Sequential delivery of LAIV and SARS-CoV-2 in the ferret model can reduce SARS-CoV-2 shedding and does not result in enhanced lung pathology

Co-circulation of SARS-CoV-2 and influenza viruses could pose unpredictable risks to health systems globally, with recent studies suggesting more severe disease outcomes in co-infected patients. The lack of a readily available COVID-19 vaccine has reinforced the importance of influenza vaccine programmes during the COVID-19 pandemic. Live Attenuated Influenza Vaccine (LAIV) is an important tool in protecting against influenza, particularly in children. However, it is unknown whether LAIV administration might influence the outcomes of acute SARS-CoV-2 infection or disease. To investigate this, quadrivalent LAIV (QLAIV) was administered to ferrets 3 days pre- or post-SARS-CoV-2 infection. LAIV administration did not exacerbate SARS-CoV-2 disease course or lung pathology with either regimen. Additionally, LAIV administered prior to SARS-CoV-2 infection significantly reduced SARS-CoV-2 replication and shedding in the upper respiratory tract (URT). We conclude that LAIV administration in close proximity to SARS-CoV-2 infection does not exacerbate mild disease and can reduce SARS-CoV-2 shedding. ### Competing Interest Statement At the time of data generation for this publication, Katarzyna E. Schewe, Jonathan Crowe and Oliver Dibben were employees and shareholders of AstraZeneca plc. AstraZeneca plc are the manufacturers of Fluenz Tetra/FluMist Quadrivalent intranasal influenza live virus vaccine.