Beyond strain-specific immunity: Conserved antigenic targets, emerging platforms, and translational challenges in...

The global burden of respiratory viral disease is shaped by two enduring threats: influenza, responsible for 290,000-650,000 annual deaths, and coronaviruses, exemplified by the catastrophic SARS-CoV-2 pandemic that caused over 7 million confirmed fatalities and profound socioeconomic disruption. Current strain-specific vaccines remain inherently reactive, incapable of anticipating antigenic drift, reassortment, or zoonotic emergence. A paradigm shift toward universal vaccines-designed to target evolutionarily conserved viral epitopes and confer durable, broad-spectrum protection across strains, subtypes, and viral genera-represents the most strategically consequential frontier in contemporary vaccinology and pandemic preparedness.

This comparative narrative review provides an integrated synthesis of universal influenza vaccine (UIV) and pan-coronavirus vaccine (UCV) development, critically evaluating conserved immunological targets, advanced platform technologies, Phase I-III clinical pipeline status, and key translational barriers. By juxtaposing both developmental trajectories in a single analytical framework, we identify convergent scientific principles and divergent challenges to inform a unified pandemic preparedness strategy-an approach not previously addressed in the literature.

A structured narrative review was conducted via systematic literature search of PubMed, EMBASE, and ClinicalTrials.gov covering 2015-June 2026, supplemented by hand-searching reference lists of landmark studies. MeSH and free-text terms encompassed universal influenza vaccines, pan-coronavirus vaccines, mRNA vaccine platforms, hemagglutinin stalk, neuraminidase, M2e, receptor-binding domain (RBD), fusion peptide, S2 subunit, and broadly neutralizing antibodies. Peer-reviewed original research articles, Phase I-III clinical trial reports, and authoritative reviews were included; non-English publications and preclinical-only studies lacking translational immunogenicity data were excluded.

Conserved viral epitopes-principally the hemagglutinin (HA) stalk domain, neuraminidase (NA) ectodomain, and M2e protein for influenza, and the receptor-binding domain (RBD) Class 4 epitope, fusion peptide, and S2 subunit for coronaviruses-have been validated as targets for broadly neutralizing antibodies (bnAbs). Multiple advanced platforms, including lipid nanoparticle-encapsulated mRNA, adenoviral vectors, computationally designed self-assembling nanoparticles (Mosaic-8 RBD-I53-50, SpFN), and structure-guided protein antigens, are progressing through early-phase clinical trials with promising cross-reactive immunogenicity profiles. Comparative analysis reveals that UIV development benefits from well-characterised bnAb epitopes and established animal challenge models, while UCV development is accelerated by unprecedented mRNA manufacturing infrastructure and genomic surveillance networks built during the COVID-19 response. Shared translational obstacles include antigenic imprinting, the absence of validated correlates of protection for cross-strain immunity, and inequitable manufacturing scalability.

Cross-strain protective vaccines against influenza and coronaviruses are scientifically achievable, supported by converging immunological principles and advancing clinical evidence across both fields. Accelerating translation to population-level protection requires coordinated investment in epitope-focused antigen engineering, correlate-of-protection validation, adaptive regulatory frameworks, and equitable global manufacturing capacity. Crucially, the scientific and policy lessons of COVID-19-both the remarkable speed enabled by prior platform investments and the inequities exposed in global vaccine distribution-must be integrated into universal respiratory virus vaccine programmes now, before the next pandemic forces another reactive response.