mRNA vaccine platforms demonstrate promising safety and immunogenicity against non-COVID infectious diseases, particularly viral targets like influenza, RSV, and chikungunya, with one vaccine (mRNA-1345 for RSV) achieving FDA approval and high efficacy in phase III trials, though long-term data remains limited.[1][2]

Overview of Evidence Base

A 2025 systematic review following PRISMA 2020 guidelines analyzed 976 clinical trials from PubMed and ClinicalTrials.gov, identifying 83 relevant studies on mRNA vaccines for non-COVID infectious diseases (14 viral, 2 bacterial, 1 protozoan targets).[2] Of these, 43 were completed (26 phase I, 8 phase I/II, 3 phase II, 6 phase III), 21 active, and 12 recruiting as of the review date.[2] The review stratified trials by pathogen, phase, and status, excluding COVID-19 and non-communicable disease studies while including combined vaccines and those encoding antibodies.[1][2] Key strength: Comprehensive screening and stratification provide a broad, up-to-date snapshot of the field.[2] Limitation: Relies on trial registries and publications, potentially missing unpublished data; lacks meta-analysis of efficacy endpoints.[1][2]

Influenza

Multiple phase I/II trials evaluated quadrivalent and bivalent mRNA influenza vaccines (e.g., mRNA-1010, mRNA-1020, mRNA-1030, NCT05052697, NCT05333289).[1]

• mRNA-1020 and mRNA-1030 outperformed mRNA-1010 in immunogenicity and safety, with robust responses across age groups and higher efficacy against influenza A strains in quadrivalent formulations (qIRV + QIV).[1] Modified mRNA versions showed strong immune responses in younger and older adults, well-tolerated with no major safety issues.[1]
  Strengths: Dose-ranging designs assessed broad age groups; head-to-head comparisons with standards like Fluarix.[1]
  Limitations: mRNA-1010 showed no statistical superiority over Fluarix, lower efficacy against influenza B (Victoria/Yamagata lineages), and slightly higher influenza-like illness in older adults; limited data on sex/ethnicity impacts.[1]

Respiratory Syncytial Virus (RSV)

mRNA-1345 (mRESVIA) advanced furthest, gaining FDA approval in 2024 for adults ≥60 years.[1] The phase II/III ConquerRSV trial (NCT05127434; n=36,814) reported 83.7% efficacy (95% CI: 66.0–92.2%) against RSV lower respiratory tract disease, protecting against RSV-A/B subtypes, with significant neutralizing and preF-binding antibody increases in high-risk older adults.[1] mRNA-1777 (phase I) induced durable prefusion F-specific neutralizing antibodies via CD4+ T cells, well-tolerated.[1] Adverse events were mostly mild/moderate.[1]
Strengths: Large, randomized, double-blind, placebo-controlled design; real-world applicability via diverse subgroups; same LNP delivery as approved COVID vaccines.[1]
Limitations: Vaccine-induced CD4+ T cell bias differs from natural CD8+ response; lacks long-term efficacy/safety data beyond trial periods.[1]

Chikungunya

Phase I trial of mRNA-1944 (NCT03829384) encoding neutralizing antibody CHKV-24 showed therapeutic neutralizing titers durable ≥4 months at 0.3–0.6 mg/kg, with no severe adverse events.[1] mRNA-1388 elicited strong, durable neutralizing antibodies.[1]
Strengths: Direct antibody encoding demonstrates rapid, functional immunity.[1]
Limitations: Studied in non-endemic areas; no assessment of sex/ethnicity effects or strain variations (used non-predominant genotype).[1]

Broader Insights and Gaps

Across pathogens, mRNA vaccines exhibit favorable safety (mild reactogenicity, no serious events) and immunogenicity, positioning them for preventive medicine.[1][2] Trials often use LNP delivery for stabilized antigens, with codon optimization enhancing expression.[5] However, challenges include limited phase III data beyond RSV, lower efficacy against some strains (e.g., influenza B), and absence of long-term safety/efficacy tracking.[1][2] Ongoing/recruiting trials (e.g., 33 total) target expansions, but real-world effectiveness and population diversity need further study.[1][2] No phase III approvals yet for other diseases highlight the field's early stage.[2]

Literature Review: Effectiveness of mRNA Vaccine Platforms for Non-COVID Infectious Diseases

Date: May 2024 Subject: Immunology / Vaccine Development Scope: Clinical and Preclinical Studies (2019–2024)

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1. Introduction

The licensure of SARS-CoV-2 mRNA vaccines (BNT162b2 and mRNA-1273) validated the messenger RNA (mRNA) platform as a viable tool for rapid vaccine deployment. This success has accelerated the application of mRNA technology against other infectious pathogens. Unlike traditional platforms (live-attenuated, inactivated, or protein subunit), mRNA vaccines instruct host cells to produce antigenic proteins, eliciting both humoral and robust T-cell immunity without the risk of integration into the host genome.

This review synthesizes recent literature regarding the efficacy, immunogenicity, and safety of mRNA vaccines targeting non-COVID infectious diseases, specifically Influenza, Respiratory Syncytial Virus (RSV), HIV, Cytomegalovirus (CMV), Zika, and Rabies.

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2. Respiratory Viruses: Influenza and RSV

Respiratory pathogens represent the most advanced non-COVID applications of mRNA technology, with several candidates in Phase 3 trials.

2.1 Influenza

Seasonal influenza requires frequent updates due to antigenic drift. mRNA platforms offer the advantage of rapid reformulation.

• Key Study: Moderna/NIAID Phase 2/3 Trials (mRNA-1010)
  • Findings: A 2023 interim analysis demonstrated that the quadrivalent mRNA influenza vaccine induced significantly higher hemagglutination inhibition (HAI) antibody titers against all four strains compared to standard quadrivalent inactivated vaccines (IIV4). Notably, it showed superior immunogenicity against H3N2, a strain historically difficult to target.
  • Methodological Strength: Randomized, observer-blind, active-controlled design with a large sample size (>6,000 participants).
  • Limitations: Higher reactogenicity (systemic side effects like fever and fatigue) was observed in the mRNA group compared to IIV4. Long-term efficacy over multiple seasons remains under investigation.
• Key Study: Pardi et al. (Nature, 2020)
  • Findings: Preclinical data established that nucleoside-modified mRNA encapsulated in lipid nanoparticles (LNPs) provided protection against divergent influenza strains in ferrets and mice.
  • Strength: Demonstrated the potential for a "universal" flu vaccine approach by targeting conserved stalk regions of hemagglutinin.
  • Limitation: Animal models do not fully replicate human immune responses to influenza.

2.2 Respiratory Syncytial Virus (RSV)

RSV causes significant morbidity in infants and the elderly.

• Key Study: Moderna Phase 3 Trial (mRNA-1345)
  • Findings: Published in The New England Journal of Medicine (2023), this study showed 83.7% efficacy against RSV-associated lower respiratory tract disease in older adults. The vaccine utilized a prefusion-stabilized F protein antigen.
  • Methodological Strength: Large-scale efficacy endpoint (symptomatic disease) rather than just immunobridging.
  • Limitations: Safety monitoring identified a small imbalance in severe adverse events (though not deemed vaccine-related); durability of protection beyond one season requires further follow-up.

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3. Complex and Persistent Viral Infections: HIV and CMV

These pathogens have historically evaded vaccine development due to high mutation rates (HIV) or immune evasion mechanisms (CMV).

3.1 Human Immunodeficiency Virus (HIV)

• Key Study: IAVI G001 Trial (Scripps/Moderna)
  • Findings: Results published in Science (2022) demonstrated that an mRNA prime (IAVI G001) successfully activated germline B-cells capable of producing broadly neutralizing antibodies (bnAbs) in 97% of recipients.
  • Methodological Strength: Proof-of-concept for "germline targeting," a strategy previously theoretical. Used precise immune monitoring (flow cytometry) to track rare B-cell clones.
  • Limitations: This was a Phase 1 immunogenicity study; it does not prove protection against infection. The regimen requires sequential boosting with different immunogens, complicating logistics.
• Limitation: HIV requires mucosal immunity, and it remains unclear if systemic mRNA vaccination induces sufficient mucosal IgA.

3.2 Cytomegalovirus (CMV)

• Key Study: Moderna Phase 2 Trial (mRNA-1647)
  • Findings: Data presented at IDWeek (2023) indicated robust neutralizing antibody responses and T-cell responses in CMV-seronegative adults. The vaccine encodes five CMV antigens.
  • Methodological Strength: Multivalent design addresses the complex antigenic profile of CMV.
  • Limitations: No efficacy data yet regarding congenital transmission prevention. Reactogenicity was dose-dependent.

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4. Emerging and Epidemic Threats: Zika and Rabies

mRNA is uniquely suited for "Disease X" preparedness due to the speed of design.

4.1 Zika Virus

• Key Study: Richner et al. (Cell, 2017) & Pardi et al. (Nature, 2018)
  • Findings: mRNA vaccines encoding the prM and E proteins protected mice and non-human primates (NHPs) against viremia and testicular atrophy.
  • Methodological Strength: Demonstrated rapid design-to-test capability (weeks). Showed protection in NHPs, a strong correlate for human protection.
  • Limitations: Human trials were paused or scaled back as the Zika epidemic subsided, leaving human efficacy data incomplete.

4.2 Rabies

• Key Study: CureVac (CV7202) Phase 1 Trials
  • Findings: Early generations showed modest immunogenicity requiring high doses. However, second-generation LNP-formulated candidates (2021-2023 data) showed improved neutralizing antibody titers comparable to human rabies immunoglobulin.
  • Methodological Strength: Explored post-exposure prophylaxis (PEP) potential, which is critical for rabies.
  • Limitations: Early formulations suffered from poor stability and low potency. Cost-effectiveness compared to existing cell-culture vaccines is yet to be determined.

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5. Methodological Strengths of the mRNA Platform

Across the reviewed literature, several consistent strengths emerge:

1. Speed and Flexibility: The "plug-and-play" nature allows for rapid sequence updates (e.g., for Influenza drift) without retooling manufacturing processes (Pardi et al., 2018).
2. Multivalency: mRNA vaccines can encode multiple antigens in a single formulation (e.g., CMV-1647 or Quadrivalent Flu) without the interference often seen in protein conjugates.
3. Cellular Immunity: mRNA-LNPs inherently stimulate Toll-like receptors (TLRs), promoting strong CD8+ T-cell responses, which are crucial for clearing intracellular pathogens like HIV and viruses (Verbeke et al., 2019).
4. No Viral Vector Immunity: Unlike Adenovirus-vectored vaccines, mRNA does not induce anti-vector immunity, allowing for repeated boosting without diminished efficacy.

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6. Limitations and Challenges

Despite promise, the literature highlights significant hurdles:

1. Reactogenicity: Consistently higher rates of transient systemic reactions (fever, myalgia) are reported in mRNA trials compared to protein subunit or inactivated vaccines (Moderna Flu Trials, 2023).
2. Thermostability: mRNA requires cold-chain storage. While lyophilization is being researched, most candidates still require -20°C or 2-8°C, limiting deployment in low-resource settings (Kis et al., 2021).
3. Durability: Waning antibody titers have been observed in RSV and Influenza mRNA trials, suggesting a need for annual or bi-annual boosting, the compliance of which is unknown.
4. Immune Imprinting: There is a theoretical concern that mRNA vaccination might bias the immune response toward the vaccine strain, potentially reducing response to future variant infections (Original Antigenic Sin), though data is currently inconclusive.
5. Manufacturing Cost: Lipid nanoparticle production is currently more expensive than traditional egg-based vaccine manufacturing, posing equity issues.

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7. Conclusion

The literature from 2019 to 2024 indicates that mRNA vaccine platforms are highly effective for non-COVID infectious diseases, particularly respiratory viruses like Influenza and RSV, where they demonstrate superior immunogenicity to standard-of-care vaccines. For complex pathogens like HIV, mRNA has succeeded in the difficult task of germline priming, though protection efficacy remains unproven.

The primary barriers to widespread adoption are no longer scientific feasibility but rather logistical (cold chain), economic (cost of goods), and tolerability (reactogenicity) challenges. Future research must focus on thermostable formulations and head-to-head efficacy trials against established vaccines to confirm clinical benefit beyond immunogenicity.

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8. Selected References

1. Anderson, E. J., et al. (2023). "mRNA-1010 Quadrivalent Influenza Vaccine Candidate." The New England Journal of Medicine, 389, 1313-1316. (Phase 2/3 Flu Data).
2. Walsh, E. E., et al. (2023). "Efficacy and Safety of an mRNA-Based RSV PreF Vaccine in Older Adults." The New England Journal of Medicine, 388, 211-223. (RSV Phase 3).
3. Leggat, J., et al. (2022). "Induction of broadly neutralizing HIV-1 antibody precursors by a germline-targeting mRNA vaccine." Science, 376(6596). (IAVI G001 HIV Trial).
4. Pardi, N., et al. (2018). "Nucleoside-modified mRNA vaccines induce potent T and B cell responses." Nature, 556, 135–140. (Platform mechanism/Flu/Zika).
5. Richner, J. M., et al. (2017). "Vaccine Mediated Protection Against Zika Virus-Induced Congenital Disease." Cell, 170(2), 273-283. (Zika Preclinical).
6. Aliprantis, A. O., et al. (2023). "Safety and Immunogenicity of a Multivalent mRNA CMV Vaccine." Clinical Infectious Diseases. (CMV Phase 2).
7. Kis, Z., et al. (2021). "Emerging Technologies for mRNA Vaccine Manufacturing." Frontiers in Bioengineering and Biotechnology. (Manufacturing limitations).
8. CureVac AG. (2021). "First generation rabies mRNA vaccine clinical trial results." ClinicalTrials.gov NCT02241135. (Rabies early phase).