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Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK

Voysey, Merryn; Clemens, Sue Ann Costa; Madhi, Shabir A.; Weckx, Lily Y.; Folegatti, Pedro M.; Aley, Parvinder K.; Angus, Brian; Baillie, Vicky L.; Barnabas, Shaun L.; Bhorat, Qasim E.; Bibi, Sagida; Briner, Carmen; Cicconi, Paola; Collins, Andrea M.; Colin-Jones, Rachel; Cutland, Clare L.; Darton, Thomas C.; Dheda, Keertan; Duncan, Christopher J.A.; Emary, Katherine R.W.; Ewer, Katie J.; Fairlie, Lee; Faust, Saul N.; Feng, Shuo; Ferreira, Daniela M.; Finn, Adam; Goodman, Anna L.; Green, Catherine M.; Green, Christopher A.; Heath, Paul T.; Hill, Catherine; Hill, Helen; Hirsch, Ian; Hodgson, Susanne H.C.; Izu, Alane; Jackson, Susan; Jenkin, Daniel; Joe, Carina C.D.; Kerridge, Simon; Koen, Anthonet; Kwatra, Gaurav; Lazarus, Rajeka; Lawrie, Alison M.; Lelliott, Alice; Libri, Vincenzo; Lillie, Patrick J.; Mallory, Raburn; Mendes, Ana V.A.; Milan, Eveline P.; Minassian, Angela M.; McGregor, Alastair; Morrison, Hazel; Mujadidi, Yama F.; Nana, Anusha; O'Reilly, Peter J.; Padayachee, Sherman D...

Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK Thumbnail


Merryn Voysey

Sue Ann Costa Clemens

Shabir A. Madhi

Lily Y. Weckx

Pedro M. Folegatti

Parvinder K. Aley

Brian Angus

Vicky L. Baillie

Shaun L. Barnabas

Qasim E. Bhorat

Sagida Bibi

Carmen Briner

Paola Cicconi

Andrea M. Collins

Rachel Colin-Jones

Clare L. Cutland

Thomas C. Darton

Keertan Dheda

Christopher J.A. Duncan

Katherine R.W. Emary

Katie J. Ewer

Lee Fairlie

Saul N. Faust

Shuo Feng

Daniela M. Ferreira

Adam Finn

Anna L. Goodman

Catherine M. Green

Christopher A. Green

Paul T. Heath

Catherine Hill

Helen Hill

Ian Hirsch

Susanne H.C. Hodgson

Alane Izu

Susan Jackson

Daniel Jenkin

Carina C.D. Joe

Simon Kerridge

Anthonet Koen

Gaurav Kwatra

Rajeka Lazarus

Alison M. Lawrie

Alice Lelliott

Vincenzo Libri

Patrick J. Lillie

Raburn Mallory

Ana V.A. Mendes

Eveline P. Milan

Angela M. Minassian

Alastair McGregor

Hazel Morrison

Yama F. Mujadidi

Anusha Nana

Peter J. O'Reilly

Sherman D. Padayachee

Ana Pittella

Emma Plested

Katrina M. Pollock

Maheshi N. Ramasamy

Sarah Rhead

Alexandre V. Schwarzbold

Nisha Singh

Andrew Smith

Rinn Song

Matthew D. Snape

Eduardo Sprinz

Rebecca K. Sutherland

Richard Tarrant

Emma C. Thomson

Mark Toshner

Clinical Associate Professor

Johan Vekemans

Tonya L. Villafana

Marion E.E. Watson

Christopher J. Williams

Alexander D. Douglas

Adrian V.S. Hill

Teresa Lambe

Sarah C. Gilbert

Andrew J. Pollard

Marites Aban

Fatola Abayomi

Kushala Abeyskera

Jeremy Aboagye

Matthew Adam

Kirsty Adams

James Adamson

Yemi A. Adelaja

Syed Adlou

Khatija Ahmed

Yasmeen Akhalwaya

Saajida Akhalwaya

Andrew Alcock

Aabidah Ali

Elizabeth R. Allen

Lauren Allen

Thamires C.D.S.C. Almeida

Mariana P.S. Alves


© 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license Background: A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. Methods: This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and, NCT04324606, NCT04400838, and NCT04444674. Findings: Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0–75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4–97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8–80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3–4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. Interpretation: ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials. Funding: UK Research and Innovation, National Institutes for Health Research (NIHR), Coalition for Epidemic Preparedness Innovations, Bill & Melinda Gates Foundation, Lemann Foundation, Rede D'Or, Brava and Telles Foundation, NIHR Oxford Biomedical Research Centre, Thames Valley and South Midland's NIHR Clinical Research Network, and AstraZeneca.


Voysey, M., Clemens, S. A. C., Madhi, S. A., Weckx, L. Y., Folegatti, P. M., Aley, P. K., …Alves, M. P. (2021). Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK. Lancet, 397(10269), 99-111.

Journal Article Type Article
Acceptance Date Dec 3, 2020
Online Publication Date Dec 8, 2020
Publication Date 2021-01
Deposit Date Jan 22, 2021
Publicly Available Date Jan 22, 2021
Journal The Lancet
Print ISSN 0140-6736
Electronic ISSN 1474-547X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 397
Issue 10269
Pages 99-111
Keywords General Medicine
Public URL
Publisher URL
Additional Information This article is maintained by: Elsevier; Article Title: Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK; Journal Title: The Lancet; CrossRef DOI link to publisher maintained version:; CrossRef DOI link to the associated document:; Content Type: article; Copyright: © 2020 The Author(s). Published by Elsevier Ltd.


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