Innovations for Clinical Development of a Broadly Protective Nasal Spray Flu Vaccine to be Presented by Vivaldi Biosciences at ISRV Options XIII Conference

Novel Influenza Challenge Virus Developed for DeltaFLU Phase 2 Clinical Trial

FORT COLLINS, Colorado and VIENNA, Austria – August 25, 2026 – Vivaldi Biosciences Inc., a clinical-stage biotechnology company developing nasal spray vaccines for viral respiratory diseases, will present innovative work supporting clinical development of its DeltaFLU influenza vaccine candidate at the International Society for Respiratory Viruses (ISRV) Options XIII Conference for the Control of Influenza in Washington, DC on August 30, 31 and September 1. DeltaFLU is designed to elicit broad protection against influenza viruses, including seasonal influenza strains and variants, and emerging strains with pandemic potential.

DeltaFLU is a nasal spray influenza vaccine candidate with an innovative mode of action. Intranasal immunization with DeltaFLU rapidly induces a broad immune response in the nasal passages, the

primary point of entry of influenza viruses. In preclinical studies, this mucosal immunity protected ferrets against a wide range of influenza virus strains and blocked virus transmission. DeltaFLU also generates broadly cross-neutralizing systemic antibodies and T cells. In the ferret model, the vaccine candidate elicited broad cross-protection and rapid responses to re-infection.

Vivaldi plans to evaluate DeltaFLU in two clinical trials in 2027, including a Phase 2 study in a controlled human infection model (CHIM) to test protection against a widely unmatched influenza challenge strain. The clinical program and development of the novel challenge strain for the CHIM are funded by the European Union's Horizon Europe Research & Innovation program, under grant agreement No. 101080692 with the FLUniversal consortium, of which Vivaldi is a member. Vivaldi previously has evaluated DeltaFLU component vaccine strains in four Phase 1 and 2 clinical trials.

At the ISRV Options XIII Conference for the Control of Influenza, members of Vivaldi’s influenza vaccine development team will present the following posters:

“Development of a H1N1 pdm09 influenza strain for use in a CHIM study to evaluate an intranasal broadly protective influenza vaccine,” Amy Aspelund, Vice President of Research & Development: Selection, evaluation and development of a novel influenza H1N1 challenge strain for GMP production and use in human dose optimization studies and a Phase 2 CHIM study.

“Identification of mutations affecting rescue and growth of wild-type pdm09 H1N1 influenza A strains in Vero and MDCK cells,” Alaura Hoag, Scientist: Analysis of mutation-based impacts on the rescue and

growth capabilities of pdm09 H1N1 influenza A strains in Vero and MDCK cell lines.

“Development of a fluorescent microneutralization assay (fMNA) on Vero cells for analysis of preclinical sera neutralizing capacity,” Charlotte Anderson, Associate Scientist: Development of a rapid and reliable assay to measure neutralizing antibodies in serum samples from ferrets immunized with DeltaFLU in preclinical studies.

DeltaFLU is composed of genetically modified, replication-deficient influenza vaccine strains that lack the gene for nonstructural protein 1 (NS1). Deletion of NS1 (DelNS1) results in the ability of DeltaFLU to

rapidly induce interferon, a signaling protein produced by the body to activate the immune response. DeltaFLU uses the unique immune-stimulating properties of DelNS1 vaccine strains in a prime-boost

immunization regimen that directs the immune response to conserved regions of the stem portion of hemagglutinin (HA), a glycoprotein on the influenza viral envelope. The specific combination of DelNS1

strains in the two-component DeltaFLU vaccine candidate directs antibodies to the HA stems of a broad range of influenza type A and B viruses. DeltaFLU is thus being developed to elicit an extraordinarily

broad response against multiple influenza virus subtypes and variants that cause disease in humans.

About Vivaldi Biosciences

Vivaldi is developing intranasal vaccines intended to elicit superior protection against influenza and other respiratory diseases, based on its DelNS1 technology platform. The company’s clinical-stage

vaccine candidates are DeltaFLU, intended for broad protection against influenza A and B strains, and DelNS1 H5N1, a Phase 2-ready vaccine candidate intended to elicit broad protection against highly pathogenic influenza strains with pandemic potential. The company’s Delta-19 combination vaccine candidate for Covid-19 and influenza is in preclinical development. Vivaldi’s Vero cell-based vaccine manufacturing system uses patented advances in production and purification for high yields and excellent purity. Vivaldi is a venture-backed company with operations at the Research Innovation Center at Colorado State University, Fort Collins, Colorado, and in Vienna, Austria. NGN Capital LLC is the company’s lead investor. Learn more at www.vivaldibiosciences.com. Connect with Vivaldi Biosciences on Linkedin and Twitter.

Contact

Doug Given, MD, PhD, MBA

CEO, Vivaldi Biosciences

Tel: +1 415 200 7785

info@vivaldibiosciences.com

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