{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T06:24:24Z","timestamp":1787293464263,"version":"build-2736575974"},"reference-count":58,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T00:00:00Z","timestamp":1787270400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:p>Seasonal influenza vaccines provide variable protection against antigenically drifted influenza A (H1N1 and H3N2) and influenza B viruses. Broadly protective approaches using computationally optimized broadly reactive antigens (COBRAs) can enhance immunity against diverse strains. Bis-(3\u2032,5\u2032)-cyclic dimeric adenosine monophosphate (c-di-AMP) is a mucosal adjuvant that boosts vaccine-induced immune responses. Here, we hypothesized that intranasal multivalent COBRA hemagglutinin (HA) and neuraminidase (NA) vaccination with c-di-AMP would induce broad humoral and cellular immunity in mice. Immunologically na\u00efve and pre-immune DBA\/2J mice were intranasally immunized with pentavalent vaccine formulations containing COBRA recombinant HA and NA or corresponding wild-type antigens. Formulations were administered at low or high antigen doses, with or without the mucosal adjuvant c-di-AMP. Humoral and cellular immune responses were evaluated, along with protection following influenza A (H1N1 and H3N2) and influenza B viral challenge. Pentavalent COBRA HA\/NA intranasal vaccination adjuvanted with c-di-AMP induced strong humoral and cellular immune responses in murine models. Vaccination induced robust, dose-dependent total IgG and hemagglutination inhibition (HAI) titers, along with high frequencies of antigen-specific antibody-secreting cells and interferon-\u03b3 (IFN-\u03b3)-producing cells in pre-immune mice. Na\u00efve mice were also seroprotected mainly against H1N1 at higher vaccine doses. Following lethal challenge with H1N1, H3N2, and influenza B viruses, vaccinated mice exhibited reduced weight loss, decreased lung viral titers, and enhanced survival, with the strongest protection observed in adjuvanted groups across both na\u00efve and pre-immune models. These findings highlight the value of combining broadly protective COBRA vaccine candidates with advanced mucosal adjuvants to enhance efficacy against antigenically drifted influenza virus strains.<\/jats:p>","DOI":"10.3389\/fimmu.2026.1876199","type":"journal-article","created":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T05:37:41Z","timestamp":1787290661000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Intranasal delivery of a COBRA-based protein vaccine adjuvanted with c-di-AMP enhances breadth of protective immune responses against seasonal influenza viruses"],"prefix":"10.3389","volume":"17","author":[{"given":"Camila C. 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