Influenza A H1N1 mediated pre-existing immunity to SARS-CoV-2 predicts COVID-19 outbreak dynamics

Susceptibility to SARSCoV2 infections is highly variable, ranging from asymptomatic and mild infections in most, to deadly outcome in few. Here, we present evidence that antibodies induced by currently circulating influenza A H1N1 (flu) strains cross react with the most critical receptor binding motif of the SARSCoV2 spike protein that interacts with the ACE2 receptor. About 58 to 68% of blood donors in Stockholm had detectable antibodies to this cross-reactive peptide, NGVEGF, and seasonal flu vaccination trended to enhance binding of inhibitory antibodies to SARSCoV2. This peptide also activated CD8 T cells in 20% of healthy subjects. Eleven additional CD8 T cell peptides that cross react with flu and SARSCoV2 were identified that potentially protect against SARSCoV2 in 40 to 71% of individuals, depending on their HLA type.