Waning of first- and second-dose ChAdOx1 and BNT162b2 COVID-19 vaccinations: a pooled target trial study of 12.9 million individuals in England, Northern Ireland, Scotland and Wales


Several SARS-CoV-2 vaccines have been shown to provide protection against COVID-19 hospitalization and death. However, some evidence suggests that notable waning in effectiveness against these outcomes occurs within months of vaccination. We undertook a pooled analysis across the four nations of the UK to investigate waning in vaccine effectiveness (VE) and relative vaccine effectiveness (rVE) against severe COVID-19 outcomes.


We carried out a target trial design for first/second doses of ChAdOx1(Oxford–AstraZeneca) and BNT162b2 (Pfizer–BioNTech) with a composite outcome of COVID-19 hospitalization or death over the period 8 December 2020 to 30 June 2021. Exposure groups were matched by age, local authority area and propensity for vaccination. We pooled event counts across the four UK nations.


For Doses 1 and 2 of ChAdOx1 and Dose 1 of BNT162b2, VE/rVE reached zero by approximately Days 60–80 and then went negative. By Day 70, VE/rVE was –25% (95% CI: –80 to 14) and 10% (95% CI: –32 to 39) for Doses 1 and 2 of ChAdOx1, respectively, and 42% (95% CI: 9 to 64) and 53% (95% CI: 26 to 70) for Doses 1 and 2 of BNT162b2, respectively. rVE for Dose 2 of BNT162b2 remained above zero throughout and reached 46% (95% CI: 13 to 67) after 98 days of follow-up.


We found strong evidence of waning in VE/rVE for Doses 1 and 2 of ChAdOx1, as well as Dose 1 of BNT162b2. This evidence may be used to inform policies on timings of additional doses of vaccine.

Author list



  1. Centre for Medical Informatics, Usher Institute, The University of Edinburgh, Edinburgh, UK, 
  2. Population Data Science, Swansea University Medical School, Swansea University, Swansea, UK, 
  3. School of Medicine, Dentistry and Biomedical Sciences, Queen’s University Belfast, Belfast, UK, 
  4. Public Health Agency, Belfast, UK, 
  5. Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK, 
  6. Department of Education and Childhood Studies, Swansea University, Swansea, UK, 
  7. MRC/CSO Social & Public Health Sciences Unit, University of Glasgow, Glasgow, UK, 
  8. Public Health Scotland, Glasgow, UK, 
  9. Department of Mathematics and Statistics, University of Strathclyde, Glasgow, UK and 
  10. BREATHE—The Health Data Research Hub for Respiratory Health, The University of Edinburgh, Edinburgh, UK


Steven Kerr,1 Stuart Bedston,2 Declan T Bradley,3,4 Mark Joy,5 Emily Lowthian ,2,6 Rachel M Mulholland,1 Ashley Akbari,2 FD Richard Hobbs,5 Srinivasa Vittal Katikireddi,7 Simon de Lusignan,5 Igor Rudan,1 Fatemeh Torabi,Ruby SM Tsang,5 Ronan A Lyons,2 Chris Robertson,8,9 and Aziz Sheikh,1,10

Novel Coronavirus SARS-CoV-2


International Journal of Epidemiology