TABLE 1.
Influenza vaccine effectiveness stratified by age cohort.
| Controls (influenza test negative) a | Cases (influenza test positive) a | VE b (95% CI) | |||
|---|---|---|---|---|---|
| Unvacc | Vacc | Unvacc | Vacc | ||
| Ages 2–17 | |||||
| All vaccinated | 1181 | 502 | 437 | 61 | 66% (53%–76%) |
| By vaccine type | |||||
| LAIV | 1181 | 455 | 437 | 52 | 68% (55%–78%) |
| By influenza type | |||||
| A(H1N1)pdm09 | 1181 | 502 | 85 | 9 | 73% (43%–87%) |
| A(H3N2) | 1181 | 502 | 288 | 47 | 59% (40%–72%) |
| B | 1181 | 502 | 44 | < 3 | 95% (62%–99%) |
| Ages 18–64 | |||||
| All vaccinated | 5001 | 1994 | 1412 | 294 | 47% (37%–56%) |
| By vaccine type | |||||
| IIVe | 5001 | 83 | 1412 | 19 | 26% (−32% to 58%) |
| IIVc | 5001 | 1724 | 1412 | 242 | 48% (37%–57%) |
| aIIV | 5001 | 40 | 1412 | 3 | 76% (−8% to 95%) |
| By influenza type | |||||
| A(H1N1)pdm09 | 5001 | 1994 | 396 | 91 | 42% (23%–56%) |
| A(H3N2) | 5001 | 1994 | 694 | 166 | 37% (21%–50%) |
| B | 5001 | 1994 | 190 | 15 | 71% (49%–84%) |
| Ages 65+ | |||||
| All vaccinated | 420 | 1537 | 61 | 180 | 30% (−6% to 54%) |
| By vaccine type | |||||
| aIIV | 420 | 1428 | 61 | 167 | 29% (−10% to 54%) |
| By influenza type | |||||
| A(H1N1)pdm09 | 420 | 1537 | 21 | 59 | 5% (−87% to 52%) |
| A(H3N2) | 420 | 1537 | 32 | 97 | 35% (−11% to 62%) |
| B | 420 | 1537 | < 3 | < 3 | Insufficient cases |
Abbreviations: CI = confidence interval, unvacc = unvaccinated, vacc = vaccinated.
a
Cell counts include those with missing data for onset and vaccination date.
b
Adjustments were made for week of sample (spline), age group, scheme and clinical risk status.