Table 1.
Comparison of cases testing positive for any influenza virus and test-negative cases in Hong Kong, September 2012 to August 2017
| Characteristic | Influenza-positive (n=2500) N (%) |
Influenza-negative (n=13195) N (%) |
p-value a | ||
|---|---|---|---|---|---|
| Age group | |||||
| 6m-2y | 923 | (36.9%) | 6863 | (52.0%) | <0.001 |
| 3–5y | 834 | (33.4%) | 3637 | (27.6%) | |
| 6–17y | 743 | (29.7%) | 2695 | (20.4%) | |
| Female | 1135 | (45.4%) | 5745 | (43.5%) | 0.090 |
| Season | |||||
| 2012/13 | 142 | (5.7%) | 1610 | (12.2%) | <0.001 |
| 2013/14 | 194 | (7.8%) | 1040 | (7.9%) | |
| 2014/15 | 203 | (8.1%) | 1401 | (10.6%) | |
| 2015/16 | 1051 | (42.0%) | 4566 | (34.6%) | |
| 2016/17 | 910 | (36.4%) | 4578 | (34.7%) | |
| 3 Periods | |||||
| Sep - Dec | 283 | (11.3%) | 4526 | (34.3%) | <0.001 |
| Jan - Apr | 1521 | (60.8%) | 4649 | (35.2%) | |
| May - Aug | 696 | (27.8%) | 4020 | (30.5%) | |
| Receipt of influenza vaccination b | |||||
| Overall | 159 | (6.4%) | 1445 | (11.0%) | <0.001 |
| By age group | |||||
| 6 months – 2 years | 36 | (3.9%) | 514 | (7.5%) | <0.001 |
| 3 – 5 years | 65 | (7.8%) | 608 | (16.7%) | |
| 6 – 17 years | 58 | (7.8%) | 323 | (12.0%) | |
| By intervals since vaccination c | 154/159 | (96.9%) | 1368/1445 | (94.7%) | |
| .5 – 2 months | 16 | (10.4%) | 337 | (24.6%) | 0.001 |
| 3 – 4 months | 54 | (35.1%) | 377 | (27.6%) | |
| 5 – 6 months | 38 | (24.7%) | 336 | (24.6%) | |
| 7 – 9 months | 42 | (27.3%) | 279 | (20.4%) | |
| 10 – 12 months | 4 | (2.6%) | 39 | (2.9%) | |
a
p-values estimated by chi-squared tests or Fisher’s exact test whenever appropriate
b
Receipt of influenza vaccination defined as receipt of a quadrivalent or trivalent inactivated influenza vaccine with an age-appropriate schedule within 12 months prior admission and for current season.
c
A total of 82/1604 (5.1%) children were with missing vaccination time.