It Takes Two to Tango: SARS-CoV-2 and Influenza Co-Circulation and Co-Vaccination

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus are dangerous respiratory pathogens with high pandemic potential. Since 2021, these two viruses have been co-circulating, which implies additional risks of co-infection with both pathogens. According to clinical data, influenza and SARS-CoV-2 cause sim-ilar symptoms, and co-infection can increase disease severity and significantly enhance the risks of pneumonia and acute respiratory distress syndrome progressing with a poor outcome. Therefore, management of such patients requires special consideration. Prophylactic vaccination is widely recognized as the most effective way to prevent COVID-19 and influenza and to reduce the severity of these diseases. A range of influ-enza and COVID-19 vaccines built on different technological platforms is currently available on the market, with proven effectiveness, immunogenicity, and safety. Im-portantly, multiple countries have approved recommendations for simultaneous vac-cination against both viral pathogens. This approach is more convenient for patients and is associated with better response to treatment, while also improving vaccine cov-erage and compliance and offering significant resource savings for healthcare systems. This review analyzes recent data on the simultaneous circulation of influenza and SARS-CoV-2 viruses worldwide. We review epidemiological data and the pathogenetic mechanisms of co-infection with these two viruses. Next, we focus on current ap-proaches to simultaneous and combined vaccination against influenza and COVID-19. We outline the types of vaccines and summarize the available findings on the effec-tiveness and safety of co-vaccination.