Study: Effectiveness of BNT162b2 booster doses in England: an observational study in OpenSAFELY-TPP. Image Credit: Jo Panuwat D / Shutterstock

OpenSAFELY study shows effectiveness of Pfizer COVID booster doses

In a recent study published on medRxiv* preprint server, researchers assessed the effectiveness of the Pfizer-BioNTech BNT162b2 vaccine against coronavirus disease 2019 (COVID-19) in the seven million adults in the United Kingdom (UK) who were eligible to receive booster injections between September 16 and December 16, 2021.

Study: Efficacy of BNT162b2 booster doses in England: an observational study in OpenSAFELY-TPP. Image Credit: Jo Panuwat D/Shutterstock


As part of its national COVID-19 vaccination programme, the UK initially prioritized its high-risk population to receive boosters in September 2021 before being made available to its general adult population . However, following the emergence of Omicron Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variant of concern (VOC), the availability of boosters was reduced to three months on December 8, 2021. Previously, boosters were available six months after a person has received their second dose of the COVID-19 vaccine.

About the study

In the current study, researchers estimated the effectiveness of booster shots of the BNT162b2 vaccine in adults who received two doses of the vaccine between September 16 and December 16, 2021. The team used data from the database OpenSAFELY-TPP for study analysis. The database contained information on 40% of primary care practices in English linked to national coronavirus surveillance, hospital and death register data. Study follow-up continued for 10 weeks or December 31, 2021, where researchers compared each booster recipient with a matched unboosted control subject based on booster priority and prior vaccination status.

The team assigned a matched control to each study participant based on National Health Service (NHS) region, date of study entry, vaccine brand, and date of delivery. second dose of vaccine. A Cox regression model was fitted for these factors to estimate hazard ratios (HRs), where 1-HR expressed as a percentage indicated the effectiveness of BNT162b2 recall. HR estimates compared boosted to unboosted individuals, overall and separately, for days 1-28 and 29-70. Additionally, the team estimated HRs for days one-seven, eight-14, 15 to 28, 29 to 42, and 43 to 70. The study had multiple outcomes: one positive SARS-CoV-2 test, one COVID-19-related death, one COVID-19 hospitalization, and one non-COV-related death. COVID-19.

Study results

The study population consisted of 6,990,219 individuals matched as controls and then rematched in the booster group. As expected, the matching factors and the proportion of people with pre-existing morbidities were similar between the study groups. Although the standardized mean difference between the two groups was consistently less than 0.1, subjects in the control group had more learning disabilities, lower SARS-CoV-2 testing frequency, and higher rates of illness. severe mental illness and deprivation. Screening 23,151,145 person-weeks of follow-up yielded 123,378 positive SARS-CoV-2 tests, 3,672 COVID-19 hospitalizations, 588 COVID-19-related deaths, and 6,990 non-COVID-19-related deaths.

Boosted individuals showed an aberrant increase in the overall incidence of positive SARS-CoV-2 tests around seven days after receiving booster shots; however, they did not show a similar pattern for other severe COVID-19 outcomes. Additionally, differences in the overall incidence of positive SARS-CoV-2 tests between the study groups were apparent within the first few days.

Accordingly, the 10-week risk of a positive SARS-CoV-2 test in the boosted versus unboosted group was 47.3 and 84.0 per 1000, respectively, corresponding to a risk difference of 36 .8 per 1000. The risk difference for COVID-19 hospitalization, COVID-19 related deaths and non-COVID-19 related deaths were 3.6, 1 and 8.1 respectively.

The recall (overall) effectiveness for days one through seven was 50.7%, 80.1%, 88.5%, and 80.3% for positive SARS-CoV-2 test, hospitalization COVID- 19, COVID-19 death and non-COVID-19 death. Additionally, recall effectiveness against all COVID-19 outcomes was generally lower during days 1-28 than between days 29-70. SARS-CoV-2 positives appeared to decline about six weeks after the booster. vaccination, 68.2% versus 45.3% between days 15-28 and days 43-70.


Overall, a booster injection of BNT162b2 reduced rates of positive tests for SARS-CoV-2 by approximately 50% in the first 10 weeks after the booster was given. Additionally, booster shots reduced rates of COVID-19 hospitalization, COVID-19-related death, and non-COVID-19-related death. More importantly, booster efficacy remained similar against all severe COVID-19 outcomes, regardless of vaccine brand used for primary vaccination and prior infection.

Conversely, estimated booster effectiveness was lower in those under 65 and clinically vulnerable populations. Given that the current study showed evidence of decreasing booster efficacy against positive SARS-CoV-2 tests, the authors emphasized the need to monitor booster vaccine efficacy over time.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.


  • Efficacy of BNT162b2 booster doses in England: an observational study in OpenSAFELY-TPP, William J Hulme, Elizabeth J Williamson, Elsie Horne, Amelia CA Green, Linda Nab, Ruth Keogh, Edward PK Parker, Venexia M Walker, Tom M Palmer , Helen J Curtis, Milan Wiedemann, Christine Cunningham, Alex J Walker, Louis Fisher, Brian MacKenna, Christopher T Rentsch, Anna Schultze, Krishnan Bhaskaran, John Tazare, Laurie A Tomlinson, Helen I McDonald, Caroline E Morton, Richard Croker, Colm D Andrews, Lisa EM Hopcroft, Robin Y Park, Jon Massey, Amir Mehrkar, Jessica Morley, Sebastian CJ Bacon, David Evans, Peter Inglesby, George Hickman, Simon Davy, Iaim Dillingham, Tom Ward, Viyaasan Mahalingasivam, Bang Zheng, Ian J Douglas, Stephen JW Evans, Christopher Bates, Jonathan AC Sterne, Miguel A Hernan, Ben Goldacre, preprint medRxiv 2022, DOI:,

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