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
Kerstin Kläser, Erika Molteni, Mark S. Graham, Liane S. Canas, Marc F. Österdahl, Michela Antonelli, Liyuan Chen, Jie Deng, Benjamin Murray, Eric Kerfoot, Jonathan Wolf, Anna May, Ben Fox, Joan Capdevila Pujol, David M. Aanensen, Khalil Abudahab, Helen Adams, Alexander Adams, Safiah Afifi, Dinesh Aggarwal, Shazaad S. Y. Ahmad, Louise Aigrain, Adela Alcolea-Medina, Nabil-Fareed Alikhan, Elias Allara, Roberto Amato, Adrienn Angyal, Tara Annett, Stephen Aplin, Cristina V. Ariani, Hibo Asad, Amy Ash, Paula Ashfield, Fiona Ashford, Laura Atkinson, Stephen W. Attwood, Cressida Auckland, Alp Aydin, David Baker, Paul Baker, Carlos E. Balcazar, Jonathan K. Ball, Jeffrey C. Barrett, Magdalena Barrow, Edward Barton, Matthew Bashton, Andrew R. Bassett, Rahul Batra, Chris Baxter, Nadua Bayzid, Charlotte Beaver, Angela H. Beckett, Shaun M. Beckwith, Luke Bedford, Robert Beer, Andrew D. Beggs, Katherine L. Bellis, Louise Berry, Beatrice Bertolusso, Angus Best, Emma Betteridge, David Bibby, Kelly Bicknell, Debbie Binns, Alec Birchley, Paul Bird, Chloe Bishop, Rachel Blacow, Victoria Blakey, Beth Blane, Frances Bolt, James Bonfield, Stephen Bonner, David Bonsall, Tim Boswell, Andrew Bosworth, Yann Bourgeois, Olivia Boyd, Declan Bradley, Cassie Breen, Catherine Bresner, Judith Breuer, Stephen Bridgett, Iraad F. Bronner, Ellena Brooks, Alice Broos, Julianne R. Brown, Giselda Bucca, Sarah L. Buchan, David Buck, Matthew Bull, Phillipa Burns, Shirelle Burton-Fanning, Timothy Byaruhanga, Matthew Byott, Sharon L. Campbell, Alessandro M. Carabelli, James S. Cargill, Matthew Carlile, Silvia Carvalho
Abstract
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.