Table 2.
Risk of severe influenza outcomes among individuals hospitalised with laboratory-confirmed influenza, by influenza vaccination status
|
Children aged 6–24 months |
Adults aged 18–64 years with pre-existing medical conditions |
Older adults aged ≥65 years |
|||||
|---|---|---|---|---|---|---|---|
| Unvaccinated (n=386) | Partially vaccinated (n=193) | Fully vaccinated (n=70) | Unvaccinated (n=402) | Vaccinated (n=118) | Unvaccinated (n=969) | Vaccinated (n=609) | |
| Length of hospital stay, days | |||||||
| Median (IQR) | 5 (3–8) | 5 (3–9) | 5 (3–8) | 8 (4–15) | 7 (4–11) | 7 (4–13) | 7 (4–11) |
| HR (95% CI) | 1 (ref) | 1·15 (1·03–1·30)* | 1·25 (1·05–1·48)* | 1 (ref) | 1·31 (0·89–1·92) | 1 (ref) | 0·84 (0·67–1·05) |
| aHR (95% CI) | 1 (ref) | 1·14 (1·01–1·29)* | 1·24 (1·04–1·47)* | 1 (ref) | 1·78 (1·18–2·69)* | 1 (ref) | 0·82 (0·65–1·04) |
| Length of stay >5 days | |||||||
| n (%) | 158 (40·9%) | 88 (45·6%) | 30 (42·9%) | 261 (64·9%) | 76 (64·4%) | 620 (64·0%) | 375 (61·6%) |
| OR (95% CI) | 1 (ref) | 1·15 (0·80–1·63) | 1·05 (0·63–1·78) | 1 (ref) | 0·98 (0·64–1·50) | 1 (ref) | 0·90 (0·73–1·11) |
| aOR (95% CI) | 1 (ref) | 0·98 (0·76–1·25) | 0·79 (0·55–1·14) | 1 (ref) | 0·69 (0·53–0·90)* | 1 (ref) | 0·67 (0·57–0·79)* |
| ICU admission | |||||||
| n (%) | 57 (14·8%) | 24 (12·4%) | 6 (8·6%) | 111 (27·6%) | 28 (23·7%) | 167 (17·2%) | 104 (17·1%) |
| OR (95% CI) | 1 (ref) | 0·82 (0·49–1·37) | 0·54 (0·22–1·31) | 1 (ref) | 0·82 (0·51–1·31) | 1 (ref) | 0·99 (0·76–1·29) |
| aOR (95% CI) | 1 (ref) | 0·64 (0·44–0·92)* | 0·52 (0·28–0·98)* | 1 (ref) | 1·25 (0·93–1·67) | 1 (ref) | 0·88 (0·72–1·08) |
| In-hospital death | |||||||
| n (%) | 8 (2·1%) | 3 (1·6%) | 1 (1·4%) | 45 (11·2%) | 10 (8·5%) | 163 (16·8%) | 57 (9·3%)† |
| OR (95% CI) | 1 (ref) | 0·75 (0·19–2·85) | 0·68 (0·08–5·58) | 1 (ref) | 0·73 (0·36–1·51) | 1 (ref) | 0·51 (0·37–0·70)* |
| aOR (95% CI) | 1 (ref) | 1·35 (0·57–3·20) | 0·88 (0·16–4·82) | 1 (ref) | 1·09 (0·73–1·63) | 1 (ref) | 0·62 (0·50–0·78)* |
| ICU admission and discharge | |||||||
| n (%) | 49 (12·7%) | 21 (10·9%) | 5 (7·1%) | 82 (20·4%) | 22 (18·6%) | 100 (10·3%) | 78 (12·8%) |
| OR (95% CI) | 1 (ref) | 0·83 (0·48–1·44) | 0·52 (0·20–1·37) | 1 (ref) | 0·87 (0·51–1·47) | 1 (ref) | 1·24 (0·90–1·70) |
| aOR (95% CI) | 1 (ref) | 0·56 (0·38–0·84)* | 0·50 (0·25–0·97)* | 1 (ref) | 1·20 (0·86–1·68) | 1 (ref) | 1·33 (0·93–1·51) |
| No ICU admission and in-hospital death | |||||||
| n (%) | 0 (0%) | 0 (0%) | 0 (0%) | 16 (4·0%) | 4 (3·4%) | 96 (9·9%) | 31 (5·1%)† |
| OR (95% CI) | NE (ref) | NE | NE | 1 (ref) | 0·83 (0·27–2·53) | 1 (ref) | 0·47 (0·31–0·72)* |
| aOR (95% CI) | NE (ref) | NE | NE | 1 (ref) | 1·41 (0·48–1·87) | 1 (ref) | 0·73 (0·55–0·96)* |
| ICU admission and in-hospital death | |||||||
| n (%) | 8 (2·1%) | 3 (1·6%) | 1 (1·4%) | 29 (7·2%) | 6 (5·1%) | 67 (6·9%) | 26 (4·3%)‡ |
| OR (95% CI) | 1 (ref) | 0·75 (0·19–2·85) | 0·68 (0·08–5·58) | 1 (ref) | 0·69 (0·28–1·71) | 1 (ref) | 0·60 (0·38–0·95)* |
| aOR (95% CI) | 1 (ref) | 1·35 (0·57–3·21) | 0·88 (0·16–4·83) | 1 (ref) | 1·21 (0·73–2·01) | 1 (ref) | 0·46 (0·33–0·64)* |
HRs were computed using Cox regression models with competing risk of death, weighted by inverse probability of treatment weights, and adjusted by antiviral use, duration of illness before admission, and calendar week (fit as a cubic spline). Values >1 indicate earlier discharge for vaccinated individuals compared to unvaccinated. To calculate aORs, logistic regression models were weighted by inverse probability treatment weights and adjusted for antiviral medication use, duration of illness at admission, and calendar week (fit as a cubic spline); pooled ORs were calculated using the pool() function in R, which averages the estimates across the 20 imputed datasets and calculates total variance across the repeated analyses using Rubin's rule. HR=hazard ratio. aHR=adjusted hazard ratio. OR=odds ratio. aOR=adjusted odds ratio. NE=not estimated (insufficient data).
95% CI does not overlap with 1 (significant difference compared with reference category).
Significant at p<0·001 based on χ2 test for comparisons.
Significant at p<0·05 based on χ2 test for comparisons.