementioned reasons with the raw material product quality (type of lipids, physicochemical attributes, purity/impurity profile), can trigger batch-to-batch and particle size variability, product heterogeneity, stability issues, and product-specific critical quality attribute failures that can affect the quality and performance of final mRNA-LNP vaccine drug product (DP) resulting in production delays. Additionally, at higher scales, purification and sterilization process can pose unique problems related to the integrity and structure of LNPs thereby resulting in batch failures which will impact the final dose, dosage form and critical quality attributes of the vaccine.

The proprietary nature of the ionizable lipid component of the LNP system remains a pain point of litigation, IP, licensing/sub-licensing, and exclusivity issues and has been overlooked. This aspect requires extreme scrutiny and can potentially derail global vaccine access based on who owns the IP for the lipid (and the process) and who has the freedom to operate.⁹ Authorities also need to ensure that the vaccine companies cost sharing and financial risk (royalties and other payments) in billions of dollars are not transferred and imposed upon the federal/nonprofit agencies and tax-payers.

Not much information is available in print media or in publications regarding the differences in mRNA-LNP vaccine candidates that make it unique and differentiating from each other and why each warrants independent clinical testing. In addition, not much information is available about either the dose of LNP, the differentiating type (and similarity) of the lipids, the composition of LNPs and the ability of LNPs to potentiate any kind of adjuvant/reactogenic effect. The impact of the low dose of PEG in PEG-conjugated lipid in mRNA-LNP formulations to stimulate anti-PEG response in prophylactic mRNA-LNP vaccines and its role in induction of accelerated blood clearance (ABC) will need more clarity.¹⁰

It also remains unclear if the sourcing supply chain partners can meet the demand and supply of high quality and controlled GMP-grade individual raw materials required for LNP fabrication and to stockpile to support the ongoing (and future) multiple production campaigns or will it require manufacturing new batches of these individual components.

The understanding of these advanced LNP platforms, processes, and chemistry is a complex, not fully understood and is a niche expertise which many of the global CDMOs may lack and will require expertise beyond the confines of more traditional therapies, cell line development, scale and GMP production. While existing capacities may be suitable for Phase 1 (and possibly Phase 2), they may not have the manufacturing fit suitable for pandemic production and will require additional design modifications, capacity building prior to vaccine production.

3. Vialed drug product, dosage form, stability, and storage

Manufacturing processes that produce a high yielding purified bulk product will dictate the number of doses available, the overall cost of goods, and the pricing of the vaccine. While this data is forthcoming based on ongoing clinical trials, currently, the lack of information about the final vaccine dose amount (and adjuvant) per vial and dosage form that will stimulate efficacy and long-lasting/sufficient protection could significantly delay the fill/finish operation of the bulk drug substance (BDS) to vialed DP. In the case of recombinant protein vaccine, the manufacturing scales, capacity and doses will also have to align with the availability of adjuvant(s) for equal doses, mixing and formulation of the bulk vaccine with adjuvant for the final drug product. Prior to product release, a key aspect of the recombinant protein production process from cell lines is controlling the levels and removal of viral contamination and host cell proteins in the final BDS, which are process impurities via various downstream unit operations (low-pH inactivation, virus filtration, and chromatographic purifications).

The stability of the various COVID vaccine drug products is currently undisclosed. This is interconnected to the development of an optimized formulation and cold chain storage ensuring antigen compatibility and stability with the adjuvant or LNPs or the pH/buffers/excipients used for formulation. The protein vaccines or DNA vaccines can be stable for atleast 4 years (at 4°C) while mRNA-LNP vaccines (typically stored at −80°C) can be more sensitive to temperature variations, prone to lipid oxidation/degradation and integrity changes, increase in particle size and polydispersity, particle aggregation, loss of potency that can adversely affect the safety or efficacy of the mRNA-LNP vaccine. If ineffective, lyophilization of mRNA-LNP vaccine with appropriate cryoprotectants/excipients may have to be assessed if it allows for easy reconstitution without affecting the critical quality attributes including potency and can offer long-term cold storage stability option. However, addition of lyophilization step extends the timeline and adds significant cost to the mRNA-LNP vaccine production process.

Finally, not much is also known about the ideal vaccine dosage form or if the vaccine will be a multi-antigen vaccine and if it will be stored at frozen or at 4°C. These aspects gain significance from a cold chain and stockpiling point of view, as the stability window (product expiry) and vaccine testing/analytics to measure product degradation over a period of time become critical factors in supply and availability, which will dictate how soon new batches of product doses will have to be manufactured and restocked in order to minimize the drug shortage or the severity of a shortage.

4. Multiantigen vaccines

Ideally one would prefer a single vaccine (monovalent) with 2–3 doses stimulating neutralizing Abs and long-lasting protective immunity against COVID. However, contingent on the ongoing clinical study results, it is equally likely that the final COVID vaccine may require and consist of a multi-antigen DP to acquire durable and long-term antibody responses. As such, the final product presentation could be a monovalent vaccine, single vial multivalent recombinant protein vaccine (with adjuvant), or multi-vial vaccine DPs with heterologous prime boost immunization regimen strategy (priming with one class of antigen followed by a booster shot of different antigen). A multi-antigen mRNA vaccine candidate will have to face practical formulation development and product release challenges in addition to issues related to clinical safety and tolerability that may arise due to significant amount of LNP given per dose. Similarly, a single vial of multi-antigen protein vaccine is a changed product configuration (from single antigen) and will require addressing issues related to formulation and multi-antigen-adjuvant compatibility, analytical QC control and product release, short/long-term stability, vial configuration, fine-tuning of the optimal dose of adjuvant and in vivo immune interference as a function of multiple antigens. Multi-antigen vaccine development is often underappreciated and can be a complex endeavor and given the current unknowns and the evolving nature of the virus, one remains hopeful that the information generated from some of the advanced clinical trials will inform regarding the efficacy and protection offered by the products and the possible permutation and combination of vaccines, the immunization regimen, and administration that may be required in the future.

At this stage, critical questions regarding the correlates of protection, efficacy-based surrogate markers and the levels of protective immune response required remain unsettled. This is further complicated by limited understanding of D614G mutation on the spike protein¹¹ and other evolving strains (antigen drift and shift across continents) and the role of glycosylation in protective immunity and induction of neutralizing/functional Abs. If the monovalent vaccines being tested will offer broad cross protection against the existing and potential evolving new SARS-Cov-2 strains remains to be seen.

5. Outsourcing pressures and translation of advanced platform technologies

One of the key caveats of advanced platform technologies or disruptive technologies is them being not sufficiently mature for broad-based deployment and throughput to cover a large number of vaccinations for a rapid public health campaign. Till this goal is achieved in addition to the clinical efficacy endpoints, some of these advanced technologies and devices may remain experimental proof-of-concept studies.

Specifically, the burden on the global capacity and suppliers to provide column resins for individual downstream unit operations, GMP raw materials for LNP production, glass/steel vessels and appropriate configurations to fit within the existing manufacturing suites and availability of glass vial and stopper configurations for fill finish activities/capacities or injectable syringes across the globe vis-à-vis an already committed clientele advancing other biologics and therapeutic modalities including monoclonal Abs and high demand for cell and gene therapy products can potentially delay pandemic vaccine and therapeutic production and testing efforts.⁵ In case of select DNA vaccines (Inovio vaccine candidate), the use of electroporation devices for vaccination (over traditional intramuscular immunizations) needs further understanding from patient compliance point of view and the fabrication scale at which these devices will have to be manufactured, deployed, and distributed globally for more than billion doses. For adenovirus vector vaccine (such as Oxford/Astrazeneca candidate) which typically uses transient transfection process in the initial phases of development, will have to be translated to a more robust, consistently scalable, and controllable production and purification process and overcome the barriers for GMP production, testing and commercialization.

Phase appropriate manufacturing will require different partners at different phases of clinical development and commercial production. Partners suitable for Phase 1 activities may not be appropriate for commercialization purposes. Furthermore, some of the contract development and manufacturing organizations (CDMOs) will have to surge capacity using existing infrastructure and need procurement and installation of new glassware/vessels, tanks, large BDS storage containers for increasing capacity, and modify existing design configurations. This will indeed test the phase-appropriateness cGMP, quality assurance, and platform-specific readiness and expertise of the various CDMOs.

The global footprint of technology transfer activities and transfer of materials including proprietary and complex production unit operations and processes, assays, and appropriate documentation etc. will have to occur seamlessly.

BDS storage and shipping for fill finish activities are other critical endeavors that has to be monitored. Majority of the CDMOs operate at full capacity and depending on their size/capacity may not have the prerequisite surge capacities to tackle emergency preparedness and onsite fill-finish capabilities/operations. This can trigger a bottleneck in clinical development due to the limited number of appropriate fill-finish sites and the number of vials required for Phase 2 and 3 trials and beyond.

6. Age-related vaccination and regulatory path

The age-related decline in immunity results not only in increased susceptibility to infection but also reduces the prophylactic efficacy of vaccination. Whether the level of efficacy and protection offered by all the experimental vaccines being tested in various clinical trials is uniform across all age groups or varies with different age groups and geographic locations will indicate if the vaccines have to be tailored to address efficacy in older populations and remains unknown at this stage.

There is global consensus that flexibility and scalability are key in rapid response to an emerging infectious disease threat. While the FDA’s willingness to grant fast track clinical evaluation and emergency use authorizations, without compromising on the product safety and quality are met, has to be lauded, how the agencies current flexibility and intent to expedite the regulatory process (while still being rigorous and with no increased patient safety risk) influences future clinical development plans for advancing other vaccines and biologics vis-à-vis the risk tolerances and benefits of the products remains to be seen.

In conclusion, emerging infectious diseases will continue to emerge/reemerge and reshape emergency preparedness response and medical countermeasures in the coming years. The key points discussed in this article will remain critical for defining the global vaccine product development strategies and pandemic preparedness with a realistic timeframe in mind to tackle outbreaks of this magnitude. In the interim, the world remains cautiously optimistic about the promise of billion doses of COVID-19 vaccine or vaccine(s) to treat the pandemic that is safe, efficacious, and offers sufficient long-lasting protection/immunity by neutralizing the virus.

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.