Table 2. Interim vaccine effectiveness estimates for influenza A(H3N2), Canadian Sentinel Practitioner Surveillance Network, 1 November 2016–21 January 2017 (n = 906).
| Model | n total | Cases | Controls | VE % (95% CI) |
||
|---|---|---|---|---|---|---|
| n | % vaccinated | n | % vaccinated | |||
| Primary analysisa | ||||||
| Unadjusted | 906 | 370 | 24 | 536 | 30 | 27 (1 to 46) |
| Individual covariate adjustment | ||||||
| Age group (1–8, 9–19, 20–49, 50–64, ≥ 65 years) | 30 (4 to 50) | |||||
| Provinceb | 32 (7 to 50) | |||||
| Specimen collection interval from ILI onset (≤ 4, 5–7 days) | 23 (−5 to 44) | |||||
| Specimen collection date (2-week interval) | 38 (15 to 55) | |||||
| Full covariate adjustment | ||||||
| Adjusted | 42 (18 to 59) | |||||
| Restricted by provincec | ||||||
| Alberta | ||||||
| Unadjusted | 278 | 110 | 18 | 168 | 30 | 49 (8 to 72) |
| Adjusted | 62 (26 to 80) | |||||
| British Columbia | ||||||
| Unadjusted | 327 | 134 | 28 | 193 | 29 | 4 (−56 to 41) |
| Adjusted | 28 (−30 to 60) | |||||
| Ontariod | ||||||
| Unadjusted | 179 | 87 | 29 | 92 | 42 | 45 (−2 to 71) |
| Adjusted | 27 (−60 to 66) | |||||
| Quebec | ||||||
| Unadjusted | 122 | 39 | 13 | 83 | 17 | 28 (−118 to 76) |
| Adjusted | NE | |||||
| All provinces excluding Alberta | ||||||
| Unadjusted | 628 | 260 | 26 | 368 | 29 | 16 (−19 to 42) |
| Adjustede | 34 (−1 to 57) | |||||
CI: confidence interval; ILI: influenza-like illness; NE: not estimated (insufficient sample size); VE: vaccine effectiveness.
a Analysis adjusted for age group, province, specimen collection interval from ILI onset and specimen collection date (2-week interval).
b Alberta, British Columbia, Ontario, Quebec.
c Analysis adjusted for age group, specimen collection interval and specimen collection date (2-week interval).
d Due to logistical issues, specimen collection for the 2016/17 season began late in Ontario. The study period for Ontario-specific VE analysis was defined as 12 December 2016 (week 50) to 21 January 2017 (week 3).
e Analysis adjusted for age group, province (British Columbia, Ontario, Quebec), specimen collection interval and specimen collection date (2-week interval).