Table 2.
Influenza incidence in the 2020 and 2014–2019 seasons by social-distancing period
| Week no | W1 ~ W3 | W4 ~ W10 | W11 ~ 16 | W17 ~ 33 | W34 ~ 41 | W42 ~ 47 | W48 ~ 52 |
|---|---|---|---|---|---|---|---|
| 20.1.1 ~ 1.18 | 1.19 ~ 2.7 | 2.8 ~ 2.18 | 2.19 ~ 8.15 | 8.16 ~ 10.10 | 10.11 ~ 11.21 | 11.22 ~ 12.31 | |
| Before COVID-19 | Alert level red | Pandemic declared, Enhanced SD | Relaxed, Daily life, SD 1 | SD 2, 2.5 | SD 1 | SD 2, 2.5, 3 | |
| ILI/1000 outpatients | |||||||
| 2020 | |||||||
| Mean | 46.43 | 16.51 | 2.73 | 2.04 | 1.58 | 2.40 | 2.67 |
| Median | 47.80 | 11.60 | 2.75 | 2.00 | 1.45 | 2.50 | 2.70 |
| IQR | 3.35 | 14.80 | 0.33 | 0.50 | 0.40 | 1.43 | 0.28 |
| 2014–2019 | |||||||
| Mean | 29.95 | 26.74 | 20.68 | 5.72 | 3.82 | 5.38 | 29.67 |
| Median | 23.05 | 27.90 | 19.40 | 4.70 | 3.85 | 4.55 | 19.20 |
| IQR | 23.20 | 31.05 | 17.68 | 1.78 | 0.90 | 2.00 | 41.00 |
| Percent reduction | -55.04 | 38.23 | 86.78 | 64.32 | 58.74 | 55.40 | 91.01 |
| Mean difference | 16.48 | -10.22 | -17.94 | -3.68 | -2.24 | -2.98 | -25.57 |
| p-value | 0.206 | 0.132 | < 0.005 | < 0.005 | < 0.005 | < 0.005 | < 0.05 |
| Number of detected IFV All (A/H1N1, A/H3N2, B) | |||||||
| 2020 | |||||||
| Mean | 125.00 | 46.29 | 0.00 | 0.12 | 0.00 | 0.00 | 0.00 |
| Median | 126.00 | 35.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| IQR | 6.50 | 65.50 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| 2014–2019 | |||||||
| Mean | 83.22 | 85.98 | 68.58 | 6.22 | 0.90 | 6.17 | 60.32 |
| Median | 79.00 | 92.50 | 67.00 | 2.00 | 0.50 | 2.00 | 50.00 |
| IQR | 55.00 | 94.50 | 57.25 | 5.00 | 1.00 | 8.00 | 99.50 |
| Percent reduction | -50.20 | 46.16 | 100.00 | 98.10 | 100.00 | 100.00 | 100.00 |
| Mean difference | 41.78 | -39.69 | -68.58 | -6.10 | -0.90 | -6.17 | -56.72 |
| p-value | 0.204 | 0.101 | < 0.005 | < 0.005 | < 0.005 | 0.117 | < 0.05 |
| IFV positivity rate | |||||||
| 2020 | |||||||
| Mean | 40.53 | 17.58 | 0.00 | 0.16 | 0.00 | 0.00 | 0.00 |
| Median | 40.56 | 15.84 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| IQR | 2.93 | 26.16 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| 2014–2019 | |||||||
| Mean | 31.74 | 34.81 | 26.18 | 2.69 | 0.45 | 2.40 | 20.81 |
| Median | 31.14 | 39.02 | 26.89 | 1.00 | 0.21 | 0.83 | 16.67 |
| IQR | 21.72 | 38.34 | 22.10 | 2.59 | 0.61 | 3.08 | 32.26 |
| Percent reduction | -27.68 | 49.49 | 100.00 | 94.13 | 99.78 | 99.96 | 100.00 |
| Mean difference | 8.79 | -17.23 | -26.18 | -2.53 | -0.44 | -2.40 | -19.67 |
| p-value | 0.390 | 0.0566 | < 0.005 | < 0.005 | 0.0511 | 0.0981 | < 0.05 |
aILI Influenza-like illness, IFV Influenza virus, IFV Positivity rate, number of detected IFVs /total specimens, IQR Interquartile range, SD Social distancing
Percentage reduction: (mean of 2014–2019 − mean of 2020) ÷ (mean of 2014–2019) × 100
bW1–3: before COVID-19, W4–10: alert level red, W11–16: pandemic declared, SD, W16–33: relaxed SD, distancing in daily life, Level 1 SD, W34–41: Level 2 SD, W42–47: Level 1, 1.5 SD, W48–52: Level 2, 2 + a, 2.5 SD
cDetailed summary of social distancing (Table S1)