Increased transmissibility of SARS-CoV-2 lineage B.1.1.7 by age and viral load
Authors: Lyngse Frederik Plesner , Mølbak Kåre , Skov Robert Leo , Christiansen Lasse Engbo , Mortensen Laust Hvas , Albertsen Mads , Møller Camilla Holten , Krause Tyra Grove , Rasmussen Morten , Michaelsen Thomas Yssing , Voldstedlund Marianne , Fonager Jannik , Steenhard Nina ,   The Danish Covid-19 Genome Consortium,   AAU Coordination,   AAU Laboratory, Brandt Jakob , Knuttson Simon , Sørensen Emil A. , Jensen Thomas B. N. , Sørensen Trine , Petersen Celine , Chiche-Lapierre Clarisse , Hansen Frederik T. , Collados Emilio F. , Berg Amalie , Bielidt Susanne R. , Dall Sebastian M. , Dvarionaite Erika , Hansen Susan H. , Jørgensen Vibeke R. , Nicolajsen Trine B. , Saei Wagma , Østergaard Stine K. ,   AAU Bioinformatics, Michaelsen Thomas Y. , Le-Quy Vang , Sereika Mantas , Kirkegaard Rasmus H. , Andersen Kasper S. , Andersen Martin H. ,   AAU CLAUDIA/IT, Hansen Karsten K. , Boye Mads , Bach Mads P. , Dissing Peter , Drastrup-Fjordbak Anton , Collin Michael , Büttner Finn ,   AAU Legal and Admin, Andersen Susanne , Otte Lea Sass ,   AAU SUND, Bøgsted Martin , Brøndum Rasmus ,   AAU Computer Science, Hose Katja , Sagi Tomer , Pakanec Miroslav ,   Statens Serum Institut, Fomsgaard Anders , Karst Søren M. , Gunlan Vithiagaran , Bennedbæk Marc , Sieber Raphael , Ellegaard Kirsten , Ingham Anna C. , Johannesen Thor B. , Basterrechea Martin , Lilje Berit , Ng Kim L. , Edslev Sofie M. , Baig Sharmin , Stegger Marc , Matusevicius Povilas , Christoffersen Lars Bustamante , Tang Man-Hung Eric , Svarrer Christina Wiid , Al-Tamimi Nour Saad , Bækvad-Hansen Marie , Byberg-Grauholm Jonas , Christiansen Mette Theilgaard , Jørgensen Karen Mare , Larsen Nicolai Balle , Cohen Arieh ,   Aalborg University Hospital, Krarup Henrik , Fuglsang-Damgaard David , Mølvadgaard Mette , Nielsen Marc T. K. ,   Rigshospitalet, Schønning Kristian , Pedersen Martin S. , Marvig Rasmus L. , Kirkby Nikolai ,   Hvidovre Hospital, Schneider Uffe V. , Castruita Jose A. S. , Jacobsen Nana G. , Andersen Christian Ø. ,   Aarhus University Hospital, Christiansen Mette , Larsen Ole H. , Skipper Kristian A. , Vang Søren , Handberg Kurt J. , Kobel Carl M. , Andersen Camilla , Tarpgaard Irene H. , Ellermann-Eriksen Svend ,   Odense University Hospital, Skov Marianne , Sydenham Thomas V. ,   Herlev Hospital, Nielsen Lene , Nilsson Line L. , Friis Martin B. , Sundelin Thomas , Hansen Thomas A. ,   Sygehus Lillebælt, Jensen Anders , Marmolin Ea S. ,   Zealand University Hospital, Nielsen Xiaohui C. , Schouw Christian H. ,   Sydvestjysk Sygehus, Coia John E. , Andersen Dorte T. , Kirkeby Carsten Thure 
Published: December 2021

New lineages of SARS-CoV-2 are of potential concern due to higher transmissibility, risk of severe outcomes, and/or escape from neutralizing antibodies. Lineage B.1.1.7 (the Alpha variant) became dominant in early 2021, but the association between transmissibility and risk factors, such as age of primary case and viral load remains poorly understood. Here, we used comprehensive administrative data from Denmark, comprising the full population (January 11 to February 7, 2021), to estimate household transmissibility. This study included 5,241 households with primary cases; 808 were infected with lineage B.1.1.7 and 4,433 with other lineages. Here, we report an attack rate of 38% in households with a primary case infected with B.1.1.7 and 27% in households with other lineages. Primary cases infected with B.1.1.7 had an increased transmissibility of 1.5–1.7 times that of primary cases infected with other lineages. The increased transmissibility of B.1.1.7 was multiplicative across age and viral load.