TABLE 2.
Clinical characteristics of study patients by influenza infection and vaccination status
| Controls - non influenza pneumonia (n=2605) |
Cases – influenza pneumonia (n=162) |
P value | Non-vaccinated (n=1973) |
Vaccinated (n=794) |
P value | |
|---|---|---|---|---|---|---|
| Comorbidities and risk factors | ||||||
| Need oxygen supplementation at home, % (n) | 7% (190) | 6% (10) | 0.59 | 5% (96) | 13% (104) | <0.001 |
| Adult BMI (kg/m2), median (IQR) | 27.4 (23.0, 33.0) | 27.9 (25.1, 34.7) | 0.08 | 27.4 (23.1, 32.9) | 27.7 (23.0, 33.4) | 0.76 |
| Children BMI categories | 1.00 | 0.84 | ||||
| Underweight | 20% (149) | 20% (8) | 19% (115) | 20% (42) | ||
| Normal | 55% (419) | 54% (22) | 55% (324) | 56% (117) | ||
| Overweight | 11% (85) | 12% (5) | 11% (65) | 12% (25) | ||
| Obese | 14% (108) | 15% (6) | 15% (88) | 12% (26) | ||
| Smoking, % (n) | 0.007 | <0.001 | ||||
| Non-smoking | 68% (1773) | 61% (99) | 68% (1346) | 66% (526) | ||
| Current smoking | 14% (374) | 23% (38) | 17% (327) | 11% (85) | ||
| Past smoking | 18% (458) | 15% (25) | 15% (300) | 23% (183) | ||
| Unknown | 4% (99) | 6% (10) | 4% (85) | 3% (24) | ||
| Chronic conditions | 62% (1628) | 56% (91) | 0.11 | 59% (1159) | 71% (560) | <0.001 |
| Asthma or Reactive Airway Disease | 33% (852) | 33% (53) | 1.00 | 32% (635) | 34% (270) | 0.36 |
| Chronic Obstructive Pulmonary Disease (COPD) | 11% (292) | 11% (18) | 0.97 | 9% (170) | 18% (140) | <0.001 |
| Congenital Heart Disease | 3% (87) | 0% (0) | 0.02 | 3% (51) | 5% (36) | 0.008 |
| Coronary Artery Disease | 14% (358) | 15% (24) | 0.70 | 11% (211) | 22% (171) | <0.001 |
| Heart failure | 11% (279) | 5% (8) | 0.02 | 7% (145) | 18% (142) | <0.001 |
| Diabetes mellitus | 13% (337) | 12% (19) | 0.66 | 12% (227) | 16% (129) | <0.001 |
| Blood Disorder (e.g. sickle cell disease) | 7% (189) | 5% (8) | 0.27 | 6% (120) | 10% (77) | <0.001 |
| Chronic Kidney Disease | 8% (221) | 6% (9) | 0.19 | 6% (125) | 13% (105) | <0.001 |
| Chronic Liver Disease | 3% (82) | 6% (9) | 0.10 | 3% (60) | 4% (31) | 0.25 |
| Splenectomy | 1% (31) | 0% (0) | 0.16 | 1% (16) | 2% (15) | 0.02 |
| Non-cancer immunosuppressive condition | 9% (236) | 11% (18) | 0.38 | 7% (134) | 13% (106) | <0.001 |
| HIV | 2% (43) | 4% (6) | 0.06 | 1% (25) | 3% (24) | <0.002 |
| Cancer | 9% (230) | 8% (13) | 0.73 | 7% (131) | 14% (112) | <0.001 |
| Immunosuppression | 15% (393) | 17% (28) | 0.45 | 7% (142) | 14% (112) | <0.001 |
| Seizure disorder | 5% (137) | 6% 10) | 0.62 | 5% (95) | 7% (52) | 0.07 |
| Obstructive Sleep Apnea | 3% (86) | 2% (3) | 0.31 | 2% (45) | 6% (44) | <0.001 |
| Cerebral Palsy | 1% (35) | 2% (3) | 0.59 | 1% (22) | 2% (16) | 0.07 |
| Dementia | 1% (24) | 1% (1) | 0.69 | 1% (14) | 1% (11) | 0.09 |
| Stroke | 3% (72) | 1% (2) | 0.24 | 2% (45) | 4% (29) | 0.04 |
| Guillain-Barre Syndrome | 0% (4) | 1% (1) | 0.18 | 0% (2) | 0% (3) | 0.12 |
| Scoliosis | 1% (14) | 1% (1) | 0.89 | 1% (10) | 1% (5) | 0.69 |
| Down’s Syndrome | 1% (38) | 0% (0) | 0.12 | 1% (18) | 3% (20) | <0.001 |
| Other Chromosomal Abnormality | 1% (36) | 1% (2) | 0.88 | 1% (23) | 2% (15) | 0.14 |
| Currently on steroids | 11% (289) | 11% (18) | 1.00 | 10% (192) | 14% (115) | <0.001 |
| Influenza and vaccination status, and timing of admission | ||||||
| Verified influenza vaccination, % (n) | 29% (766) | 17% (28) | 0.002 | 0% | 100% | − |
| Influenza confirmed by RT-PCR, % (n) | 0% | 100% | − | 7% (134) | 4% (28) | <0.001 |
| Disease onset to admission, median days (IQR) | 3 (2,7) | 3 (2, 6) | 0.78 | 3 (2, 7) | 3 (2, 6) | 0.51 |
| Admission week in flu season, median (IQR) | 20.0 (13.0, 31.0) | 26.0 (18.0, 32.8) | <0.001 | 18 (11, 29) | 27 (19, 35) | <0.001 |
| Days from vaccination to admission, median (IQR) | 108.5 (64.0, 163.0) | 124.0 (90.2, 150.2) | 0.52 | 109.5 (64.2, 162.8) | ||
| Days from season start to admission, median (IQR) | 138 (84, 214) | 180 (124, 224) | <0.001 | 124 (76, 198) | 184 (127, 240) | <0.001 |
Footnote: Immunosuppression included non-cancer immunosuppressive conditions, cancer (other than skin cancer) and HIV infection with CD4 count ≥200/mm3; chronic conditions encompass medical conditions associated with influenza-associated complications including cardiopulmonary disease, diabetes mellitus, blood disorders, chronic liver/kidney disease, immunosuppressive conditions (including cancer), and neuromuscular diseases. BMI categories for children were determined per CDC guidelines: Underweight (<5th BMI-for-age percentile), Normal (5th – <85th percentile), Overweight (85th – <95th percentile), and Obese (>=95th percentile). Additional information on the characteristics of the study population is available in supplementary tables 2S and 3S.