The impact of viral genotype on pathogenesis and disease severity: respiratory syncytial virus and human rhinoviruses.

•RSV and HRV cause LRI, are linked to asthma, and show strain-specific virulence.•RSV strain-specific mucus induction has been mapped to the viral fusion protein.•HRV species C is associated with asthma, and A and C cause more disease than B.•Viral strain-specific phenotypes can be used to dissect pathogenesis mechanisms.•Distinct RSV fusion proteins induce more or less neutrophils which regulate IL-13.