Table 2.
Baseline characteristics of the 17 publications involving studies that assessed the association between influenza vaccination and COVID-19 clinical outcomes: (15 studies for hospitalization, four for Mechanical Ventilation/invasive respiratory support, 11 for Intensive care and 18 for mortality).
| First Author’s Name | Year of Publication | Country | Identification of COVID-19 | Sample Size | Effect Size | Adjusted Estimate |
|---|---|---|---|---|---|---|
| Hospitalization | ||||||
| P. D. Pedote et al. [53] | 2021 | Italy | rt-PCR | 662 | OR | 1.20 (95% CI: 0.70–1.90) |
| R. Pastorino et al. [39] | 2021 | Italy | rt-PCR | 741 | OR | 1.03 (95% CI: 0.66–1.62) |
| C. Pawlowski et al. [48] | 2021 | USA | rt-PCR | 959 | RR | 1.10 (95% CI: 0.83–1.50) |
| M. Gobbato et al. [54] | 2020 | Italy | Laboratory confirmed | 3010 | OR | 0.78 (95% CI: 0.61–1.01) |
| M-J. Yang et al. [55] | 2020 | USA | Laboratory confirmed | 2005 | OR | 0.41 (95% CI: 0.28–0.59) |
| S. Greco et al. [56] | 2021 | Italy | rt-PCR | 952 | OR | 1.44 (95% CI: 1.01–2.05) |
| A. Bozek et al. [44] | 2021 | Poland | rt-PCR | 151 | HR | 0.48 (95% CI: 0.36–0.77) |
| K. Huang et al. [37] | 2021 | USA | Not specified | 55,667,977 | OR | 0.76 (95% CI: 0.75–0.77) |
| M. Massari et al. [57] | 2021 | Italy | rt-PCR | 115,945 | RR | 0.87 (95% CI: 0.86–0.88) |
| A. Conlon et al. [43] | 2021 | USA | rt-PCR | 1218 | OR | 0.58 (95% CI: 0.46–0.73) |
| P. Ragni et al. [40] | 2020 | Italy | rt-PCR | 4485 | HR | 1.00 (95% CI: 0.84–1.19) |
| C. R. Wilcox et al. [58] | 2021 | UK | rt-PCR | 6921 | HR | 0.85 (95% CI: 0.75–0.97) |
| J. G. Zein et al. [49] | 2020 | USA | Not specified | 1434 | OR | 1.29 (95% CI: 0.72–2.31) |
| I. Ilic et al. [59] | 2020 | Serbia | rt-PCR | 107 | OR | 1.31 (95% CI: 0.54–3.17) |
| S. M. Taghioff et al. [60] | 2021 | Netherlands | Not specified | 74,754 | OR | 1.07 (95% CI: 0.96–1.18) |
| Mechanical Ventilation/Invansive Respiratory Support | ||||||
| G. Fink et al. [61] | 2020 | Brazil | rt-PCR | 39,745 | OR | 0.83 (95% CI: 0.77–0.89) |
| A. Conlon et al. [43] | 2021 | USA | rt-PCR | 1218 | OR | 0.45 (95% CI: 0.27–0.78) |
| A. E. Demkina et al. [62] | 2020 | Russia | Clinically confirmed/ rt-PCR |
214,751 | OR | 0.74 (95% CI: 0.54–1.01) |
| A. Bozek et al. [44] | 2021 | Poland | rt-PCR | 21 | OR | 0.42 (95% CI: 0.02–9.96) |
| Intensive Care | ||||||
| M-J. Yang et al. [55] | 2021 | USA | rt-PCR | 2005 | OR | 0.31 (95% CI: 0.07–0.85) |
| M. Massari et al. [57] | 2021 | Italy | rt-PCR | 111,740 | RR | 1.01 (95% CI: 0.99–1.04) |
| R. Pastorino et al. [39] | 2021 | Italy | rt-PCR | 99 | OR | 1.26 (95% CI: 0.74–2.21) |
| A. Conlon et al. [43] | 2021 | USA | rt-PCR | 1218 | OR | 0.64 (95% CI: 0.41–1.00) |
| C. Pawlowski et al. [48] | 2021 | USA | rt-PCR | 959 | RR | 1.10 (95% CI: 0.56–2.20) |
| G. Fink et al. [61] | 2020 | Brazil | rt-PCR | 39,156 | OR | 0.93 (95% CI: 0.87–0.99) |
| A. E. Demkina et al. [62] | 2020 | Russia | Clinically confirmed/ rt-PCR |
214,751 | OR | 0.76 (95% CI: 0.59–0.97) |
| M. Candelli et al. [63] | 2021 | Italy | rt-PCR | 602 | OR | 0.73 (95% CI: 0.35–1.56) |
| M. L. de la Cruz Contyet al. [34] | 2021 | Spain | rt-PCR | 206 | OR | 1.92 (95% CI: 0.36–10.3) |
| J. G. Zein et al. [49] | 2020 | USA | Not specified | 1434 | OR | 0.65 (95% CI: 0.22–1.79) |
| S. M. Taghioff et al. [60] | 2021 | Netherlands | Not specified | 74,754 | OR | 1.18 (95% CI: 1.00–1.39) |
| Mortality | ||||||
| S. Greco et al. [56] | 2021 | Italy | rt-PCR | 952 | OR | 1.06 (95% CI: 0.60–1.88) |
| P. D. Pedote et al. [53] | 2021 | Italy | rt-PCR | 662 | OR | 1.60 (95% CI: 0.80–3.20) |
| R. Pastorino et al. [39] | 2021 | Italy | rt-PCR | 97 | OR | 1.33 (95% CI: 0.77–2.31) |
| M. Massari et al. [57] | 2021 | Italy | rt-PCR | 115,945 | RR | 1.04 (95% CI: 1.01–1.06) |
| J. M. Fernadez. Ibánez et al. [64] | 2021 | Spain | rt-PCR | 410 | OR | 1.55 (95% CI: 0.96–2.48) |
| A. Bozek et al. [44] | 2021 | Poland | rt-PCR | 2558 | HR | 0.74 (95% CI: 0.03–20.8) |
| M. Candelli et al. [63] | 2021 | Italy | rt-PCR | 602 | OR | 0.20 (95% CI: 0.08–0.51) |
| A. Conlon et al. [43] | 2021 | USA | rt-PCR | 1218 | HR | 0.94 (95% CI: 0.61–1.47) |
| P. Ragni et al. [40] | 2020 | Italy | rt-PCR | 4872 | HR | 1.14 (95% CI: 0.95–1.37) |
| C. R Wilcox et al. [58] | 2021 | UK | rt-PCR | 6368 | OR | 0.76 (95% CI: 0.64–0.90) |
| G. Fink et al. [61] | 2020 | Brazil | rt-PCR | 53,752 | OR | 0.84 (95% CI: 0.78–0.91) |
| A. E. Demkina et al. [62] | 2020 | Russia | Clinically confirmed/ rt-PCR |
117,346 | HR | 0.78 (95% CI: 0.63–0.95) |
| Y. Azzi et al. [35] | 2020 | USA | rt-PCR | 229 | OR | 0.88 (95% CI: 0.70–0.96) |
| M. Gobbato et al. [54] | 2020 | Italy | Laboratory confirmed | 3010 | OR | 0.78 (95% CI: 0.61–1.01) |
| J. G. Zein et al. [49] | 2020 | USA | Not specified | 14,654 | OR | 0.98 (95% CI: 0.39–2.43) |
| D. Giannoglou et al. [65] | 2020 | Greece | Not specified | 512 | OR | 0.38 (95% CI: 0.17–0.81) |
| E. Ortiz-Prado et al. [66] | 2020 | Ecuador | rt-PCR | 9468 | RR | 1.40 (95% CI: 0.46–4.28) |
| S. M. Taghioff et al. [57] | 2021 | Netherlands | Not specified | 74,754 | OR | 0.89 (95% CI: 0.77–1.03) |