Table 2.
Adjusted Vaccine Effectiveness Against Influenza-Associated Illness Among Patients Aged ≥6 Monthsa
| Virus by Patient Age | No. Vaccinated/Total No. (% Vaccinated) | VE (95% CI), % | |
|---|---|---|---|
| Influenza-Positive (Case Patients) | Influenza Negative (Noncase Patients) | ||
| All influenza viruses | |||
| All ages | 1316/2763 (48) | 4065/7249 (56) | 29 (21–35) |
| 6 mo to 8 y | 301/751 (40) | 977/1677 (58) | 48 (37–58) |
| 9–17 y | 217/489 (44) | 319/772 (41) | 7 (−20 to 28) |
| 18–49 y | 320/821 (39) | 1077/2435 (44) | 25 (10–37) |
| 50–64 y | 266/442 (60) | 829/1324 (63) | 14 (−10 to 33) |
| ≥65 y | 212/260 (82) | 863/1041 (83) | 12 (−31 to 40) |
| A(H1N1)pdm09 | |||
| All ages | 563/1325 (42) | 4065/7249 (56) | 44 (37–51) |
| 6 mo to 8 y | 128/389 (33) | 977/1677 (58) | 59 (47–69) |
| 9–17 y | 47/115 (41) | 319/772 (41) | 24 (−18 to 51) |
| 18–49 y | 150/442 (34) | 1077/2435 (44) | 43 (28–55) |
| 50–64 y | 138/255 (54) | 829/1324 (63) | 30 (6–48) |
| ≥65 y | 100/124 (81) | 863/1041 (83) | 16 (−41 to 51) |
| All influenza A(H3N2) virusesb | |||
| All ages | 709/1350 (53) | 4065/7249 (56) | 9 (−4 to 20) |
| 6 mo to 8 y | 163/335 (49) | 977/1677 (58) | 24 (1–42) |
| 9–17 y | 162/355 (46) | 319/772 (41) | 3 (−30 to 28) |
| 18–49 y | 154/351 (44) | 1077/2435 (44) | 3 (−25 to 24) |
| 50–64 y | 121/176 (69) | 829/1324 (63) | −20 (−74 to 18) |
| ≥65 y | 109/133 (82) | 863/1041 (83) | 13 (−46 to 48) |
| A(H3N2) genetic group 3C.3a | |||
| All ages | 520/977 (53) | 4065/7249 (56) | 5 (−10 to 19) |
| 6 mo to 8 y | 132/270 (49) | 977/1677 (58) | 23 (−3 to 43) |
| 9–17 y | 128/276 (46) | 319/772 (41) | 7 (−28 to 33) |
| 18–49 y | 117/246 (48) | 1077/2435 (44) | −10 (−47 to 18) |
| 50–64 y | 76/103 (74) | 829/1324 (63) | −48 (−142 to 10) |
| ≥65 y | 67/82 (82) | 863/1041 (83) | 20 (−52 to 58) |
| A(H3N2) genetic group 3C.2a1 | |||
| All ages | 37/74 (50) | 4065/7249 (56) | 46 (11–68) |
| Influenza B | |||
| All ages | 31/64 (48) | 4065/7249 (56) | 34 (−12 to 62) |
Abbreviations: CI, confidence interval; VE, vaccine effectiveness.
aVE against influenza-associated illness in the ambulatory care setting among patients enrolled in the US Influenza Vaccine Effectiveness Network from 23 November 2018 through 3 May. VE was estimated as 100 × (1 − OR), where OR is the odds ratio for influenza among vaccinated compared with unvaccinated persons. ORs were estimated using logistic regression. If the 95% CI excludes 0, the results are considered statistically significant. Models adjusted study site, sex, age, race/ethnicity, self-reported general health status, interval from illness onset to study enrollment, and calendar time (biweekly interval).
bIncludes influenza A(H3N2) viruses for which genetic group was not determined.