Background
Methods
Study population
Study design and statistical analysis
Results
Description of cases and controls
Laboratory confirmed influenza cases | Test-negative controls | ||
---|---|---|---|
n (%) | n (%) | p-value | |
Total
| 303 (100) | 286 (100) | |
Age groups (years)
| 0.004 | ||
< 5 | 10 (3.3) | 9 (3.1) | |
5 - 14 | 38 (12.4) | 19 (6.6) | |
15 - 44 | 174 (57.4) | 151 (52.8) | |
45 - 64 | 65 (21.5) | 69 (24.1) | |
65 - 79 | 13 (4.3) | 26 (9.1) | |
≥ 80 | 3 (1.0) | 12 (4.2) | |
Sex
| 0.387 | ||
Male | 146 (48.2) | 148 (51.7) | |
Female | 157 (51.8) | 138 (48.3) | |
Residence
| 0.943 | ||
Rural | 43 (14.2) | 40 (14.0) | |
Urban | 260 (85.9) | 246 (86.0) | |
Major chronic conditions
| 0.005 | ||
0 | 232 (76.5) | 199 (69.6) | |
1 | 59 (19.5) | 56 (19.6) | |
> 1 | 12 (4.0) | 31 (10.8) | |
Outpatient visits in the previous year
| 0.047 | ||
0 | 53 (17.5) | 33 (11.5) | |
1 to 4 | 134 (44.2) | 120 (42.0) | |
> 4 | 116 (38.3) | 133 (46.5) | |
Health care setting
| <0.001 | ||
Primary health care | 290 (95.7) | 240 (83.9) | |
Hospital | 13 (4.3) | 46 (16.1) | |
Period
| <0.001 | ||
Week 43 to 46/2010 | 5 (1.7) | 40 (14.0) | |
Week 47 to 50/2010 | 6 (1.9) | 18 (6.3) | |
Week 51/2010 to 2/2011 | 192 (63.4) | 101 (35.3) | |
Week 3 to 6/2011 | 81 (26.7) | 95 (33.2) | |
Week 7 to 12/2011 | 19 (6.3) | 32 (11.2) | |
Delay between symptom onset and swabbing
| 0.118 | ||
≤4 days | 297 (98.0) | 274 (95.8) | |
>4 days | 6 (2.0) | 12 (4.2) | |
Pandemic influenza vaccine 2009-2010
| 0.001 | ||
No | 297 (98.0) | 260 (90.9) | |
Yes | 6 (2.0) | 26 (9.1) | |
Seasonal influenza vaccine 2010-2011
| <0.001 | ||
No | 290 (95.7) | 241 (84.3) | |
Yes | 13 (4.3) | 45 (15.7) |
Effectiveness of the 2010–2011 seasonal influenza vaccine
Cases/controls | Crude vaccine effectiveness, % (95% CI) | p-value | Adjusted vaccine effectiveness, % (95% CI) | p-value | |
---|---|---|---|---|---|
All swabbed patients
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 297/260 | Ref. | Ref. | ||
Yes | 6/26 | 80 (50; 92) | <0.001 | 45 (−68; 82)
a
| 0.297 |
Seasonal vaccine 2010-2011 | |||||
No | 290/241 | Ref. | Ref. | ||
Yes | 13/45 | 76 (54; 87) | <0.001 | 67 (24; 86)
a
| 0.009 |
Patients swabbed within 4 days of symptom onset
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 292/250 | Ref. | Ref. | ||
Yes | 6/25 | 79 (49; 92) | 0.001 | 44 (−71; 82)
a
| 0.309 |
Seasonal vaccine 2010-2011 | |||||
No | 286/235 | Ref. | Ref. | ||
Yes | 12/40 | 75 (52; 87) | <0.001 | 65 (16; 85)
a
| 0.018 |
Influenza A(H1N1)pdm09 cases vs. controls
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 262/260 | Ref. | Ref. | ||
Yes | 5/26 | 81 (49; 93) | <0.001 | 60 (−30; 87)
a
| 0.129 |
Seasonal vaccine 2010-2011 | |||||
No | 254/241 | Ref. | Ref. | ||
Yes | 13/45 | 73 (48; 86) | <0.001 | 61 (9; 83)
a
| 0.030 |
Influenza B cases vs. controls
| |||||
Seasonal vaccine 2010-2011 | |||||
No | 33/241 | Ref. | Ref. | ||
Yes | 0/45 | 89 (33; 100)c
| 0.010 | 93 (36; 100) c,d
| 0.017 |
Subjects with indication for seasonal vaccination
b
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 82/85 | Ref. | Ref. | ||
Yes | 6/21 | 70 (24; 89) | 0.013 | 28 (−147; 79)
a
| 0.599 |
Seasonal vaccine 2010-2011 | |||||
No | 76/69 | Ref. | Ref. | ||
Yes | 12/37 | 71 (39; 86) | 0.001 | 64 (8; 86)
a
| 0.034 |
Primary health care patients
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 286/227 | Ref. | Ref. | ||
Yes | 4/13 | 76 (24; 92) | 0.015 | 56 (−70; 89)
e
| 0.231 |
Seasonal vaccine 2010-2011 | |||||
No | 280/216 | Ref. | Ref. | ||
Yes | 10/24 | 68 (31; 75) | 0.003 | 68 (17; 87)
e
| 0.019 |
Hospitalized patients
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 11/33 | Ref. | Ref. | ||
Yes | 2/13 | 54 (−137; 91) c
| 0.355 | 8 (−967; 94) c,e
| 1.000 |
Seasonal vaccine 2010-2011 | |||||
No | 10/25 | Ref. | Ref. | ||
Yes | 3/21 | 64 (−47; 91) c
| 0.154 | 61 (−316; 98) c,e
| 0.677 |
Subjects aged less than 50 years
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 246/191 | Ref. | Ref. | ||
Yes | 2/6 | 74 (−30; 95) | 0.100 | 60 (−65; 94)
a
| 0.341 |
Seasonal vaccine 2010-2011 | |||||
No | 245/188 | Ref. | Ref. | ||
Yes | 3/9 | 75 (4; 93) | 0.043 | 73 (−21; 94)
a
| 0.086 |
Subjects aged 50 years or older
| |||||
Pandemic vaccine 2009-2010 | |||||
No | 51/69 | Ref. | Ref. | ||
Yes | 4/20 | 73 (26; 91) | 0.024 | 47 (−133; 88)
a
| 0.401 |
Seasonal vaccine 2010-2011 | |||||
No | 45/53 | Ref. | Ref. | ||
Yes | 10/36 | 67 (27; 85) | 0.007 | 69 (0; 91)
a
| 0.050 |
Effect of the monovalent A(H1N1)pdm09 vaccine received in the previous season
Case/control | Crude vaccine effectiveness, % (95% CI) a
| P-value | Adjusted vaccine effectiveness, % (95% CI) b
| P-value | |
---|---|---|---|---|---|
All swabbed patients
| |||||
Seasonal and pandemic vaccines | 2 / 19 | 91 (63; 98) | 0.001 | 87 (30; 98) | 0.017 |
Only seasonal vaccine | 11 / 26 | 65 (28; 83) | 0.004 | 64 (14; 85) | 0.022 |
Only pandemic vaccine | 4 / 7 | 53 (−62; 86) | 0.230 | 21 (−252; 82) | 0.755 |
Unvaccinated | 286 / 234 | Ref. | Ref. | ||
Influenza A(H1N1)pdm09 cases vs. controls
| |||||
Seasonal and pandemic vaccines | 2 / 19 | 91 (57; 98) | 0.002 | 86 (25; 97) | 0.022 |
Only seasonal vaccine | 11 / 26 | 61 (18; 81) | 0.012 | 60 (2; 83) | 0.044 |
Only pandemic vaccine | 3 / 7 | 60 (−56; 90) | 0.187 | 53 (−132; 91) | 0.351 |
Unvaccinated | 251 / 234 | Ref. | Ref. | ||
Subjects with indication for seasonal vaccination
| |||||
Seasonal and pandemic vaccines | 2 / 16 | 89 (50; 97) | 0.004 | 81 (−9; 97) | 0.062 |
Only seasonal vaccine | 10 / 21 | 58 (3; 81) | 0.041 | 50 (−38; 82) | 0.179 |
Only pandemic vaccine | 4 / 5 | 29 (−176; 82) | 0.623 | −32 (−694; 78) | 0.763 |
Unvaccinated | 72 / 64 | Ref. | Ref. |