Is Co-Infection with Influenza Virus a Protective Factor of COVID-19?

Background: An emerging outbreak of COVID-19 has rapidly caused global pandemic. Few studies were reported on the incidence and role of influenza virus co-infection on COVID-19.Methods: 273 hospitalized patients with COVID-19 and tests of influenza A/B virus were enrolled from February to March 2020 in Wuhan, China. Data on baseline characteristics, clinical manifestations and outcomes, laboratory findings were collected and analysed.Findings: The incidence of influenza virus co-infection in patients with COVID-19 was 55·3% (151/273), with 48·5% (133/273) of influenza A and 6·6% (18/273) of influenza B, respectively. Influenza virus co-infection was significantly more common in non-critical group (60·5%, 115/190) than critical group (43·4%, 36/83; p=0·01). The fatality of COVID-19 in influenza group was 9·9% (15/151), while it was 23·8% (29/122) in non-influenza group (p=0·01). Accordingly, the incidence of critical type was higher in influenza group (p=0·01). Cox regression analysis revealed that co-infection with influenza virus had significant reduction of fatality than non-influenza group (OR 0·470, p<0·05). Other fatality indicators included age (p=0·02), sex (OR 3·626, p=0·00), and low lymphocytes (OR 2·368, p=0·04).Interpretation: There is a high incidence of influenza virus co-infection in patients with COVID-19 in Wuhan, China. It seems like co-infection with influenza virus acts as a protective factor for COVID-19. The relationship between SARS-nCoV-2 and influenza virus co-infection warrants further studies.Funding Statement: This study was supported by National Natural Science Foundation of China Grant (No. 81800493).Declaration of Interests: All authors have no conflicts of interest to declare.Ethics Approval Statement: The procedure was approved by the Institutional Ethics Board of Tongji Medical College. The follow-up was up to March 22, 2020.