Favorable safety and immunogenicity of a combined quadrivalent influenza and recombinant SARS-CoV-2 vaccine in Sprague-Dawley rats for both primary and booster immunization.

INTRODUCTION

The concurrent circulation of influenza viruses and SARS‑CoV‑2 continues to strain global public health systems. Vaccination remains the cornerstone of defense, and combined vaccines offer a strategic advantage by simplifying logistics, reducing costs, and improving coverage.

METHODS

In this set of studies, we evaluated the safety and immunogenicity of a novel combined quadrivalent influenza and recombinant COVID‑19 vaccine (developed by Anhui Zhifei Longcom Biopharmaceutical Co., Ltd.), known as the Flu‑CoV2 vaccine, in Sprague‑Dawley rats. Three independent studies were conducted in accordance with ICH S6(R1) guidelines for Preclinical Safety Evaluation of Biotechnology‑Derived Pharmaceuticals: primary immunization (Study 1) and booster immunization following a prior history of either influenza (Study 2) or COVID‑19 (Study 3) vaccination. Immunogenicity was determined by immunoglobulin G (IgG) antibody enzyme‑linked immunosorbent assay, plaque reduction neutralization tests for SARS‑CoV‑2, and hemagglutination inhibition assays for influenza viruses.

RESULTS

No severe, life‑threatening, or fatal adverse reactions occurred during any of the studies. Transient injection‑site nodules in adjuvanted groups resolved completely, and all transient post‑vaccination shifts in hematologic and biochemical parameters normalized by the end of the recovery period. As a primary regimen, the Flu‑CoV2 vaccine effectively induced strong IgG and neutralizing antibody responses against both influenza and SARS‑CoV‑2. Administered as a booster, it markedly augmented specific antibody levels in pre‑immune models, demonstrating its potential to broadly enhance recall immune responses.

CONCLUSIONS

These preclinical data demonstrate a favorable safety profile and potent immunogenicity, supporting the further development of the Flu‑CoV2 vaccine as a promising tool to address the dual threat of influenza and COVID‑19.