TABLE 2. Number and percentage outpatients with acute respiratory illness and cough (N = 3,254) receiving 2018–19 seasonal influenza vaccine, by influenza test result status, age group, and vaccine effectiveness* against all influenza A and B and against virus type A(H1N1)pdm09 — U.S. Influenza Vaccine Effectiveness Network, November 23, 2018–February 2, 2019.
| Influenza type/Age group | Influenza-positive |
Influenza-negative |
Vaccine effectiveness* |
|||
|---|---|---|---|---|---|---|
| Total | Vaccinated no. (%) | Total | Vaccinated no. (%) | Unadjusted % (95% CI) | Adjusted % (95% CI)† | |
|
Influenza A and B
| ||||||
| Overall |
465 |
198 (43) |
2,789 |
1,591 (57) |
44 (32 to 54) |
47 (34 to 57)§ |
| Age group | ||||||
| 6 mos–17 yrs |
173 |
58 (34) |
926 |
515 (56) |
60 (43 to 71) |
61 (44 to 73)§ |
| 18–49 yrs |
166 |
58 (35) |
932 |
403 (43) |
30 (1 to 50) |
37 (9 to 56)§ |
| ≥50 yrs |
126 |
82 (65) |
931 |
673 (72) |
29 (-6 to 52) |
24 (-15 to 51) |
|
Influenza A(H3N2)
| ||||||
| Overall |
101 |
42 (42) |
2,789 |
1,591 (57) |
46 (20 to 64) |
44 (13 to 64)§ |
|
Influenza A(H1N1)pdm09
| ||||||
| Overall |
293 |
125 (43) |
2,789 |
1,591 (57) |
44 (29 to 56) |
46 (30 to 58)§ |
| Age group | ||||||
| 6 mos–17 yrs |
106 |
37 (35) |
926 |
515 (56) |
57 (35 to 72) |
62 (40 to 75)§ |
| 18–49 yrs |
113 |
38 (34) |
932 |
403 (43) |
33 (0 to 56) |
45 (14 to 64)§ |
| ≥50 yrs | 74 | 50 (68) | 931 | 673 (72) | 20 (-33 to 52) | 8 (-59 to 46) |
* Vaccine effectiveness was estimated as 100% x (1 - odds ratio [ratio of odds of being vaccinated among outpatients with influenza-positive test results to the odds of being vaccinated among outpatients with influenza-negative test results]); odds ratios were estimated using logistic regression.
† Adjusted for study site, age group, sex, race/ethnicity, self-rated general health, number of days from illness onset to enrollment, and month of illness (4-week intervals) using logistic regression.
§ Statistically significant at p<0.05.