Effect of influenza vaccination in the current and 5 previous seasons in preventing influenza among patients with asthma, by age group and subtype
| Analysis subset | No. (%) of patients with confirmed influenza | No. (%) of influenza-negative patients | Crude OR (95% CI) | Adjusted OR (95% CI)* | Vaccination effect, % (95% CI) |
|---|---|---|---|---|---|
| Aged 9–64 yr | |||||
| Total | 240 (100) | 239 (100) | |||
| Current-season vaccination | 52 (21.7) | 92 (38.4) | 0.40 (0.27 to 0.61) | 0.45 (0.28 to 0.72)¶ | 55 (38 to 72) |
| Vaccination in previous seasons only | 25 (10.4) | 31 (55.4) | 0.57 (0.32 to 1.02) | 0.69 (0.36 to 1.32) ¶ | 31 (−32 to 64) |
| Never vaccinated | 163 (67.9) | 116 (41.6) | Ref. | Ref. | Ref. |
| Aged ≥ 65 yr | |||||
| Total | 181 (100) | 372 (100) | |||
| Current-season vaccination | 127 (70.2) | 261 (70.2) | 0.75 (0.44 to 1.28) | 0.67 (0.37 to 1.21) ¶ | 33 (−21 to 63) |
| Vaccination in previous seasons only | 28 (15.5) | 71 (18.1) | 0.61 (0.31 to 1.17) | 0.61 (0.30 to 1.25) ¶ | 39 (−25 to 70) |
| Never vaccinated | 26 (14.4) | 40 (10.8) | Ref. | Ref. | Ref. |
| A/H1N1 subtype† | |||||
| Total | 155 (100) | 517 (100) | |||
| Current-season vaccination | 54 (34.8) | 305 (59.0) | 0.28 (0.19 to 0.42) | 0.48 (0.28 to 0.80) | 52 (20 to 72) |
| Vaccination in previous seasons only | 17 (11.0) | 79 (15.3) | 0.34 (0.19 to 0.62) | 0.65 (0.32 to 1.33) | 35 (−33 to 68) |
| Never vaccinated | 84 (54.2) | 133 (25.7) | Ref. | Ref. | Ref. |
| A/H3N2 subtype‡ | |||||
| Total | 147 (100) | 464 (100) | |||
| Current-season vaccination | 74 (50.3) | 263 (56.7) | 0.65 (0.43 to 0.98) | 0.73 (0.43 to 1.22) | 27 (−22 to 57) |
| Vaccination in previous seasons only | 21 (14.3) | 81 (17.5) | 0.60 (0.34 to 1.07) | 0.65 (0.34 to 1.25) | 35 (−25 to 66) |
| Never vaccinated | 52 (35.4) | 120 (25.9) | Ref. | Ref. | Ref. |
| B type§ | |||||
| Total | 111 (100) | 364 (100) | |||
| Current-season vaccination | 47 (42.3) | 215 (59.1) | 0.44 (0.28 to 0.70) | 0.49 (0.26 to 0.91) | 51 (9 to 74) |
| Vaccination in previous seasons only | 14 (12.6) | 49 (13.5) | 0.57 (0.29 to 1.13) | 0.66 (0.29 to 1.49) | 34 (−49 to 71) |
| Never vaccinated | 50 (45.1) | 100 (27.5) | Ref. | Ref. | Ref. |
Note: CI = confidence interval, OR = odds ratio, Ref. = reference category. Current-season vaccination = vaccinated in the current season regardless of previous doses. We estimated the effect of influenza vaccination as (1 – adjusted OR) × 100.
↵* We adjusted ORs by age groups (9–64, 65–84 and ≥ 85 yr), other major chronic conditions, health care setting (primary health care or hospital), and month and season of sample collection.
↵† Pooled A/H1N1 analysis included 2015/16, 2017/18, 2018/19 and 2019/20 seasons.
↵‡ Pooled A/H3N2 analysis included 2015/16, 2016/17, 2017/18 and 2018/19 seasons.
↵§ Pooled B analysis included 2015/16, 2017/18 and 2019/20 seasons.
↵¶ There were no significant interactions between age group and current season vaccination (p = 0.3) or vaccination in previous seasons (p = 0.9).