Table 3:
Indirect effectiveness of vaccination with trivalent inactivated influenza vaccine for the prevention of laboratory-confirmed influenza
| Year 1 (2009–10) | Year 2 (2010–11) | Year 3 (2011–12) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n/N (%) | Mean vaccine efficacy (95% CI) | p value | n/N (%) | Mean vaccine efficacy (95% CI) | p value | n/N (%) | Mean vaccine efficacy (95% CI) | p value | ||||
| IIV3 | IPV | IIV3 | IPV | IIV3 | IPV | |||||||
| Any influenza infection | 214/3949 (5%) |
218/3966 (5%) |
1·7% (−18·8 to 18·6) | 0·86 | 150/4246 (4%) |
175/4230 (4%) |
14·9% (−5·8 to 31·6) |
0·15 | 39/4323 (1%) |
60/4121 (1%) |
38·1% (7·4 to 58·6) |
0·020 |
| Sex | ||||||||||||
| Female | 128/1959 (7%) |
136/2005 (7%) |
2·6% (−24·0 to 23·5) | 0·83 | 88/2106 (4%) |
99/2125 (5%) |
10·1% (−19·8 to 32·6) |
0·47 | 24/2118 (1%) |
41/2064 (2%) |
35·9% (−4·3 to 60·5) |
0·073 |
| Male | 86/1990 (4%) |
82/1961 (4%) |
−17 (−37·6 to 24·9) | 0·91 | 62/2140 (3%) |
76/2105 (4%) |
20·5% (−11·2 to 43·2) |
0·18 | 12/2205 (1%) |
19/2057 (1%) |
41·2% (−21·2 to 71·4) |
0·15 |
| Age group | ||||||||||||
| <6 months | 12/151 (8%) |
23/183 (13%) |
43·3% (−14·0 to 71·8) | 0·11 | 17/167 (10%) |
23/233 (10%) |
7·8% (−72·6 to 50·7) |
0·80 | 2/110 (2%) |
3/131 (2%) |
17·5% (−393·7 to 86·2) |
0·83 |
| 6 months to 10 years | 9/58 (16%) |
4/77 (5%) |
−204·9% (−890·3 to 6·1) | 0·064 | 1/45 (2%) |
6/65 (9%) |
77·2% (−89·5 to 97·3) |
0·17 | 2/45 (4%) |
1/62 (2%) |
−184·7% (−3040·0 to 74·2) | 0·39 |
| 11–17 years | 57/631 (9%) |
42/548 (8%) |
−19·2% (−77·5 to 20·0) | 0·39 | 22/681 (3%) |
25/573 (4%4) |
25·6% (−31·9 to 58·1) |
0·31 | 16/642 (2%) |
14/606 (2%) |
−8·3% (−121·8 to 47·2) |
0·83 |
| 18–49 years | 116/2448 (5%) |
120/2469 (5%) |
1·8% (−26·8 to 23·9) | 0·89 | 67/2612 (3%) |
90/2645 (3%) |
24·3% (−3·8 to 44·8) |
0·084 | 17/2736 (1%) |
31/2627 (1%) |
47·3% (4·8 to 70·8) |
0·034 |
| 50–64 years | 15/446 (3%) |
21/447 (5%) |
29·5% (−36·7 to 63·7) | 0·30 | 30/499 (6%) |
19/460 (4%) |
−47·2% (−161·6 to 17·1) |
0·19 | 2/542 (<1%) |
7/454 (2%) |
76·2% (−14·7 to 95·0) |
0·074 |
| ≥65 years | 5/215 (2%) |
8/242 (3%) |
30·4% (−112·9 to 77·2) | 0·52 | 13/242 (5%) |
12/254 (5%) |
−16·5% (−155·3 to 46·8) |
0·70 | 0/248 | 4/241 (2%) |
NA | ‥ |
| Influenza A (H1N1) pdm09 | 113/3951 (3%) |
115/3970 (3%) |
1·4% (−27·8 to 24·0) | 0·91 | 5/4246 (<1%) |
0/4230 | NA | ‥ | 4/4323 (<1%) |
5/4121 (<1%) |
23·9% (−183·6 to 79·6) |
0·69 |
| Influenza A (H3N2) | 5/3975 (<1%) |
2/4001 (<1%) |
−151·2% (−1194·6 to 51·3) |
0·27 | 118/4246 (3%) |
128/4230 (3) |
8·4% (−17·6 to 28·7) |
0·49 | 0/4323 | 0/4121 | NA | ‥ |
| Influenza B | 104/3973 (3%) |
112/3997 (3%) |
6·7% (−21·9 to 28·6) | 0·61 | 31/4246 (1%) |
48/4230 (1%) |
36·2% (−0·23 to 59·4) |
0·051 | 35/4323 (<1%) |
55/4121 (1%) |
39·4% (7·4 to 60·3) |
0·021 |
IIV3=trivalent inactivated influenza vaccine. IPV=inactivated poliovirus vaccine. NA=not applicable (ie, not possible to calculate vaccine efficacy in our model if one trial group has zero cases).