# The nanoemulsion adjuvant provides antigen dose-sparing effects and enhances maternal passive immune protection for the cell-cultured quadrivalent influenza virus subunit vaccine

## TL;DR

A nanoemulsion adjuvant boosts vaccine effectiveness and maternal protection against influenza in mice.

## Contribution

The nanoemulsion adjuvant enables a 125-fold antigen dose reduction while maintaining immunity and provides maternal-offspring protection.

## Key findings

- NE adjuvant induces strong anti-HA IgG and hemagglutination inhibition titers with reduced antigen dose.
- Maternal antibodies from NE-vaccinated mothers fully protect offspring against influenza virus challenge.
- NE enhances IFN-γ and CD8+ T-cell responses, improving both humoral and cellular immunity.

## Abstract

To elicit a robust immune response, an adjuvant can be combined with the antigen in influenza vaccine formulations. In this study, we evaluated the dose-sparing effect and safety of a squalene-based oil-in-water nanoemulsion (NE) adjuvant formulated with a cell culture-derived quadrivalent influenza vaccine. Immune responses-including anti-HA IgG antibody levels and hemagglutination inhibition (HAI) titers-were assessed, along with protection against a homologous challenge with influenza B virus (strain B/Maryland/15/2016 B/Victoria). We also investigated the influence of antigen dose on vaccine-induced immunity and the passive protection conferred to offspring via maternal antibody transfer. The NE adjuvant elicited strong anti-HA antibody responses in young adult mice, and these antibodies were effectively transferred from immunized mothers to their offspring. Furthermore, offspring born to NE-immunized mothers were protected against influenza virus challenge. Collectively, our results indicate that the NE formulation induces potent influenza-specific immune responses with dose-sparing effects and enables maternal transfer of protective immunity. These findings support the potential of NE as an effective adjuvant for MDCK cell-based influenza subunit vaccines. Importance. This study demonstrates that a squalene-based nanoemulsion (NE) adjuvant significantly enhances the immunogenicity and dose-sparing capacity of cell culture-derived quadrivalent influenza vaccines. Key advances include: (1) NE-adjuvanted vaccines achieved a remarkable 125-fold antigen dose reduction while maintaining antibody titers comparable to high-dose formulations, addressing critical challenges in pandemic preparedness; (2) NE induced robust humoral and cellular immunity, including elevated anti-HA IgG (10-fold increase vs. non-adjuvanted vaccine), improved HI titers, and enhanced IFN-γ/CD8 + T-cell responses; (3) Unique maternal-offspring protection was demonstrated, with transferred maternal antibodies conferring 100% survival in offspring against viral challenge. These findings position NE as an effective adjuvant technology that simultaneously optimizes antigen use and broadens immune protection across age groups.

The online version contains supplementary material available at 10.1186/s12985-025-03006-z.