Table 1.
Baseline characteristics of the 21 publications, involving 22 studies that assessed the association between influenza vaccination and SARS-CoV-2 infection.
| First Author’s Name | Year of Publication | Country | Identification of COVID-19 | Sample Size | Effect Size | Adjusted Estimate |
|---|---|---|---|---|---|---|
| M. Noale et al. [38] | 2020 | Italy | rt-PCR | 6061 | OR | 0.85 (95% CI: 0.74–0.98) |
| M. Noale et al. [38] | 2020 | Italy | rt-PCR | 619 | OR | 0.87 (95% CI: 0.59–1.28) |
| I. Martínez-Baz et al. [29] | 2020 | Spain | rt-PCR or Antibody Rapid test | 9745 | OR | 1.07(95% CI: 0.92–1.24) |
| P. Ragni et al. [40] | 2020 | Italy | rt-PCR | 17,608 | OR | 0.89 (95% CI: 0.80–0.99) |
| M. Belingheri et al. [31] | 2020 | Italy | rt-PCR | 3520 | OR | 0.41 (95% CI: 0.07–2.39) |
| A. Vila-Córcoles et al. [41] | 2020 | Spain | rt-PCR | 79,083 | HR | 1.02 (95% CI: 0.79–1.32) |
| I. Green et al. [42] | 2020 | Israel | rt-PCR | 19,089 | OR | 0.79 (95% CI: 0.67–0.98) |
| E. Kissling et al. [15] | 2021 | Europe | rt-PCR | 2147 | OR | 0.93 (95% CI: 0.66–1.32) |
| A. Conlon et al. [43] | 2021 | USA | rt-PCR | 27,201 | OR | 0.76 (95% CI: 0.68–0.86) |
| B. Erismis et al. [33] | 2021 | Turkey | Not specified | 203 | RR | 0.83 (95% CI: 0.75–0.93) |
| A. Bozek et al. [44] | 2021 | Poland | rt-PCR | 2558 | HR | 0.74 (95% CI: 0.54–0.89) |
| M. Kowalska et al. [45] | 2021 | Poland | IgG antibodies | 5376 | OR | 0.68 (95% CI: 0.55–0.83) |
| M. Fernández-Prada et al. [46] | 2021 | Spain | rt-PCR | 188 | OR | 1.70 (95% CI: 0.97–3.25) |
| K. Huang et al. [37] | 2021 | USA | Not specified | 55,667.997 | OR | 0.76 (95% CI: 0.75–0.77) |
| J. P. King et al. [47] | 2021 | USA | rt-PCR | 1356 | OR | 0.83 (95% CI: 0.63–1.10) |
| C. Pawlowski et al. [48] | 2021 | USA | rt-PCR | 12,791 | RR | 0.85 (95% CI: 0.75–0.96) |
| S. Caratozzolo et al. [36] | 2020 | Italy | rt-PCR/or infection according to WHO definition | 848 | OR | 0.47 (95% CI: 0.29–0.74) |
| M. N. Rivas et al. [32] | 2021 | USA | IgG antibodies | 6087 | OR | 1.84 (95% CI: 0.57–11.3) |
| J. G. Zein et al. [49] | 2020 | USA | Not specified | 13,220 | OR | 0.79 (95% CI: 0.62–1.00) |
| P. A. Debisarun et al. [50] | 2020 | Netherlands | rt-PCR | 6856 | RR | 0.61 (95% CI: 0.46–0.82) |
| Y. Xiang et al. [51] | 2020 | UK | Laboratory confirmed | 30,835 | OR | 0.60 (95% CI: 0.53–0.68) |
| M. Alkathlan et al. [52] | 2021 | Saudi Arabia | Laboratory confirmed | 424 | OR | 0.83 (95% CI: 0.51–1.35) |
OR = adjusted odds ratio, HR = hazard odds ratio, RR = relative risk, rt-PCR = Reverse transcription polymerase chain reaction.