# Novel Intranasal Replication-Deficient NS1ΔC Flu Vaccine Confers Protection from Divergent Influenza A and B Viruses in Mice

## TL;DR

A new intranasal flu vaccine based on modified NS1ΔC viruses protects mice from various influenza A and B strains.

## Contribution

A trivalent intranasal NS1ΔC vaccine formulation that provides cross-protection against multiple influenza subtypes.

## Key findings

- Intranasal NS1ΔC vaccination activated cross-specific T-cell responses and reduced lung inflammation and viral load.
- The trivalent Flu/NS1ΔC vaccine improved survival and reduced weight loss in mice challenged with diverse influenza viruses.
- The vaccine showed protection against both homologous and antigenically drifted influenza A and B viruses.

## Abstract

Background/Objectives: The current strategy for seasonal influenza prophylaxis relies on updating the vaccine components annually to account for the rapid antigenic drift of viruses and the low cross-protective efficacy of available vaccines. Mutant influenza viruses with truncated or deleted NS1 protein are known to stimulate cross-specific T-cell immune response and provide protection against heterosubtypic influenza A and B viruses. Methods: We generated NS1ΔC influenza A and B viruses with C-terminal NS1 deletions by reverse genetics. In a mouse model, we assessed the safety and immunogenicity of the B/Lee/NS1ΔC strain upon intranasal administration, as well as the mechanism of its cross-protective efficacy against sublethal B/Victoria and B/Yamagata challenges. We then investigated the potential of the intranasal Flu/NS1ΔC vaccine–a trivalent formulation of NS1ΔC A/H1N1, A/H3N2, and B influenza viruses–to protect mice from lethal influenza infection with homologous, heterologous, and antigenically drifted influenza A and B viruses. Results: Intranasal immunization with the B/Lee/NS1ΔC strain was safe in mice. It activated cross-specific T-cell responses in the lungs and protected animals against heterologous challenge by reducing viral load, inflammation, and lung pathology. Immunization with the trivalent Flu/NS1ΔC vaccine formulation improved survival and reduced weight loss and viral load upon challenge with A/H1N1pdm, A/H2N2, A/H5N1, and B/Victoria viruses. Conclusions: The trivalent intranasal Flu/NS1ΔC influenza vaccine is a promising tool to improve seasonal influenza protection and preparedness for an influenza pandemic.