Transmission bottlenecks are defined by the number of unique virions or genotypes that establish an infection, and they restrict viral diversity that passes from one infected host to another. Previous work identified a tight transmission bottleneck for seasonal influenza A virus (IAV) based on analysis of 43 household pairs, largely from a single A(H3N2) predominant season. While many viral and host factors are known to influence IAV transmission in households, their impact on the transmission b