Influenza-Infected Pigs Are Not Susceptible to SARS-CoV-2 Infection

Since its emergence in 2019, SARS-CoV-2 has resulted in more than 7.1 million deaths worldwide. It has been shown that co-infection with influenza A virus (IAV) can worsen clinical symptoms in COVID-19 patients and small animal models have been used to elucidate the molecular mechanisms of co-infection between SARS-CoV-2 and IAV. This study aimed to establish a co-infection model in pigs, a natural reservoir for IAV but resistant to SARS-CoV-2 infection, by determining whether pigs become susceptible to SARS-CoV-2 following a primary IAV infection. Here, pigs were primarily infected with swine influenza A virus (SIV) via the intratracheal route and, 3 days later, secondarily challenged with SARS-CoV-2. SIV was isolated from nasal swabs, and pigs seroconverted to SIV. In contrast, SARS-CoV-2 RNA was detected in nasal and oropharyngeal swabs only at day 1 post-secondary challenge, with no evidence of seroconversion against SARS-CoV-2. These data indicate that pigs are not susceptible to SARS-CoV-2 following SIV infection and therefore are not a suitable model for IAV/SARS-CoV-2 co-infection research.