Table 1 Characteristics of included studies showing effectiveness of BNT162b2 and ChAdOx1 COVID-19 vaccines

Israel

Dangan et al. (2021)

Retrospective

596,618

Effectiveness increased with increase in time, and with receipt of second dose

Effectiveness against symptomatic COVID-19 was 57% after 14–20 days and 66% after 21–27 days

–

Short follow-up after second dose, potential selection bias, risk of potential confounders, Potential exclusion of some eligible participants as a result of efforts to match

Israel

Chodlick et al. (2021)

Retrospective

503,875 (≥ 16 years)

51% effectiveness after within 24 days of first dose, effectiveness increased with increase in time

–

Potential unreported vaccination among potential eligible participants, not peer-reviewed as at the time of this review

England

Barnal et al. (2021a)

Retrospective

174,731 (≥ 70 years old)

Single dose was 80% effective at preventing hospitalisation, 85% effective at preventing COVID-19 related death

Single dose was 80% effective at preventing hospitalisation

Inherent limitations of observational study, potential confounders, yet to be peer-reviewed as at the time of this review

Denmark

Moutsen-Helms et al. (2021)

Retrospective

39,040 persons of 77–90 years and 33 039 persons of 36–57 years old

Protective effect was absent in older persons after first dose. Vaccine effectiveness was higher in the younger population (90%) than in older persons (64%) after 7 days of second vaccine dose

–

Study was not peer-reviewed as at the time of this study, observed variation in vaccine effectiveness may have been influenced by the large variation in sample size of the groups and potential confounders

Scotland

Vasileiou et al. (2021)

Retrospective

1,331 993 (Mean age of 65 years old)

First dose was associated with 91% reduced COVID-19—related hospitalisation at 28–34 days after vaccination

First dose was associated with 88% reduced COVID-19—related hospitalisation at 28–34 days after vaccination

Risk of potential confounders

England

Bernal et al. (2021b)

Retrospective

48,096 (≥ 70 years old)

Associated 44% and 69% reduced risk of death with one and two respective doses of BNT162b2 vaccination among COVID-19 cases

Associated 55% reduced risk of death from COVID-19

Insufficient follow-up to ascertain effects of second dose of ChAdOx1 vaccine on risk of death. Yet to be peer-reviewed at the time of this study

England

Shroti et al. (2021)

Retrospective

10,412 (older adults)

Reduction in SARS-CoV-2 infection after first and second dose

Reduction in SARS-CoV-2 infection after first and second dose

Study was yet to be peer-reviewed as at the time of this review. Risk of potential confounder bias may also be associated with the study

England

Hall et al. 2021

Prospective

23,324 (median age = 46.1)

Associated with 72% effectiveness after 21 days of first dose, and 86% effectiveness seven days after second dose

–

Risk of potential confounders

United Kingdom

Pritchard et al. (2021)

Retrospective

383,812 (≥ 16 years old)

Reduced SARS-CoV-2 infections ≥ 21 days after the first dose at 66% and 80% after second dose

Reduced SARS-CoV-2 infections ≥ 21 days after the first dose at 61% and 79% after second dose

Risk of potential confounders

Israel

Haas et al. (2021)

Retrospective

(≥ 16 years old)

Associated with 95.3% preventing incidence of SARS-CoV-2 7 days after second dose, 97.2% and 96.7% against COVID-19 related hospitalisation and death respectively

–

Risk of potential confounders

England

Bernal et al. (2021)

Retrospective

12,675

Dose effectiveness of BNT162b2 reduced from 93.4% with B.1.1.7 to 87.9% with B.1.6172.2

Associated effectiveness of two doses reduced 66.1% with B.1.1.7 to 59.8% with B.1.6172.2

Potential misclassification of cases and control may have been influenced by sensitivity and specificity of the PCR, paper was yet to be validated by peer-review as at the time of this review