Effect of Delta variant on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK

Koen B. Pouwels*, Emma Pritchard, Philippa C. Matthews, Nicole Stoesser, David W. Eyre, Karina Doris Vihta, Thomas House, Jodie Hay, John I. Bell, John N. Newton, Jeremy Farrar, Derrick Crook, Duncan Cook, Emma Rourke, Ruth Studley, Tim E.A. Peto, Ian Diamond, A. Sarah Walker

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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The effectiveness of the BNT162b2 and ChAdOx1 vaccines against new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections requires continuous re-evaluation, given the increasingly dominant B.1.617.2 (Delta) variant. In this study, we investigated the effectiveness of these vaccines in a large, community-based survey of randomly selected households across the United Kingdom. We found that the effectiveness of BNT162b2 and ChAdOx1 against infections (new polymerase chain reaction (PCR)-positive cases) with symptoms or high viral burden is reduced with the B.1.617.2 variant (absolute difference of 10–13% for BNT162b2 and 16% for ChAdOx1) compared to the B.1.1.7 (Alpha) variant. The effectiveness of two doses remains at least as great as protection afforded by prior natural infection. The dynamics of immunity after second doses differed significantly between BNT162b2 and ChAdOx1, with greater initial effectiveness against new PCR-positive cases but faster declines in protection against high viral burden and symptomatic infection with BNT162b2. There was no evidence that effectiveness varied by dosing interval, but protection was higher in vaccinated individuals after a prior infection and in younger adults. With B.1.617.2, infections occurring after two vaccinations had similar peak viral burden as those in unvaccinated individuals. SARS-CoV-2 vaccination still reduces new infections, but effectiveness and attenuation of peak viral burden are reduced with B.1.617.2.

Original languageEnglish
JournalNature Medicine
Publication statusAccepted/In press - 2021

Bibliographical note

Funding Information:
This study is funded by the Department of Health and Social Care, with in-kind support from the Welsh Government, the Department of Health on behalf of the Northern Ireland Government and the Scottish Government. E.P., K.B.P., A.S.W., T.E.A.P., N.S. and D.E. are supported by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Healthcare Associated Infections and Antimicrobial Resistance at the University of Oxford, in partnership with Public Health England (PHE) (NIHR200915). A.S.W. and T.E.A.P. are also supported by the NIHR Oxford Biomedical Research Centre. E.P. and K.B.P. are also supported by the Huo Family Foundation. A.S.W. is also supported by core support from the Medical Research Council (MRC) UK to the MRC Clinical Trials Unit (MC_UU_12023/22A) and is an NIHR Senior Investigator. P.C.M. is funded by Wellcome (intermediate fellowship, grant no. 110110/Z/15/Z) and holds an NIHR Oxford BRC Senior Fellowship award. D.W.E. is supported by a Robertson Fellowship and an NIHR Oxford BRC Senior Fellowship. The views expressed are those of the authors and are not necessarily those of the National Health Service, the NIHR, the Department of Health or PHE. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. All authors had full access to all data analysis outputs (reports and tables) and take responsibility for their integrity and accuracy. We are grateful for the support of all COVID-19 Infection Survey participants and the COVID-19 Infection Survey team: Office for National Statistics: I. Diamond, E. Rourke, R. Studley, T. Thomas, D. Cook, D. Ayoubkhani, R. Black, A. Felton, M. Crees, J. Jones, L. Lloyd and E. Sutherland; University of Oxford, Nuffield Department of Medicine: A. S. Walker, D. Crook, P. C. Matthews, T. Peto, E. Pritchard, N. Stoesser, K.-D. Vihta, J. Wei, A. Howarth, G. Doherty, J. Kavanagh, K. K. Chau, S. B. Hatch, D. Ebner, L. Martins Ferreira, T. Christott, B. D. Marsden, W. Dejnirattisai, J. Mongkolsapaya, S. Cameron, P. Tamblin-Hopper, M. Wolna, R. Brown, S. Hoosdally, R. Cornall, D. I. Stuart and G. Screaton; University of Oxford, Nuffield Department of Population Health: K. Pouwels; University of Oxford, Big Data Institute: D. W. Eyre, K. Lythgoe, D. Bonsall, T. Golubchik and H. Fryer; University of Oxford, Radcliffe Department of Medicine: J. Bell; Oxford University Hospitals NHS Foundation Trust: S. Cox, K. Paddon and T. James; University of Manchester: T. House; Wellcome Trust: J. Farrar; Public Health England: J. Newton, J. Robotham and P. Birrell; IQVIA: H. Jordan, T. Sheppard, G. Athey, D. Moody, L. Curry and P. Brereton; National Biocentre: I. Jarvis, A. Godsmark, G. Morris, B. Mallick and P. Eeles; Glasgow Lighthouse Laboratory: J. Hay and H. VanSteenhouse; Department of Health and Social Care: J. Lee; Welsh Government: S. White, T. Evans and L. Bloemberg; Scottish Government: K. Allison, A. Pandya and S. Davis; Public Health Scotland: D. I. Conway, M. MacLeod and C. Cunningham.

Publisher Copyright:
© 2021, The Author(s).


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