Table 2.
Associated risk and publication bias between influenza vaccination and the risk of SARS-CoV-2 infection.
| Egger's test | |||||||
| Studies | Number of studies | Cumulative sample size | OR (95% CI) | I2 (%) | Effect model | t | P value |
| Infection | 20 | 55,867,805 | 0.84 (0.75–0.96)∗ | 89 | Random | 0.99 | 0.34 |
| Adjusted estimate | 17 | 55,860,337 | 0.80 (0.73–0.87)∗ | 85 | Random | 0.41 | 0.68 |
| Population | |||||||
| General | 9 | 55,780,161 | 0.79 (0.71–0.87)∗ | 75 | Random | −0.10 | 0.92 |
| HCWs | 8 | 59,570 | 0.74 (0.59–0.93)∗ | 85 | Random | −2.66 | 0.04 |
| Elders | 6 | 55,718,816 | 0.76 (0.75–0.77)∗ | 0 | Fix | 0.94 | 0.40 |
| Study design | |||||||
| Cohort study | 8 | 147,844 | 0.83 (0.72–0.95)∗ | 88 | Random | −0.81 | 0.45 |
| Case-control study | 3 | 6013 | 0.80 (0.67–0.94)∗ | 0 | Fix | 0.44 | 0.74 |
| Cross-sectional study | 6 | 55,713,075 | 0.76 (0.75–0.77)∗ | 45 | Fix | −0.13 | 0.91 |
| Type of influenza vaccine | |||||||
| Quadrivalent | 8 | 56,433 | 0.74 (0.67–0.81)∗ | 71 | Random | −3.39 | 0.02 |
| Trivalent | 2 | 4429 | 1.00 (0.77–1.29) | 71 | Random | NA | |
| Inactivated | 5 | 35,101 | 0.77 (0.66–0.89)∗ | 59 | Random | −2.42 | 0.09 |
| Diagnostic approach | |||||||
| Polymerase chain reaction test | 13 | 85,704 | 0.87 (0.72–1.06) | 84 | Random | −0.88 | 0.40 |
| Serological test | 5 | 55,510 | 0.90 (0.75–1.08) | 74 | Random | −1.05 | 0.37 |
| Others/not mention | 5† | 55,732,954 | 0.48 (0.19–1.21) | 90 | Random | −0.96 | 0.41 |
∗
P < 0.05.
†
Including two original studies did not mention this information, one for pulmonologist-confirmed and two for laboratory confirmed but not specified it. CI: Confidence interval; COVID-19: Corona virus disease 2019; NA: Not available due to limited number of studies; OR: Odds ratio; SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2; HCWs: Healthcare workers.