Human organoid systems reveal in vitro correlates of fitness for SARS-CoV-2 B.1.1.7

A new phase of the COVID-19 pandemic has started as SARS-CoV-2 variants with increased transmissibility are emerging globally, calling for the development of reliable platforms to rapidly phenotype viruses. Currently, no rapid phenotyping system exists that both accurately models human biology and can be standardized properly. Organoids accurately model viral target cells in vivo, can be established from many tissues, passaged indefinitely, biobanked and shared. We found that the British variant (clade B.1.1.7), compared to an ancestral 614G-containing clade B virus, produced higher levels of infectious virus late in infection and had a higher replicative fitness in human airway, alveolar and intestinal organoid models. Our findings unveil extended shedding as a correlate of fitness for SARS-CoV-2, possibly explaining the rapid emergence of SARS-CoV-2 B.1.1.7. Combined with genomic surveillance systems, virus phenotyping using standardized organoid models may be implemented into public health decision making.