Table 2:
Total efficacy of any 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 | 151/1572 (10%) |
206/1633 (13%) |
25·6% (6·8 to 40·6) |
0·010 | 105/1705 (6%) |
182/1814 (10%) |
41·0% (24·1 to 54·1) |
<0·0001 | 20/1670 (1%) |
81/1786 (5%) |
74·2% (57·8 to 84·3) |
<0·0001 |
| Sex | ||||||||||||
| Female | 66/707 (9%) |
92/709 (13%) |
28·6% (1·0 to 48·5) |
0·043 | 47/767 (6%) |
79/821 (10%) |
39·0% (11·0 to 58·1) |
0·0104 | 12/782 (2%) |
35/816 (4%) |
64·6% (30·7 to 81·9) |
0·0024 |
| Male | 85/865 (10%) |
114/924 (12%) |
24·8% (−1·7 to 44·4) |
0·064 | 58/938 (6%) |
103/993 (10%) |
42·7% (19·2 to 59·4) |
0·0015 | 8/888 (1%) |
46/970 (5%) |
81·5% (60·3 to 91·3) |
<0·0001 |
| Age group | ||||||||||||
| 6–35 months | 44/367 (12%) |
52/374 (14%) |
13·0% (−31·6 to 42·5) |
0·51 | 39/410 (10%) |
65/427 (15%) |
39·3% (6·9 to 60·4) |
0·022 | 6/416 (1%) |
19/391 (5%) |
70·5% (24·2 to 88·5) |
0·011 |
| 36 months to 8 years | 82/897 (9%) |
119/969 (12%) |
27·3% (2·7 to 45·7) |
0·032 | 55/938 (6%) |
99/1068 (9%) |
40·1% (14·7 to 57·9) |
0·0045 | 10/897 (1%) |
47/1043 (5%) |
74·7% (48·9 to 87·5) |
0·0001 |
| 9–10 years | 25/308 (8%) |
35/290 (12%) |
35·7% (−8·5 to 61·9) |
0·098 | 11/357 (3%) |
18/319 (6%) |
46·2% (−13·9 to 74·6) |
0·11 | 4/357 (1%) |
15/352 (4%) |
74·1% (21·8 to 91·4) |
0·017 |
| Time after vaccination | ||||||||||||
| 0–5 months | 19/1572 (1%) |
30/1633 (2%) |
36·1% (−14·9 to 64·5) |
0·13 | 4/1707 (<1%) |
3/1814 (<1%) |
−41·9% (−534·0 to 68·2) |
0·65 | ‥ | ‥ | ‥ | ‥ |
| 6–11 months | 132/1545 (9%) |
176/1590 (11%) |
23·1% (1·6 to 39·9) |
0·037 | 101/1684 (6%) |
179/1803 (10%) |
42·1% (25·5 to 55·0) |
<0·0001 | ‥ | ‥ | ‥ | ‥ |
| Influenza A (H1N1) pdm09 | 68/1580 (4%) |
81/1642 (5%) |
14·5% (−20·4 to 39·3) |
0·37 | ‥ | ‥ | ‥ | ‥ | ‥ | ‥ | ‥ | ‥ |
| Influenza A (H3N2) | ‥ | ‥ | ‥ | ‥ | 41/1706 (2%) |
124/1817 (7%) |
64·5% (48·5 to 75·5) |
<0·0001 | ‥ | ‥ | ‥ | ‥ |
| Influenza B | 88/1608 (5%) |
137/1710 (8%) |
32·5% (11·3 to 48·6) |
0·0048 | 63/1705 (4%) |
68/1814 (5%) |
4·9% (−38·9 to 34·9) |
0·79 | 17/1670 (1%) |
80/1786 (4%) |
76·5% (59·4 to 86·4) |
<0·0001 |
IIV3=trivalent inactivated influenza vaccine. IPV=inactivated poliovirus vaccine.
*
Efficacy calculation included all children who received at least one dose of vaccine, irrespective of whether they were assigned to receive one or two doses; exclusions listed in figure 1