4. Discussion
The COVID-19 pandemic caused by SARS-CoV-2 and its variants continues to pose a threat to human health globally. Although vaccination brought the pandemic under control to some extent, the large number of breakthrough infection cases may require annual COVID-19 vaccination. IAV is a common respiratory infectious virus that causes severe respiratory illnesses worldwide. WHO updates vaccines to prevent seasonal influenza epidemics every year. It was reported that the coinfection rate of SARS-CoV-2 and IAV during the COVID-19 pandemic was as high asĀ 49.8%.21 To date, no clinically effective prophylactics are available for the prevention of both SARS-CoV-2 and IAV infections, highlighting a need for the development of combined vaccines. The production of a combined influenza/SARS-CoV-2 Omicron vaccine capable of protecting from both IAV- and SARS-CoV-2-induced disease may reduce the cost, inconvenience, and administration burden of multiple independent vaccines. In our study, the immunogenicity and protective effect of the influenza/SARS-CoV-2 Omicron subunit combined vaccine adjuvanted with MF59 were evaluated in BALB/c mice. Data showed that the combined vaccine induced high levels of IgG, IgG1, and IgG2a antibodies, as well as influenza A H1N1/California/2009 virus-specific hemagglutination-inhibiting antibodies in BALB/c mice. Furthermore, the subunit combined vaccine induced high titers of neutralizing antibodies against SARS-CoV-2 Omicron BA.5 pseudovirus infection and effectively reduced the viral load of authentic SARS-CoV-2 Omicron BA.5.2 variant in the cell culture supernatants.
In conclusion, our study educed evidence showing the influenza/SARS-CoV-2 Omicron subunit combined vaccine to be a potential interventional candidate against COVID-19 and pandemic influenza coinfection, thus deserving of further translational development.
Author Contributions: N.Z., H.H., S.J., and J.Z. conceived the idea and designed the experiments. Z.Y., C.L., J.Z., W.X., L.X., Y.C., R.Y. and J.D. performed the experiments. N.Z. and Z.Y. analyzed the data. N.Z. wrote the draft, and J.Z., S.J. and H.H. revised the manuscript. All authors have read and agreed to the published version of the manuscript.
Funding: This work was supported by the Scientific Research Foundation (grant No. J-202106) and Innovation Training Program (grant No. X202301126) of Hangzhou City University to N.Z.
Conflicts of Interest: The authors declare no conflict of interest.