COVID-19 due to the B.1.617.2 (Delta) variant compared to B.1.1.7 (Alpha) variant of SARS-CoV-2: a prospective observational cohort study
Authors: Kläser Kerstin , Molteni Erika , Graham Mark , Canas Liane S. , Österdahl Marc F. , Antonelli Michela , Chen Liyuan , Deng Jie , Murray Benjamin , Kerfoot Eric , Wolf Jonathan , May Anna , Fox Ben , Capdevila Joan ,   The COVID-19 Genomics U. K. (COG-UK) Consortium, Aanensen David M. , Abudahab Khalil , Adams Helen , Adams Alexander , Afifi Safiah , Aggarwal Dinesh , Ahmad Shazaad S. Y. , Aigrain Louise , Alcolea-Medina Adela , Alikhan Nabil-Fareed , Allara Elias , Amato Roberto , Angyal Adrienn , Annett Tara , Aplin Stephen , Ariani Cristina V. , Asad Hibo , Ash Amy , Ashfield Paula , Ashford Fiona , Atkinson Laura , Attwood Stephen W. , Auckland Cressida , Aydin Alp , Baker David J. , Baker Paul , Balcazar Carlos E. , Ball Jonathan , Barrett Jeffrey C. , Barrow Magdalena , Barton Edward , Bashton Matthew , Bassett Andrew R. , Batra Rahul , Baxter Chris , Bayzid Nadua , Beaver Charlotte , Beckett Angela H. , Beckwith Shaun M. , Bedford Luke , Beer Robert , Beggs Andrew , Bellis Katherine L. , Berry Louise , Bertolusso Beatrice , Best Angus , Betteridge Emma , Bibby David , Bicknell Kelly , Binns Debbie , Birchley Alec , Bird Paul W. , Bishop Chloe , Blacow Rachel , Blakey Victoria , Blane Beth , Bolt Frances , Bonfield James , Bonner Stephen , Bonsall David , Boswell Tim , Bosworth Andrew , Bourgeois Yann , Boyd Olivia , Bradley Declan T. , Breen Cassie , Bresner Catherine , Breuer Judith , Bridgett Stephen , Bronner Iraad F. , Brooks Ellena , Broos Alice , Brown Julianne R. , Bucca Giselda , Buchan Sarah L. , Buck David , Bull Matthew , Burns Phillipa J. , Burton-Fanning Shirelle , Byaruhanga Timothy , Byott Matthew , Campbell Sharon , Carabelli Alessandro M. , Cargill James S. , Carlile Matthew , Carvalho Sílvia F. , Casey Anna , Castigador Anibolina , Catalan Jana , Chalker Vicki , Chaloner Nicola J. , Chand Meera , Chappell Joseph G. , Charalampous Themoula , Chatterton Wendy , Chaudhry Yasmin , Churcher Carol M. , Clark Gemma , Clarke Phillip , Cogger Benjamin J. , Cole Kevin , Collins Jennifer , Colquhoun Rachel , Connor Thomas R. , Cook Kate F. , Coombes Jason , Corden Sally , Cormie Claire , Cortes Nicholas , Cotic Marius , Cotton Seb , Cottrell Simon , Coupland Lindsay , Cox MacGregor , Cox Alison , Craine Noel , Crawford Liam , Cross Aidan , Crown Matthew R. , Crudgington Dorian , Cumley Nicola , Curran Tanya , Curran Martin D. , da Silva Filipe Ana , Dabrera Gavin , Darby Alistair C. , Davidson Rose K. , Davies Alisha , Davies Robert M. , Davis Thomas , de Angelis Daniela , De Lacy Elen , de Oliveira Martins Leonardo , de Silva Thushan I. , Debebe Johnny , Denton-Smith Rebecca , Dervisevic Samir , Dewar Rebecca , Dey Jayasree , Dias Joana , Dobie Donald , Dorman Matthew J. , Downing Fatima , Driscoll Megan , du Plessis Louis , Duckworth Nichola , Durham Jillian , Eastick Kirstine , Easton Lisa J. , Eccles Richard , Edgeworth Jonathan , Edwards Sue , Bouzidi Kate El , Eldirdiri Sahar , Ellaby Nicholas , Elliott Scott , Eltringham Gary , Ensell Leah , Erkiert Michelle J. , Zamudio Marina Escalera , Essex Sarah , Evans Johnathan M. , Evans Cariad , Everson William , Fairley Derek J. , Fallon Karlie , Fanaie Arezou , Farr Ben W. , Fearn Christopher , Feltwell Theresa , Ferguson Lynne , Fina Laia , Flaviani Flavia , Fleming Vicki M. , Forrest Sally , Foster-Nyarko Ebenezer , Foulkes Benjamin H. , Foulser Luke , Fragakis Mireille , Frampton Dan , Francois Sarah , Fraser Christophe , Freeman Timothy M. , Fryer Helen , Fuchs Marc , Fuller William , Gajee Kavitha , Galai Katerina , Gallagher Abbie , Gallagher Eileen , Gallagher Michael D. , Gallis Marta , Gaskin Amy , Gatica-Wilcox Bree , Geidelberg Lily , Gemmell Matthew , Georgana Iliana , George Ryan P. , Gifford Laura , Gilbert Lauren , Girgis Sophia T. , Glaysher Sharon , Goldstein Emily J. , Golubchik Tanya , Gomes Andrea N. , Gonçalves Sónia , Goodfellow Ian G. , Goodwin Scott , Goudarzi Salman , Gourtovaia Marina , Graham Clive , Graham Lee , Grant Paul R. , Green Luke R. , Green Angie , Greenaway Jane , Gregory Richard , Guest Martyn , Gunson Rory N. , Gupta Ravi K. , Gutierrez Bernardo , Haldenby Sam T. , Hamilton William L. , Hansford Samantha E. , Haque Tanzina , Harris Kathryn A. , Harrison Ian , Harrison Ewan M. , Hart Jennifer , Hartley John A. , Harvey William T. , Harvey Matthew , Hassan-Ibrahim Mohammed O. , Heaney Judith , Helmer Thomas , Henderson John H. , Hesketh Andrew R. , Hey Jessica , Heyburn David , Higginson Ellen E. , Hill Verity , Hill Jack D. , Hilson Rachel A. , Hilvers Ember , Holden Matthew T. G. , Hollis Amy , Holmes Christopher W. , Holmes Nadine , Holmes Alison H. , Hopes Richard , Hornsby Hailey R. , Hosmillo Myra , Houlihan Catherine , Howson-Wells Hannah C. , Hsu Sharon N. , Hubb Jonathan , Huckson Hannah , Hughes Warwick , Hughes Joseph , Hughes Margaret , Hutchings Stephanie , Idle Giles , Illingworth Chris J. , Impey Robert , Irish-Tavares Dianne , Iturriza-Gomara Miren , Izuagbe Rhys , Jackson Chris , Jackson Ben , Jackson Leigh M. , Jackson Kathryn A. , Jackson David K. , Jahun Aminu S. , James Victoria , James Keith , Jeanes Christopher , Jeffries Aaron R. , Jeremiah Sarah , Jermy Andrew , John Michaela , Johnson Rob , Johnson Kate , Johnston Ian , Jones Owen , Jones Sophie , Jones Hannah , Jones Christopher R. , Jones Neil , Joseph Amelia , Judges Sarah , Kay Gemma L. , Kay Sally , Keatley Jon-Paul , Keeley Alexander J. , Kenyon Anita , Kermack Leanne M. , Khakh Manjinder , Kidd Stephen P. , Kimuli Maimuna , Kirk Stuart , Kitchen Christine , Kitchman Katie , Knight Bridget A. , Koshy Cherian , Kraemer Moritz U. G. , Kumziene-Summerhayes Sara , Kwiatkowski Dominic , Lackenby Angie , Laing Kenneth G. , Lampejo Temi , Langford Cordelia F. , Lavin Deborah , Lawton Andrew I. , Lee Jack C. D. , Lee David , Lensing Stefanie V. , Leonard Steven , Levett Lisa J. , Le-Viet Thanh , Lewis Jonathan , Lewis Kevin , Liddle Jennifier , Liggett Steven , Lillie Patrick J. , Lindsey Benjamin B. , Lister Michelle M. , Livett Rich , Lo Stephanie , Loman Nicholas J. , Loose Matthew W. , Louka Stavroula F. , Loveson Katie F. , Lowdon Sarah , Lowe Hannah , Lowe Helen L. , Lucaci Anita O. , Ludden Catherine , Lynch Jessica , Lyons Ronan A. , Lythgoe Katrina , Machin Nicholas W. , MacIntyre-Cockett George , Mack Andrew , Macklin Ben , Maclean Alasdair , Macnaughton Emily , Madona Pinglawathee , Maes Mailis , Maftei Laurentiu , Mahanama Adhyana I. K. , Mahungu Tabitha W. , Mair Daniel , Maksimovic Joshua , Malone Cassandra S. , Maloney Daniel , Manesis Nikos , Manley Robin , Mantzouratou Anna , Marchbank Angela , Mariappan Arun , Martincorena Inigo , Nunez Rocio T. Martinez , Mather Alison E. , Maxwell Patrick , Mayhew Megan , Mbisa Tamyo , McCann Clare M. , McCarthy Shane A. , McCluggage Kathryn , McClure Patrick C. , McCrone J. T. , McHugh Martin P. , McKenna James P. , McKerr Caoimhe , McManus Georgina M. , McMurray Claire L. , McMurray Claire , McNally Alan , Meadows Lizzie , Medd Nathan , Megram Oliver , Menegazzo Mirko , Merrick Ian , Michell Stephen L. , Michelsen Michelle L. , Mirfenderesky Mariyam , Mirza Jeremy , Miskelly Julia , Moles-Garcia Emma , Moll Robin J. , Molnar Zoltan , Monahan Irene M. , Mondani Matteo , Mookerjee Siddharth , Moore Christopher , Moore Jonathan , Moore Nathan , Moore Catherine , Morcrette Helen , Morgan Sian , Morgan Mari , Mori Matilde , Morriss Arthur , Moses Samuel , Mower Craig , Muir Peter , Mukaddas Afrida , Munemo Florence , Munn Robert , Murray Abigail , Murray Leanne J. , Murray Darren R. , Mutingwende Manasa , Myers Richard , Nastouli Eleni , Nebbia Gaia , Nelson Andrew , Nelson Charlotte , Nicholls Sam , Nichols Jenna , Nicodemi Roberto , Nomikou Kyriaki , O’Grady Justin , O’Brien Sarah , Odedra Mina , Ohemeng-Kumi Natasha , Oliver Karen , Orton Richard J. , Osman Husam , O’Toole Áine , Pacchiarini Nicole , Padgett Debra , Page Andrew J. , Park Emily J. , Park Naomi R. , Parker Matthew D. , Parmar Surendra , Partridge David G. , Pascall David , Patel Amita , Patel Bindi , Paterson Steve , Payne Brendan A. I. , Peacock Sharon J. , Pearson Clare , Pelosi Emanuela , Percival Benita , Perkins Jon , Perry Malorie , Pinckert Malte L. , Platt Steven , Podplomyk Olga , Pohare Manoj , Pond Marcus , Pope Cassie F. , Poplawski Radoslaw , Powell Jessica , Poyner Jennifer , Prestwood Liam , Price Anna , Price James R. , Prieto Jacqui A. , Pritchard David T. , Prosolek Sophie J. , Pugh Georgia , Pusok Monika , Pybus Oliver G. , Pymont Hannah M. , Quail Michael A. , Quick Joshua , Radulescu Clara , Raghwani Jayna , Ragonnet-Cronin Manon , Rainbow Lucille , Rajan Diana , Rajatileka Shavanthi , Ramadan Newara A. , Rambaut Andrew , Ramble John , Randell Paul A. , Randell Paul , Ratcliffe Liz , Raviprakash Veena , Raza Mohammad , Redshaw Nicholas M. , Rey Sara , Reynolds Nicola , Richter Alex , Robertson David L. , Robinson Esther , Robson Samuel C. , Rogan Fiona , Rooke Stefan , Rowe Will , Roy Sunando , Rudder Steven , Ruis Chris , Rushton Steven , Ryan Felicity , Saeed Kordo , Samaraweera Buddhini , Sambles Christine M. , Sanderson Roy , Sanderson Theo , Sang Fei , Sass Thea , Scher Emily , Scott Garren , Scott Carol , Sehmi Jasveen , Shaaban Sharif , Shah Divya , Shaw Jessica , Shelest Ekaterina , Shepherd James G. , Sheridan Liz A. , Sheriff Nicola , Shirley Lesley , Sillitoe John , Silviera Siona , Simpson David A. , Singh Aditi , Singleton Dawn , Skvortsov Timofey , Sloan Tim J. , Sluga Graciela , Smith Ken , Smith Kim S. , Smith Perminder , Smith Darren L. , Smith Louise , Smith Colin P. , Smith Nikki , Smollett Katherine L. , Snell Luke B. , Somassa Thomas , Southgate Joel , Spellman Karla , Chapman Michael H. Spencer , Spurgin Lewis G. , Spyer Moira J. , Stanley Rachael , Stanley William , Stanton Thomas D. , Starinskij Igor , Stockton Joanne , Stonehouse Susanne , Storey Nathaniel , Studholme David J. , Sudhanva Malur , Swindells Emma , Taha Yusri , Tan Ngee Keong , Tang Julian W. , Tang Miao , Taylor Ben E. W. , Taylor Joshua F. , Taylor Sarah , Temperton Ben , Templeton Kate E. , Thomas Claire , Thomson Laura , Thomson Emma C. , Thornton Alicia , Thurston Scott A. J. , Todd John A. , Tomb Rachael , Tong Lily , Tonkin-Hill Gerry , Torok M. Estee , Tovar-Corona Jaime M. , Trebes Amy , Trotter Alexander J. , Tsatsani Ioulia , Turnbull Robyn , Turtle Lance , Twohig Katherine A. , Umpleby Helen , Underwood Anthony P. , Vamos Edith E. , Vasylyeva Tetyana I. , Vattipally Sreenu , Vernet Gabrielle , Vipond Barry B. , Volz Erik M. , Walsh Sarah , Wang Dennis , Warne Ben , Warwick-Dugdale Joanna , Wastnedge Elizabeth , Watkins Joanne , Watson Louisa K. , Waugh Sheila , Webster Hermione J. , Weldon Danni , Westwick Elaine , Whalley Thomas , Wheeler Helen , Whitehead Mark , Whiteley Max , Whitwham Andrew , Wierzbicki Claudia , Willford Nicholas J. , Williams Lesley-Anne , Williams Rebecca , Williams Cheryl , Williams Chris , Williams Charlotte A. , Williams Rachel J. , Williams Thomas , Williams Catryn , Williamson Kathleen A. , Wilson-Davies Eleri , Witele Eric , Withell Karen T. , Witney Adam A. , Wolverson Paige , Wong Nick , Workman Trudy , Wright Victoria , Wright Derek W. , Wyatt Tim , Wyllie Sarah , Xu-McCrae Li , Yavus Mehmet , Yaze Geraldine , Yeats Corin A. , Yebra Gonzalo , Yew Wen C. , Young Gregory R. , Young Jamie , Zarebski Alex E. , Zhang Peijun , Modat Marc , Hammers Alexander , Spector Tim D. , Steves Claire J. , Sudre Carole H. , Ourselin Sebastien , Duncan Emma L. 
Published: June 2022

The Delta (B.1.617.2) variant was the predominant UK circulating SARS-CoV-2 strain between May and December 2021. How Delta infection compares with previous variants is unknown. This prospective observational cohort study assessed symptomatic adults participating in the app-based COVID Symptom Study who tested positive for SARS-CoV-2 from May 26 to July 1, 2021 (Delta overwhelmingly the predominant circulating UK variant), compared (1:1, age- and sex-matched) with individuals presenting from December 28, 2020 to May 6, 2021 (Alpha (B.1.1.7) the predominant variant). We assessed illness (symptoms, duration, presentation to hospital) during Alpha- and Delta-predominant timeframes; and transmission, reinfection, and vaccine effectiveness during the Delta-predominant period. 3581 individuals (aged 18 to 100 years) from each timeframe were assessed. The seven most frequent symptoms were common to both variants. Within the first 28 days of illness, some symptoms were more common with Delta versus Alpha infection (including fever, sore throat, and headache) and some vice versa (dyspnoea). Symptom burden in the first week was higher with Delta versus Alpha infection; however, the odds of any given symptom lasting ≥ 7 days was either lower or unchanged. Illness duration ≥ 28 days was lower with Delta versus Alpha infection, though unchanged in unvaccinated individuals. Hospitalisation for COVID-19 was unchanged. The Delta variant appeared more (1.49) transmissible than Alpha. Re-infections were low in all UK regions. Vaccination markedly reduced the risk of Delta infection (by 69-84%). We conclude that COVID-19 from Delta or Alpha infections is similar. The Delta variant is more transmissible than Alpha; however, current vaccines showed good efficacy against disease. This research framework can be useful for future comparisons with new emerging variants.