An Application of an Initial Full Value of Vaccine Assessment Methodology to Measles-Rubella MAPs for Use in Low- and Middle-Income Countries.

Measles and rubella micro-array patches (MR-MAPs) are a promising innovation to address limitations of the current needle and syringe (N&S) presentation due to their single-dose presentation, ease of use, and improved thermostability. To direct and accelerate further research and interventions, an initial full value vaccine assessment (iFVVA) was initiated prior to MR-MAPs entering phase I trials to quantify their value and identify key data gaps and challenges. The iFVVA utilized a mixed-methods approach with rapid assessment of literature, stakeholder interviews and surveys, and quantitative data analyses to (i) assess global need for improved MR vaccines and how MR-MAPs could address MR problem statements; (ii) estimate costs and benefits of MR-MAPs; (iii) identify the best pathway from development to delivery; and (iv) identify outstanding areas of need where stakeholder intervention can be helpful. These analyses found that if MR-MAPs are broadly deployed, they can potentially reach an additional 80 million children compared to the N&S presentation between 2030-2040. MR-MAPs can avert up to 37 million measles cases, 400,000 measles deaths, and 26 million disability-adjusted life years (DALYs). MR-MAPs with the most optimal product characteristics of low price, controlled temperature chain (CTC) properties, and small cold chain volumes were shown to be cost saving for routine immunization (RI) in low- and middle-income countries (LMICs) compared to N&S. Uncertainties about price and future vaccine coverage impact the potential cost-effectiveness of introducing MR-MAPs in LMICs, indicating that it could be cost-effective in 16-81% of LMICs. Furthermore, this iFVVA highlighted the importance of upfront donor investment in manufacturing set-up and clinical studies and the critical influence of an appropriate price to ensure country and manufacturer financial sustainability. To ensure that MR-MAPs achieve the greatest public health benefit, MAP developers, vaccine manufacturers, donors, financiers, and policy- and decision-makers will need close collaboration and open communications.

A review of potential use cases for measles-rubella, measles-mumps-rubella, and typhoid-conjugate vaccines presented on microarray patches.

As an innovative vaccine delivery technology, vaccine microarray patches could have a meaningful impact on routine immunization coverage in low- and middle-income countries, and vaccine deployment during epidemics and pandemics. This review of the potential use cases for a subset of vaccine microarray patches in various stages of clinical development, including measles-rubella, measles-mumps-rubella, and typhoid conjugate, highlights the breadth of their applicability to support immunization service delivery and their potential scope of utilization within national immunization programs. Definition and assessment of the use cases for this novel vaccine presentation provide important insights for vaccine developers and policymakers into the strengths of the public health and commercial value propositions, and the preparatory requirements for public health systems for the future rollout of vaccine microarray patches. An in-depth understanding of use cases for vaccine microarray patches serves as a foundational input to overcoming the remaining technical, regulatory, and financial challenges. Additional efforts will help to realize the potential of vaccine microarray patches as part of the global effort to improve the coverage and equity of national immunization programs.

Impact and cost-effectiveness of measles vaccination through microarray patches in 70 low-income and middle-income countries: mathematical modelling and early-stage economic evaluation.

BACKGROUND: Microarray patches (MAPs) are a promising technology being developed to reduce barriers to vaccine delivery based on needles and syringes (N&S). To address the evidence gap on the public health value of applying this potential technology to immunisation programmes, we evaluated the health impact on measles burden and cost-effectiveness of introducing measles-rubella MAPs (MR-MAPs) in 70 low-income and middle-income countries (LMICs). METHODS: We used an age-structured dynamic model of measles transmission and vaccination to project measles cases, deaths and disability-adjusted life-years during 2030-2040. Compared with the baseline scenarios with continuing current N&S-based practice, we evaluated the introduction of MR-MAPs under different measles vaccine coverage projections and MR-MAP introduction strategies. Costs were calculated based on the ingredients approach, including direct cost of measles treatment, vaccine procurement and vaccine delivery. Model-based burden and cost estimates were derived for individual countries and country income groups. We compared the incremental cost-effectiveness ratios of introducing MR-MAPs to health opportunity costs. RESULTS: MR-MAP introduction could prevent 27%-37% of measles burden between 2030 and 2040 in 70 LMICs, compared with the N&S-only immunisation strategy. The largest health impact could be achieved under lower coverage projection and accelerated introduction strategy, with 39 million measles cases averted. Measles treatment cost is a key driver of the net cost of introduction. In countries with a relatively higher income, introducing MR-MAPs could be a cost-saving intervention due to reduced treatment costs. Compared with country-specific health opportunity costs, introducing MR-MAPs would be cost-effective in 16%-81% of LMICs, depending on the MR-MAPs procurement prices and vaccine coverage projections. CONCLUSIONS: Introducing MR-MAPs in LMICs can be a cost-effective strategy to revitalise measles immunisation programmes with stagnant uptake and reach undervaccinated children. Sustainable introduction and uptake of MR-MAPs has the potential to improve vaccine equity within and between countries and accelerate progress towards measles elimination.

Exploring potential applications of measles and rubella microarray patches (MR-MAPs): use case identification.

Introduction: Innovative vaccine products will be critical in helping to address the existing implementation barriers that have prevented the achievement of the measles and rubella (MR) vaccine coverage targets. Overcoming those barriers will be necessary to achieve the "Immunization Agenda 2030" goals. Microarray patches (MAPs), an innovative needle-free delivery device currently in clinical development, can be a potential game changer in this respect and contribute to the equitable delivery of vaccines in low- and middle-income countries and pandemic preparedness and response. Developing in-depth knowledge of the most desired and impactful uses of MRMAPs can prove critical to identifying the critical attributes of the target product profile, informing policy and adoption decisions, and helping to evaluate the potential public health and economic value of this technology. The first step in this process is the definition of the potential use cases for MR-MAPs, i.e., where and how this product is most likely to be used within the immunization programme. Methods: By applying a design-based user-centric approach, we implemented a three-step process, including a desk review, a survey, and interviews, to define the most relevant use cases for MR MAPS. Results: Six use cases have been identified as relevant across all different countries and immunization programme designs and validated by experts. Discussion: The identified use cases have already informed the demand estimate for MR-MAPs and provided the foundation for developing an initial full vaccine value assessment. We believe that, in the future, they will be highly valuable in ensuring that the roll-out of this promising innovation is designed in a way that maximizes the impact, particularly in populations and countries that are most in need.

Accelerating the development of vaccine microarray patches for epidemic response and equitable immunization coverage requires investment in microarray patch manufacturing facilities.

INTRODUCTION: There is a need for investment in manufacturing for vaccine microarray patches (vMAPs) to accelerate vMAP development and access. vMAPs could transform vaccines deployment and reach to everyone, everywhere. AREAS COVERED: We outline vMAPs' potential benefits for epidemic preparedness and for outreach in low- and lower-middle-income countries (LMICs), share lessons learned from pandemic response, and highlight that investment in manufacturing-at-risk could accelerate vMAP development. EXPERT OPINION: Pilot manufacturing capabilities are needed to produce clinical trial material and enable emergency response. Funding vMAP manufacturing scale-up in parallel to clinical proof-of-concept studies could accelerate vMAP approval and availability. Incentives could mitigate the risks of establishing multi-vMAP manufacturing facilities early.

Accelerating the Development of Measles and Rubella Microarray Patches to Eliminate Measles and Rubella: Recent Progress, Remaining Challenges.

Measles and rubella microarray patches (MR-MAPs) are critical in achieving measles and rubella eradication, a goal highly unlikely to meet with current vaccines presentations. With low commercial incentive to MAP developers, limited and uncertain funding, the need for investment in a novel manufacturing facility, and remaining questions about the source of antigen, product demand, and regulatory pathway, MR-MAPs are unlikely to be prequalified by WHO and ready for use before 2033. This article describes the current progress of MR-MAPs, highlights challenges and opportunities pertinent to MR-MAPs manufacturing, regulatory approval, creating demand, and timelines to licensure. It also describes activities that are being undertaken by multiple partners to incentivise investment in and accelerate the development of MR-MAPs.

Estimating the future global dose demand for measles-rubella microarray patches.

Background: Progress toward measles and rubella (MR) elimination has stagnated as countries are unable to reach the required 95% vaccine coverage. Microarray patches (MAPs) are anticipated to offer significant programmatic advantages to needle and syringe (N/S) presentation and increase MR vaccination coverage. A demand forecast analysis of the programmatic doses required (PDR) could accelerate MR-MAP development by informing the size and return of the investment required to manufacture MAPs. Methods: Unconstrained global MR-MAP demand for 2030-2040 was estimated for three scenarios, for groups of countries with similar characteristics (archetypes), and four types of uses of MR-MAPs (use cases). The base scenario 1 assumed that MR-MAPs would replace a share of MR doses delivered by N/S, and that MAPs can reach a proportion of previously unimmunised populations. Scenario 2 assumed that MR-MAPs would be piloted in selected countries in each region of the World Health Organization (WHO); and scenario 3 explored introduction of MR-MAPs earlier in countries with the lowest measles vaccine coverage and highest MR disease burden. We conducted sensitivity analyses to measure the impact of data uncertainty. Results: For the base scenario (1), the estimated global PDR for MR-MAPs was forecasted at 30 million doses in 2030 and increased to 220 million doses by 2040. Compared to scenario 1, scenario 2 resulted in an overall decrease in PDR of 18%, and scenario 3 resulted in a 21% increase in PDR between 2030 and 2040. Sensitivity analyses revealed that assumptions around the anticipated reach or coverage of MR-MAPs, particularly in the hard-to-reach and MOV populations, and the market penetration of MR-MAPs significantly impacted the estimated PDR. Conclusions: Significant demand is expected for MR-MAPs between 2030 and 2040, however, efforts are required to address remaining data quality, uncertainties and gaps that underpin the assumptions in this analysis.

Strategies for vaccine-product innovation: Creating an enabling environment for product development to uptake in low- and middle-income countries.

Vaccine-product innovations that address barriers to immunization are urgently needed to achieve equitable vaccine coverage, as articulated in the new Immunization Agenda 2030 and the Gavi 5.0 strategy. In 2020, the Vaccine Innovation Prioritisation Strategy (VIPS) prioritized three innovations, namely microarray patches (MAPs), heat-stable and controlled-temperature chain (CTC) enabled liquid vaccine formulations and barcodes on primary packaging. These innovations were prioritized based on the priority immunization barriers that they may help overcome in resource constrained contexts, as well as by considering their potential impact on health, coverage and equity, safety, economic costs and their technical readiness and commercial feasibility. VIPS is now working to accelerate the development and lay the foundation for future uptake of the three priority vaccine-product innovations, with the long term-goal to ensure equitable vaccine coverage and increased impact of vaccines in low- and middle- income countries. To inform our strategic planning, we analyzed four commercially available vaccine product-innovations and conducted interviews with individuals from 17 immunization organizations, and/or independent immunization experts. The findings are synthesized into an 'innovation conundrum' that describes the challenges encountered in developing vaccine-product innovations and a vaccine-product innovation 'theory of change', which highlights actions that should be undertaken in parallel to product development to incentivize sustainable investment and prepare the pathway for uptake and impact.

Development of a thermostable spray dried outer membrane vesicle pertussis vaccine for pulmonary immunization.

Worldwide resurgence of whooping cough calls for improved, next-generation pertussis vaccines that induce broad and long-lasting immunity. A mucosal pertussis vaccine based on outer membrane vesicles (omvPV) is a promising candidate. Further, a vaccine that is stable outside the cold chain would be of substantial advantage for worldwide distribution and application. A vaccine formulated as a powder could both stabilize the vaccine as well as make it suitable for pulmonary vaccination. To that end, we developed a spray dried omvPV with improved stability compared to the liquid omvPV formulation. Spray drying did not affect the structural integrity of the omvPV. The antigenicity of Vag8, a major antigen in omvPV was diminished slightly and an altered tryptophan fluorescence indicated some changes in protein structure. However, when administered via the pulmonary route in mice after reconstitution, spray dried omvPV showed comparable immune responses and protection against challenge with live B. pertussis as liquid omvPV. Mucosal IgA and Th17 responses were established in addition to broad systemic IgG and Th1/Th17 responses, indicating the induction of an effective immunity profile. Overall, a spray dried omvPV was developed that maintained effective immunogenic properties and has an improved storage stability.

The effect of formulation on spray dried Sabin inactivated polio vaccine.

The objective of this study was to develop a stable spray dried formulation, containing the three serotypes of Sabin inactivated polio vaccine (sIPV), aiming for minimal loss of native conformation (D-antigen) during drying and subsequent storage. The influence of atomization and drying stress during spray drying on trivalent sIPV was investigated. This was followed by excipient screening, in which monovalent sIPV was formulated and spray dried. Excipient combinations and concentrations were tailored to maximize both the antigen recovery of respective sIPV serotypes after spray drying and storage (T = 40 °C and t = 7 days). Furthermore, a fractional factorial design was developed around the most promising formulations to elucidate the contribution of each excipient in stabilizing D-antigen during drying. Serotype 1 and 2 could be dried with 98% and 97% recovery, respectively. When subsequently stored at 40 °C for 7 days, the D-antigenicity of serotype 1 was fully retained. For serotype 2 the D-antigenicity dropped to 71%. Serotype 3 was more challenging to stabilize and a recovery of 56% was attained after drying, followed by a further loss of 37% after storage at 40 °C for 7 days. Further studies using a design of experiments approach demonstrated that trehalose/monosodium glutamate and maltodextrin/arginine combinations were crucial for stabilizing serotype 1 and 2, respectively. For sIPV serotype 3, the best formulation contained Medium199, glutathione and maltodextrin. For the trivalent vaccine it is therefore probably necessary to spray dry the different serotypes separately and mix the dry powders afterwards to obtain the trivalent vaccine.

Whole-Inactivated Influenza Virus Is a Potent Adjuvant for Influenza Peptides Containing CD8+ T Cell Epitopes.

Influenza peptide antigens coding for conserved T cell epitopes have the capacity to induce cross-protective influenza-specific immunity. Short peptide antigens used as a vaccine, however, often show poor immunogenicity. In this study, we demonstrate that whole-inactivated influenza virus (WIV) acts as an adjuvant for influenza peptide antigens, as shown by the induction of peptide-specific CD8+ T cells in HLA-A2.1 transgenic mice upon vaccination with the influenza-M1-derived GILGFVFTL peptide (GIL), formulated with WIV. By screening various concentrations of GIL and WIV, we found that both components contributed to the GIL-specific T cell response. Whereas co-localization of the peptide antigen and WIV adjuvant was found to be important, neither physical association between peptide and WIV nor fusogenic activity of WIV were relevant for the adjuvant effect of WIV. We furthermore show that WIV may adjuvate T cell responses to a variety of peptides, using pools of either conserved wild-type influenza peptides or chemically altered peptide ligands. This study shows the potential of WIV as an adjuvant for influenza peptides. The simple formulation process and the solid safety record of WIV make this an attractive adjuvant for T cell peptides, and may also be used for non-influenza antigens.

Developments in the formulation and delivery of spray dried vaccines.

Spray drying is a promising method for the stabilization of vaccines, which are usually formulated as liquids. Usually, vaccine stability is improved by spray drying in the presence of a range of excipients. Unlike freeze drying, there is no freezing step involved, thus the damage related to this step is avoided. The edge of spray drying resides in its ability for particles to be engineered to desired requirements, which can be used in various vaccine delivery methods and routes. Although several spray dried vaccines have shown encouraging preclinical results, the number of vaccines that have been tested in clinical trials is limited, indicating a relatively new area of vaccine stabilization and delivery. This article reviews the current status of spray dried vaccine formulations and delivery methods. In particular it discusses the impact of process stresses on vaccine integrity, the application of excipients in spray drying of vaccines, process and formulation optimization strategies based on Design of Experiment approaches as well as opportunities for future application of spray dried vaccine powders for vaccine delivery.

Intranasal and sublingual delivery of inactivated polio vaccine.

Polio is on the brink of eradication. Improved inactivated polio vaccines (IPV) are needed towards complete eradication and for the use in the period thereafter. Vaccination via mucosal surfaces has important potential advantages over intramuscular injection using conventional needle and syringe, the currently used delivery method for IPV. One of them is the ability to induce both serum and mucosal immune responses: the latter may provide protection at the port of virus entry. The current study evaluated the possibilities of polio vaccination via mucosal surfaces using IPV based on attenuated Sabin strains. Mice received three immunizations with trivalent sIPV via intramuscular injection, or via the intranasal or sublingual route. The need of an adjuvant for the mucosal routes was investigated as well, by testing sIPV in combination with the mucosal adjuvant cholera toxin. Both intranasal and sublingual sIPV immunization induced systemic polio-specific serum IgG in mice that were functional as measured by poliovirus neutralization. Intranasal administration of sIPV plus adjuvant induced significant higher systemic poliovirus type 3 neutralizing antibody titers than sIPV delivered via the intramuscular route. Moreover, mucosal sIPV delivery elicited polio-specific IgA titers at different mucosal sites (IgA in saliva, fecal extracts and intestinal tissue) and IgA-producing B-cells in the spleen, where conventional intramuscular vaccination was unable to do so. However, it is likely that a mucosal adjuvant is required for sublingual vaccination. Further research on polio vaccination via sublingual mucosal route should include the search for safe and effective adjuvants, and the development of novel oral dosage forms that improve antigen uptake by oral mucosa, thereby increasing vaccine immunogenicity. This study indicates that both the intranasal and sublingual routes might be valuable approaches for use in routine vaccination or outbreak control in the period after complete OPV cessation and post-polio eradication.

The Production of a Stable Infliximab Powder: The Evaluation of Spray and Freeze-Drying for Production.

In prospect of developing an oral dosage form of Infliximab, for treatment of Crohn's disease and rheumatoid arthritis, freeze-drying (vial vs Lyoguard trays) and spray-drying were investigated as production method for stable powders. Dextran and inulin were used in combination with sucrose as stabilizing excipients. The drying processes did not affect Infliximab in these formulations, i.e. both the physical integrity and biological activity (TNF binding) were retained. Accelerated stability studies (1 month at 60°C) showed that the TNF binding ability of Infliximab was conserved in the freeze-dried formulations, whereas the liquid counterpart lost all TNF binding. After thermal treatment, the dried formulations showed some chemical modification of the IgG in the dextran-sucrose formulation, probably due to Maillard reaction products. This study indicates that, with the appropriate formulation, both spray-drying and freeze-drying may be useful for (bulk) powder production of Infliximab.

A Design of Experiment approach to predict product and process parameters for a spray dried influenza vaccine.

Spray dried vaccine formulations might be an alternative to traditional lyophilized vaccines. Compared to lyophilization, spray drying is a fast and cheap process extensively used for drying biologicals. The current study provides an approach that utilizes Design of Experiments for spray drying process to stabilize whole inactivated influenza virus (WIV) vaccine. The approach included systematically screening and optimizing the spray drying process variables, determining the desired process parameters and predicting product quality parameters. The process parameters inlet air temperature, nozzle gas flow rate and feed flow rate and their effect on WIV vaccine powder characteristics such as particle size, residual moisture content (RMC) and powder yield were investigated. Vaccine powders with a broad range of physical characteristics (RMC 1.2-4.9%, particle size 2.4-8.5µm and powder yield 42-82%) were obtained. WIV showed no significant loss in antigenicity as revealed by hemagglutination test. Furthermore, descriptive models generated by DoE software could be used to determine and select (set) spray drying process parameter. This was used to generate a dried WIV powder with predefined (predicted) characteristics. Moreover, the spray dried vaccine powders retained their antigenic stability even after storage for 3 months at 60°C. The approach used here enabled the generation of a thermostable, antigenic WIV vaccine powder with desired physical characteristics that could be potentially used for pulmonary administration.

Incompatibility of lyophilized inactivated polio vaccine with liquid pentavalent whole-cell-pertussis-containing vaccine.

A hexavalent vaccine containing diphtheria toxoid, tetanus toxoid, whole cell pertussis, Haemophilius influenza type B, hepatitis B and inactivated polio vaccine (IPV) may: (i) increase the efficiency of vaccination campaigns, (ii) reduce the number of injections thereby reducing needlestick injuries, and (iii) ensure better protection against pertussis as compared to vaccines containing acellular pertussis antigens. An approach to obtain a hexavalent vaccine might be reconstituting lyophilized polio vaccine (IPV-LYO) with liquid pentavalent vaccine just before intramuscular delivery. The potential limitations of this approach were investigated including thermostability of IPV as measured by D-antigen ELISA and rat potency, the compatibility of fluid and lyophilized IPV in combination with thimerosal and thimerosal containing hexavalent vaccine. The rat potency of polio type 3 in IPV-LYO was 2 to 3-fold lower than standardized on the D-antigen content, suggesting an alteration of the polio type 3 D-antigen particle by lyophilization. Type 1 and 2 had unaffected antigenicity/immunogenicity ratios. Alteration of type 3 D-antigen could be detected by showing reduced thermostability at 45°C compared to type 3 in non-lyophilized liquid controls. Reconstituting IPV-LYO in the presence of thimerosal (TM) resulted in a fast temperature dependent loss of polio type 1-3 D-antigen. The presence of 0.005% TM reduced the D-antigen content by ∼20% (polio type 2/3) and ∼60% (polio type 1) in 6h at 25°C, which are WHO open vial policy conditions. At 37°C, D-antigen was diminished even faster, suggesting that very fast, i.e., immediately after preparation, intramuscular delivery of the conceived hexavalent vaccine would not be a feasible option. Use of the TM-scavenger, l-cysteine, to bind TM (or mercury containing TM degradation products), resulted in a hexavalent vaccine mixture in which polio D-antigen was more stable.

Influenza Vaccine Manufacturing: Effect of Inactivation, Splitting and Site of Manufacturing. Comparison of Influenza Vaccine Production Processes.

The aim of this study was to evaluate the impact of different inactivation and splitting procedures on influenza vaccine product composition, stability and recovery to support transfer of process technology. Four split and two whole inactivated virus (WIV) influenza vaccine bulks were produced and compared with respect to release criteria, stability of the bulk and haemagglutinin recovery. One clarified harvest of influenza H3N2 A/Uruguay virus prepared on 25.000 fertilized eggs was divided equally over six downstream processes. The main unit operation for purification was sucrose gradient zonal ultracentrifugation. The inactivation of the virus was performed with either formaldehyde in phosphate buffer or with beta-propiolactone in citrate buffer. For splitting of the viral products in presence of Tween®, either Triton™ X-100 or di-ethyl-ether was used. Removal of ether was established by centrifugation and evaporation, whereas removal of Triton-X100 was performed by hydrophobic interaction chromatography. All products were sterile filtered and subjected to a 5 months real time stability study. In all processes, major product losses were measured after sterile filtration; with larger losses for split virus than for WIV. The beta-propiolactone inactivation on average resulted in higher recoveries compared to processes using formaldehyde inactivation. Especially ether split formaldehyde product showed low recovery and least stability over a period of five months.

Alternative administration routes and delivery technologies for polio vaccines.

Global polio eradication is closer than ever. Replacement of the live attenuated oral poliovirus vaccine (OPV) by inactivated poliovirus vaccine (IPV) is recommended to achieve complete eradication. Limited global production capacity and relatively high IPV costs compared to OPV spur the need for improved polio vaccines. The target product profile of these vaccines includes not only dose sparing but also high stability, which is important for stockpiling, and easy application important for (emergency) vaccination campaigns. In this review, the current status of alternative polio vaccine delivery strategies is given. Furthermore, we discuss the feasibility of these strategies by highlighting challenges, hurdles to overcome, and formulation issues relevant for optimal vaccine delivery.

Predicting the influence of liposomal lipid composition on liposome size, zeta potential and liposome-induced dendritic cell maturation using a design of experiments approach.

In this study, the effect of liposomal lipid composition on the physicochemical characteristics and adjuvanticity of liposomes was investigated. Using a design of experiments (DoE) approach, peptide-containing liposomes containing various lipids (EPC, DOPE, DOTAP and DC-Chol) and peptide concentrations were formulated. Liposome size and zeta potential were determined for each formulation. Moreover, the adjuvanticity of the liposomes was assessed in an in vitro dendritic cell (DC) model, by quantifying the expression of DC maturation markers CD40, CD80, CD83 and CD86. The acquired data of these liposome characteristics were successfully fitted with regression models, and response contour plots were generated for each response factor. These models were applied to predict a lipid composition that resulted in a liposome with a target zeta potential. Subsequently, the expression of the DC maturation factors for this lipid composition was predicted and tested in vitro; the acquired maturation responses corresponded well with the predicted ones. These results show that a DoE approach can be used to screen various lipids and lipid compositions, and to predict their impact on liposome size, charge and adjuvanticity. Using such an approach may accelerate the formulation development of liposomal vaccine adjuvants.

Development of cross-protective influenza a vaccines based on cellular responses.

Seasonal influenza vaccines provide protection against matching influenza A virus (IAV) strains mainly through the induction of neutralizing serum IgG antibodies. However, these antibodies fail to confer a protective effect against mismatched IAV. This lack of efficacy against heterologous influenza strains has spurred the vaccine development community to look for other influenza vaccine concepts, which have the ability to elicit cross-protective immune responses. One of the concepts that is currently been worked on is that of influenza vaccines inducing influenza-specific T cell responses. T cells are able to lyse infected host cells, thereby clearing the virus. More interestingly, these T cells can recognize highly conserved epitopes of internal influenza proteins, making cellular responses less vulnerable to antigenic variability. T cells are therefore cross-reactive against many influenza strains, and thus are a promising concept for future influenza vaccines. Despite their potential, there are currently no T cell-based IAV vaccines on the market. Selection of the proper antigen, appropriate vaccine formulation and evaluation of the efficacy of T cell vaccines remains challenging, both in preclinical and clinical settings. In this review, we will discuss the current developments in influenza T cell vaccines, focusing on existing protein-based and novel peptide-based vaccine formulations. Furthermore, we will discuss the feasibility of influenza T cell vaccines and their possible use in the future.