Table 5.
Subgroup analysis of the association between influenza vaccination and SARS-CoV-2 infection.
| Subgroup Variables | No. of Studies | Adjusted Estimate (95% CI) | p-Value | I2 Value (%) |
|---|---|---|---|---|
| Study Design | ||||
| cross sectional study | 5 | 0.76 (0.75–0.77) | <0.01 | 0.00 |
| retrospective cohort study | 10 | 0.80 (0.75–0.86) | <0.01 | 41.5 |
| prospective cohort study | 4 | 0.80 (0.56–1.08) | 0.14 | 90.9 |
| case-control study | 3 | 0.99 (0.76–1.23) | 0.93 | 51.7 |
| Study Population | ||||
| adults-general population | 13 | 0.80 (0.74–0.87) | <0.01 | 68.4 |
| older adults | 3 | 0.72 (0.56–0.92) | 0.01 | 53.8 |
| health workers | 6 | 0.84 (0.68–1.04) | 0.12 | 66.6 |
| Effect Size | ||||
| OR | 17 | 0.80 (0.74–0.87) | <0.01 | 72.5 |
| RR/HR | 5 | 0.82 (0.73–0.92) | <0.01 | 46.4 |
| Adjustment Factors | ||||
| age/gender/age and gender | 5 | 0.86 (0.62–1.21) | 0.40 | 63.5 |
| age, gender and comorbidities | 9 | 0.82 (0.73–0.92) | <0.01 | 78.4 |
| age, gender, comorbidities, and socioeconomic status, education or residence | 6 | 0.87 (0.68–1.11) | 0.26 | 81.8 |
| COVID-19 test | ||||
| rt-PCR | 15 | 0.84 (0.77–0.92) | <0.01 | 57.7 |
| IgG/IgM antibodies | 2 | 0.83 (0.38–1.82) | 0.64 | 37.9 |
| Laboratory confirmed (not specified) | 5 | 0.74 (0.66–0.83) | <0.01 | 74.9 |
| Continent | ||||
| Europe | 13 | 0.81 (0.70–0.93) | <0.01 | 79.7 |
| N. America | 6 | 0.76 (0.75–0.77) | <0.01 | 0.00 |
| Asia | 3 | 0.83 (0.77–0.90) | <0.01 | 0.00 |