Exponential growth, high prevalence of SARS-CoV-2, and vaccine effectiveness associated with the Delta variant

Paul Elliott*, David Haw, Haowei Wang, Oliver Eales, Caroline E. Walters, Kylie E. C. Ainslie, Christina Atchison, Claudio Fronterre, Peter J. Diggle, Andrew J Page, Alexander J. Trotter, Sophie J. Prosolek, The COVID-19 Genomics UK (COG-UK) Consortium, Deborah Ashby, Christl A. Donnelly, Wendy Barclay, Graham Taylor, Graham Cooke, Helen Ward, Ara DarziSteven Riley*, Samuel C Robson, Nicholas J. Loman, Thomas R. Connor, Tanya Golubchik, Rocio T Martinez Nunez, Catherine Ludden, Sally Corden, Ian Johnston, David Bonsall, Colin P. Smith, Giselda Bucca, M Estee Torok, Kordo Saeed, Jacqui A Prieto, David K Jackson, William L Hamilton, Luke B Snell, Catherine Moore, Ewan M. Harrison, Rachel J Williams, Hannah Jones, John A Hartley, Chris Williams, Darren L Smith, Matthew Bashton, Andrew Nelson, Gregory R Young, Clare M McCann, Wen C Yew

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)
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SARS-CoV-2 infections were rising during early summer 2021 in many countries associated with the Delta variant. We assessed RT-PCR swab-positivity in the REal-time Assessment of Community Transmission-1 (REACT-1) study in England. We observed sustained exponential growth with average doubling time (June-July 2021) of 25 days driven by complete replacement of Alpha variant by Delta, and by high prevalence at younger less-vaccinated ages. Unvaccinated people were three times more likely than double-vaccinated people to test positive. However, after adjusting for age and other variables, vaccine effectiveness for double-vaccinated people was estimated at between ~50% and ~60% during this period in England. Increased social mixing in the presence of Delta had the potential to generate sustained growth in infections, even at high levels of vaccination.
Original languageEnglish
Article numberabl9551
Number of pages15
Issue number6574
Early online date2 Nov 2021
Publication statusPublished - 17 Dec 2021


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