Reconstruction of SARS-CoV-2 transmissibility within households in the UK Virus Watch Study

Households provide ideal settings to study SARS-CoV-2 transmission due to close proximity and extended exposure among members. Understanding transmission patterns is crucial for implementing effective control measures. We analysed whole genome sequences from 237 subjects across 162 households within the Virus Watch Prospective Community Cohort Study (372 total participants). We incorporated minority variants as indicators of within-host genomic diversity into phylogenetic models to reconstruct viral relationships more accurately than using consensus sequences alone. In 73/162 households with multiple infections, phylogeny identified eight secondary cases resulting from separate introduction events rather than within-household transmission. For the remaining 65 households, including minority variants resolved transmission chains that were otherwise uncertain. Our approach demonstrates that integrating within-host genetic diversity into phylogenetic models alongside epidemiological data provides a robust method to accurately identify household transmission events, assess infection risk factors, and improve secondary attack rate estimation, essential for understanding viral spread dynamics.