The roles of pre-season immunity, age, viral shedding, and community exposures in shaping influenza household transmission dynamics
- Molly K. Sauter
- Jackie Kleynhans
- Jocelyn Moyes
- Meredith L. McMorrow
- Florette K. Treurnicht
- Orienka Hellferscee
- Anne von Gottberg
- Nicole Wolter
- Amelia Buys
- Lorens Maake
- Neil A. Martinson
- Kathleen Kahn
- Limakatso Lebina
- Katlego Motlhaoleng
- Floidy Wafawanaka
- Francesc Xavier Gómez-Olivé
- Stefano Tempia
- Bryan Grenfell
- Cécile Viboud
- Kaiyuan Sun
- Cheryl Cohen
2026-07-30
Protective immunity against influenza transmission remains poorly understood due to the high prevalence of undetected asymptomatic infections. To address this, we analyze 1518 individuals and 623 infection episodes from a three-year, rural and urban, South African household cohort study that combines pre-season serum collection with twice-weekly virological testing regardless of symptoms. By developing a subtype/lineage-specific household transmission model and incorporating time-resolved viral shedding kinetics for all observed infections, we disentangle household and community exposure, pre-season immunity, and age effects. After adjusting for exposure intensity, pre-season hemagglutination inhibition (HAI) titers ≥1:40 are associated with a reduced infection risk for A(H1N1)pdm09, A(H3N2), and B/Victoria, but not B/Yamagata. However, children exhibit higher susceptibility and longer viral shedding durations than adults across all subtypes/lineages, even after accounting for pre-season HAI titers. Here, we show persistent age-related effects on influenza susceptibility and viral shedding, underscoring the need to explore immune mechanisms beyond HAI-based correlates of protection.