Co-circulation of influenza A virus strains and emergence of pandemic via reassortment: The role of cross-immunity

► A SIRS model of two strains is assumed where co-infection is included. ► We model the impact of co-infection and cross-immunity on invasion and coexistence. ► We examine the probability that reassortant strains generated from mixed infection develop into pandemic. ► We find that the probability of pandemic emergence is greatly suppressed by cross-immunity.