Table 2. Characteristics of the children aged 6 months to 15 years enrolled in influenza vaccine effectiveness study, Japan, November 2014 to March 2015 (n = 3,752).
| Characteristic | Any influenza (%) |
Influenza A (%) | Influenza B (%) | Influenza negative (%) | Difference between ‘any influenza’ and ‘influenza negative’ |
|
|---|---|---|---|---|---|---|
| Sex | Female | 799 (48) | 777 (48) | 22 (52) | 965 (46) | p = 0.4575a |
| Male | 876 (52) | 856 (52) | 20 (48) | 1,111 (54) | ||
| Total | 1,675 | 1,633 | 42 | 2,076 | ||
| Age | 6–11 mo | 47 (3) | 44 (3) | 3 (7) | 136 (7) | p < 0.001b |
| 1–2 y | 229 (14) | 224 (14) | 5 (12) | 738 (36) | ||
| 3–5 y | 410 (24) | 402 (25) | 8 (19) | 574 (28) | ||
| 6–12 y | 793 (47) | 772 (47) | 21 (50) | 519 (25) | ||
| 13–15 y | 196 (12) | 191 (12) | 5 (12) | 110 (5) | ||
| Total | 1,675 | 1,633 | 42 | 2,077 | ||
| Comorbidity | No | 1,343 (82) | 1,307 (82) | 36 (86) | 1,585 (79) | p = 0.0251a |
| Yes | 293 (18) | 287 (18) | 6 (14) | 418 (21) | ||
| Total | 1,636 | 1,594 | 42 | 2,003 | ||
| Area of Kanto regionc | North | 125 (7) | 121 (7) | 4 (10) | 170 (8) | p = 0.4007d |
| Middle | 781 (47) | 766 (47) | 15 (36) | 996 (48) | ||
| South | 769 (46) | 746 (46) | 23 (55) | 911 (44) | ||
| Total | 1,675 | 1,633 | 42 | 2,077 | ||
| Month of illness onset | Nov 2014 | 38 (2) | 38 (2) | 0 (0) | 93 (4) | p < 0.001e |
| Dec 2014 | 646 (39) | 644 (39) | 2 (5) | 699 (34) | ||
| Jan 2015 | 742 (44) | 737 (45) | 5 (12) | 614 (30) | ||
| Feb 2015 | 188 (11) | 175 (11) | 13 (31) | 385 (19) | ||
| Mar 2015 | 61 (4) | 39 (2) | 22 (52) | 286 (14) | ||
| Total | 1,645 | 1,633 | 42 | 2,077 | ||
| Clinic visit (hours after symptom onset) | < 12 h | 551 (34) | 541 (34) | 10 (24) | 602 (31) | p = 0.0348f |
| 12–48 h | 994 (61) | 968 (61) | 26 (63) | 1,114 (57) | ||
| > 48 h | 80 (5) | 75 (5) | 5 (12) | 251 (13) | ||
| Total | 1,625 | 1,584 | 41 | 1,967 | ||
| > 12 h | 1,074 | 1,043 | 31 | 1,365 | ||
| Received vaccine in 2014/15 season | No | 978 (58) | 952 (58) | 26 (62) | 930 (45) | p < 0.001a |
| Yes | 697 (42) | 681 (42) | 16 (38) | 1,147 (55) | ||
| Total | 1,675 | 1,633 | 42 | 2,077 | ||
| Vaccine doses received in 2014/15 season | None | 978 (59) | 952 (58) | 26 (63) | 930 (45) | p < 0.001g |
| One | 224 (13) | 220 (14) | 4 (10) | 336 (16) | ||
| Two | 464 (28) | 457 (28) | 11 (27) | 807 (39) | ||
| Total | 1,670 | 1,629 | 41 | 2,073 | ||
| Treatment with neuraminidase inhibitors | No | 45 (4) | 44 (4) | 1 (3) | 1,409 (98) | p < 0.001h |
| Yes | 1,231 (96) | 1,201 (96) | 30 (97) | 29 (2) | ||
| Total | 1,276 | 1,245 | 31 | 1,438 | ||
a Chi-squared test.
b Chi-squared test, Cramer's V = 0.3188.
c Area of Kanto region. North: Gunma Prefecture and Tochigi Prefecture; Middle: Saitama Prefecture and Tokyo Prefecture; South: Kanagawa Prefecture and Shizuoka Prefecture.
d Chi-squared test, Cramer's V = 0.0221.
e Chi-squared test, Cramer's V = 0.2367.
f Chi-squared test, comparing the number of patients who came to the clinic < 12 hours after the onset with the number who came later.
g Chi-squared test, Cramer's V = 0.1379.
h Chi-squared test, Cramer's V = 0.9453.