# Immunogenicity Evaluation of Combination Respiratory Syncytial Virus and Varicella–Zoster Virus mRNA Vaccines in C57BL/6J Mice

## TL;DR

This study shows that combining RSV and VZV mRNA vaccines in mice produces immune responses similar to individual vaccines, suggesting a potential for fewer injections.

## Contribution

The study demonstrates the feasibility of combining two mRNA vaccines into a single formulation without compromising immune responses.

## Key findings

- Combined RSV and VZV mRNA vaccines elicited comparable IgG and neutralization titers to individual vaccines.
- Cell-mediated immunity and CD4+ T-cell responses were similar in combined and single mRNA formulations.
- Lipid nanoparticles effectively encapsulated both mRNAs with uniform particle sizes.

## Abstract

Background: Respiratory syncytial virus (RSV) and varicella–zoster virus (VZV) pose significant risks to the elderly and individuals with compromised immune systems. In this study, we investigated whether combining RSV and VZV vaccines could reduce the number of vaccination injections, thereby minimizing discomfort for elderly individuals and reducing manufacturing costs. Methods: In this study, we developed two types of combined RSV and VZV mRNA vaccines. Using RSV and VZV mRNA vaccines administered alone as controls, we evaluated the immune response elicited by the combined mRNA vaccines in C57BL/6J mice. Results: The results demonstrated that RSV mRNA, VZV mRNA, and a mixture of both could be effectively encapsulated in lipid nanoparticles (LNPs) with uniform particle sizes. Compared to the administration of either the RSV or VZV mRNA vaccine alone, the delivery of two kinds of mRNA LNP combination formulation—whether directly mixed or encapsulated two mRNAs in the same LNP formulation—elicited comparable IgG titers, neutralization titers, cell-mediated immunity (CMI), and CD4+ T-cell responses. Conclusions: In conclusion, this study establishes the feasibility of combining RSV and VZV mRNA-LNP vaccines, laying a solid foundation for clinical trials of combined RSV and VZV vaccines.