SARS-CoV-2 and Influenza Virus Coinfections in the Tuscan Population during the 2021/2022 Influenza Season

The 2021/2022 influenza season was not characterised by a well-defined incidence peak. A high value of incidence was recorded in week 13, but it was still lower than in other influenza seasons. This abnormal circulation was probably due to relaxation of the COVID-19 pandemic restriction measures, which greatly reduced the circulation of respiratory-transmitted viruses, including human respiratory syncytial virus (HRSV). The symptoms of SARS-CoV-2 and influenza are quite similar, sharing the human-to-human transmission route via respiratory droplets. The aim of this study was to estimate the rate of coinfection with influenza viruses and/or HRSV in SARS-CoV-2-positive subjects (N=940) in a population of central Italy during the 2021/2022 season. A total of 54 cases of coinfection were detected during the study period, 51 cases (5.4%) of SARS-CoV-2 and influenza virus and three cases (0.3%) of SARS-CoV-2 and HRSV coinfection. These results highlight the importance of continuous monitoring of the circulation of influenza virus and other respiratory viruses in the context of the COVID-19 pandemic.