Comparative effectiveness of ChAdOx1 versus BNT162b2 COVID-19 vaccines in Health and Social Care workers in England

A compararison of the effectiveness of the BNT162b2 mRNA (Pfizer-BioNTech) and the ChAdOx1 (Oxford-AstraZeneca) COVID-19 vaccines against infection and COVID-19 disease in health and social care workers.

The BMJ, 2022

Paper information

William J Hulme, Elizabeth J Williamson, Amelia Green, Krishnan Bhaskaran, Helen I McDonald, Christopher T Rentsch, Anna Schultze, John Tazare, Helen J Curtis, Alex J Walker, Laurie Tomlinson, Tom Palmer, Elsie Horne, Brian MacKenna, Caroline E Morton, Amir Mehrkar, Jessica Morley, Louis Fisher, Seb Bacon, Dave Evans, Peter Inglesby, George Hickman, Simon Davy, Tom Ward, Richard Croker, Rosalind M Eggo, Angel YS Wong, Rohini Mathur, Kevin Wing, Harriet Forbes, Daniel Grint, Ian J Douglas, Stephen JW Evans, Liam Smeeth, Chris Bates, Jonathan Cockburn, John Parry, Frank Hester, Sam Harper, Jonathan AC Sterne, Miguel Hernán, Ben Goldacre. BMJ 2022;378:e068946



To compare the effectiveness of the BNT162b2 mRNA (Pfizer-BioNTech) and the ChAdOx1 (Oxford-AstraZeneca) COVID-19 vaccines against infection and COVID-19 disease in health and social care workers.


Cohort study, emulating a comparative effectiveness trial.


Linked primary care, hospital, and COVID-19 surveillance records available within the OpenSAFELY-TPP research platform.


317,341 health and social care workers vaccinated between 4 January and 28 February 2021, registered with a GP practice using the TPP SystmOne clinical information system in England, and not clinically extremely vulnerable.


Vaccination with either BNT162b2 or ChAdOx1 administered as part of the national COVID-19 vaccine roll-out.

Main outcome measures

Recorded SARS-CoV-2 positive test, or COVID-19 related Accident and Emergency attendance or hospital admission occurring within 20 weeks of vaccination.


The cumulative incidence of each outcome was similar for both vaccines during the first 20 weeks post-vaccination. The cumulative incidence of recorded SARS-CoV-2 infection 6 weeks after vaccination with BNT162b2 was 19.2 per 1000 people (95%CI 18.6 to 19.7) and with ChAdOx1 was 18.9 (95%CI 17.6 to 20.3), representing a difference of -0.24 per 1000 people (95%CI -1.71 to 1.22). The difference in the cumulative incidence per 1000 people of COVID-19 accident and emergency attendance at 6 weeks was 0.01 per 1000 people (95%CI -0.27 to 0.28). For COVID-19 hospital admission, this difference was 0.03 per 1000 people (95%CI -0.22 to 0.27).


In this cohort of healthcare workers where we would not anticipate vaccine type to be related to health status, we found no substantial differences in the incidence of SARS-CoV-2 infection or COVID-19 disease up to 20 weeks after vaccination. Incidence dropped sharply after 3-4 weeks and there were very few COVID-19 hospital attendance and admission events after this period. This is in line with expected onset of vaccine-induced immunity, and suggests strong protection against COVID-19 disease for both vaccines.