| Study and publication date | Country | Study design | Study population (n) | Age (years) | Vaccine(s) | Time point of analysis after full vaccination schedule | Adjusted vaccine efficacy/effectiveness (95% CI) |
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|---|---|---|---|---|---|---|---|---|---|---|
| Alpha (sequenced) | Delta (sequenced) | Alpha-dominance | Delta-dominance | |||||||
| Infection (any type)a | ||||||||||
| Elliott [10]; 4 August 2021b |
UK | Serial cross-sectional design | General population (n = 57,457) | 18–64 | NR | NR | NA | NA | NA | 49% (22–67) |
| Fowlkes [19]; 24 August 2021 |
US | Cohort study | Frontline workers (HCW and other essential and frontline workers) (n = 4,217), of which 3,483 were vaccinated. (Comirnaty: n = 2,278; Spikevax: n = 1,138; Janssen: n = 67) | ≥ 18 | Comirnaty; Spikevax; COVID-19 Vaccine Janssen | ≥ 14 days | NA | NA | 91% (81–96) | 66% (26–84) |
| Nanduri [16]; 18 August 2021 |
US | Cohort study | Care home residents (Delta-dominance: 5,011,746 vaccinated and 953,861 unvaccinated; Alpha-dominance: 936,123 vaccinated and 217,534 unvaccinated) | Elderly peoplec | Comirnaty; Spikevax | ≥ 14 days | NA | NA | Corminaty: 74.2% (68.9–78.7); Spikevax: 74.7% (66.2–81.1) | Comirnaty: 52.4% (48.0–56.4); Spikevax: 50.6% (45.0–55.7) |
| Pouwels [4]; 24 August 2021b |
UK | Cohort study | Household members (n = 384,543 for Alpha dominant period; 358,983 during Delta-dominant period) | ≥ 18c | Comirnaty; Vaxzevria | ≥ 14 days | NA | NA | Comirnaty: 78% (68–84); Vaxzevria: 79% (56–90) | Corminaty: 80% (77–83); Vaxzevria: 67% (62–71) |
| Household members (n = 358,983) | 18–64 | Comirnaty; Vaxzevria | ≥ 14 days | NA | NA | NA | Comirnaty: all age groups: 82% (79–85) 18–34 years: 90% (85–93%) 35–64 years: 77% (65–85%) Vaxzevria: all age groups: 67% (62–71) 18–34 years: 73% (65–80%) 35–64 years: 54% (40–65%) |
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| Pramod [9]; 22 July 2021b |
India | Test-negative design | HCW (n = 360 case–control pairs) | Median age: Cases: 34 (28–43), Controls: 33 (28–42) | Covishield | ≥ 14 days | NA | NA | NA | 54% (27–71) |
| Puranik [5]; 21 August 2021b |
US | Cohort study | Vaccinated persons tested for SARS-CoV-2 at Mayo Clinic and affiliated hospitals (Comirnaty: n = 119,463; Spikevax: n = 60,083) | ≥ 18c | Comirnaty; Spikevax | ≥ 14 days | NA | NA | Comirnaty: 76% (69–81); Spikevax: 86% (81–90.6) | Comirnaty: 42% (13–62); Spikevax: 76% (58–87) |
| Rosenberg [6]; 18 August 2021 |
US | Serial cross-sectional design | General population (10,135,322 vaccinated and 3,742,197 unvaccinated) | ≥ 18c | NR | ≥ 14 days | NA | NA | 91.7% | 79.8% |
| Sheikh [17]; 14 June 2021 |
UK | Test-negative design | General population (Delta: 53,679 vaccinated with Comirnaty and 32,719 vaccinated with Vaxzevria, 953,861 unvaccinated; Alpha: 53,575 vaccinated with Comirnaty and 32,588 vaccinated with Vaxzevria, 119,419 unvaccinated) | ≥ 18c | Comirnaty; Vaxzevria | ≥ 14 days | Comirnaty: 92% (90–93); Vaxzevria: 73% (66–78) | Comirnaty: 79% (75–82); Vaxzevria: 60% (53–66) | NA | NA |
| Tang [8]; 11 August 2021b |
Qatar | Test-negative design | Resident population (Comirnaty: n = 877,354; Spikevax: n = 409,041) | ≥ 18c | Comirnaty; Spikevax | ≥ 14 days | NA | Comirnaty: 59.6% (50.7–66.9) Spikevax: 86.1% (78.0–91.3) |
NA | NA |
| Tartof [7]; 23 August 2021b |
US | Cohort study | Insurance members (n = 3,436,957) | ≥ 12 | Comirnaty | ≥ 7 days | 91% (88‒92) | 75% (71‒78) | NA | NA |
| Asymptomatic infection | ||||||||||
| Pouwels [4]; 24 August 2021b |
UK | Cohort study | Household members (n = 358,983) | 18–64 | Comirnaty; Vaxzevria | ≥ 14 days | NA | NA | NA | Comirnaty: 74% (69–78) Vaxzevria: 57% (51–63) |
| Tang [8]; 11 August 2021b |
Qatar | Test-negative design | Resident population; (Comirnaty: 877,354; Spikevax: 409,041) | ≥ 18c | Comirnaty; Spikevax | ≥ 14 days | NA | Comirnaty: 35.9% (11.1–53.9) Spikevax: 80.2% (54.2–92.6) | NA | NA |
CI: confidence interval; COVID-19: coronavirus disease; HCW: healthcare workers; NA: not applicable; NR: not reported; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; UK: United Kingdom; US: United States. a Not reported whether these were symptomatic or asymptomatic infections. b Preprint. c Exact age not provided. Comirnaty (BNT162b2 mRNA, BioNTech-Pfizer, Mainz, Germany/New York, United States (US)), Spikevax (mRNA-1273, Moderna, Cambridge, US), Vaxzevria (ChAdOx1 nCoV-19, Oxford-AstraZeneca, Cambridge, United Kingdom (UK), COVID-19 Vaccine Janssen (Ad26.COV2-S, Janssen-Cilag International NV, Beerse, Belgium). Covishield (Vaxzevria, Serum Institute of India, Pune, India). | ||||||||||