Preliminary Flu Vaccine Effectiveness (VE) Data for 2023-2024
Reference: Interim Estimates of 2023–24 Seasonal Influenza Vaccine Effectiveness — United States
Inclusion Dates by Network
Network
Network
Network
Dates
Dates
Dates
September 1–January 31, 2023
Dates
September 1–January 31, 2023
October 1, 2023– February 2, 2024
Dates
October 1, 2023– February 2, 2024
October 10, 2023–January 24, 2024
Dates
October 10, 2023–January 24, 2024
October 15, 2023–January 15, 2024
Dates
October 15, 2023–January 15, 2024
Flu Vaccine Effectiveness for Children
TABLE 1. Number and percentage of children (6 months to 17 years) receiving seasonal influenza vaccine and vaccine effectiveness* by influenza type and subtype†— three networks, United States, 2023–24 influenza season
| Network (Setting) | Influenza positive N vaccinated / Total (%) |
Influenza negative N vaccinated / Total (%) |
VE (95% CI)¶ |
|---|---|---|---|
| Any Influenza | |||
| NVSN** (Outpatient††) | 123/622 (20%) | 793/2577 (31%) | 59 (48–67) |
| US Flu VE (Outpatient) | 29/283 (10%) | 182/736 (25%) | 67 (48–80) |
| VISION (Outpatient) | 961/6068 (16%) | 4579/15274 (30%) | 60 (57–64) |
| NVSN (Inpatient) | 29/128 (23%) | 543/1321 (41%) | 61 (40–75) |
| VISION (Inpatient) | 21/113 (19%) | 299/921 (32%) | 52 (16–72) |
| Any Influenza A | |||
| NVSN (Outpatient) | 84/411 (20%) | 793/2577 (31%) | 55 (41–66) |
| US Flu VE (Outpatient) | 27/212 (13%) | 182/736 (25%) | 46 (15–67) |
| VISION (Outpatient) | 920/5524 (17%) | 4579/15274 (30%) | 59 (55–62) |
| NVSN (Inpatient) | 25/102 (25%) | 543/1321 (41%) | 56 (30–73) |
| VISION (Inpatient) | 21/105 (20%) | 299/921 (32%) | 46 (7–69) |
| Influenza A(H1N1)pdm09 | |||
| NVSN (Outpatient) | 61/298 (20%) | 793/2577 (31%) | 54 (37–66) |
| US Flu VE (Outpatient) | 11/120 (9%) | 182/736 (25%) | 61 (26–81) |
| NVSN (Inpatient) | 18/79 (23%) | 543/1321 (41%) | 60 (32–77) |
| Influenza A(H3N2) | |||
| NVSN (Outpatient) | 19/87 (22%) | 793/2577 (31%) | 55 (20–74) |
| US Flu VE (Outpatient) | 2/17 (12) | 182/736 (25%) | — |
| NVSN (Inpatient) | 4/10 (40%) | 543/1321 (41%) | — |
| Influenza B | |||
| NVSN (Outpatient) | 39/216 (18%) | 793/2577 (31%) | 64 (47–75) |
| US Flu VE (Outpatient) | 3/76 (4%) | 182/736 (25%) | 89 (70–97) |
| VISION (Outpatient) | 45/571 (8%) | 4579/15274 (30%) | 79 (71–85) |
| NVSN (Inpatient) | 4/27 (15%) | 543/1321 (41%) | — |
| VISION (Inpatient) | 0/10 (0%) | 299/921 (32%) | — |
* VE was estimated using the test-negative design comparing vaccination odds among persons who tested positive for influenza to vaccination odds among persons who tested negative for any influenza and SARS-CoV-2. Calculated as (1 − adjusted OR ) × 100%; ORs were estimated using logistic regression. Firth logistic regression was used for NVSN’s inpatient estimates.
†Subtype was not available for VISION
¶All networks adjusted for geographic region, age, calendar time. US Flu VE and VISION adjusted for sex and race/ethnicity. US Flu VE also adjusted for time since illness onset and self-reported health status. VE estimates with fewer than 50 cases or from models that did not converge are not presented and are represented with a “—”
**Patients enrolled as outpatients in NVSN may have progressed to a more acute level of care, and those data may not be reflected in this analysis.
††Outpatient is defined as outpatient clinics, urgent care, and emergency departments for NVSN and US Flu VE. Outpatient is defined as urgent care and emergency departments for VISION.
Flu Vaccine Effectiveness for Adults
TABLE 2. Number and percentage of adults (≥18 years) receiving seasonal influenza vaccine and vaccine effectiveness* by influenza type and subtype†— three networks, United States, 2023–24 influenza season
| Network (Setting) | Influenza positive N vaccinated / Total (%) |
Influenza negative N vaccinated / Total (%) |
VE (95% CI)¶ |
|---|---|---|---|
| All adults (aged ≥18 years) | |||
| Any Influenza | |||
| US Flu VE (Outpatient**) | 177/568 (31%) | 803/1807 (44%) | 33 (16–47) |
| VISION (Outpatient) | 4501/18385 (24%) | 21356/52657 (41%) | 49 (47 –51) |
| IVY (Inpatient) | 200/632 (32%) | 1517/3872 (39%) | 44 (32–54) |
| VISION (Inpatient) | 728/1839 (40%) | 7425/14168 (52%) | 41 (34–47) |
| Any Influenza A | |||
| US Flu VE (Outpatient) | 168/495 (34%) | 803/1807 (44%) | 27 (9–43) |
| VISION (Outpatient) | 4343/15896 (27%) | 21356/52657 (41%) | 46 (44–48) |
| IVY (Inpatient) | 80/264 (30%) | 1517/3872 (39%) | 42 (23–57) |
| VISION (Inpatient) | 713/1742 (41%) | 7425/14168 (52%) | 40 (33–47) |
| Influenza A(H1N1)pdm09 | |||
| US Flu VE (Outpatient) | 111/308 (36%) | 803/1807 (44%) | 25 (1–43) |
| IVY (Inpatient) | 58/209 (28%) | 1517/3872 (39%) | 50 (30–64) |
| Influenza A(H3N2) | |||
| US Flu VE (Outpatient) | 14/67 (21%) | 803/1807 (44%) | 54 (11–77) |
| IVY (Inpatient) | 18/45 (40%) | 1517/3872 (39%) | — |
| Influenza B | |||
| US Flu VE (Outpatient) | 9/76 (12%) | 803/1807 (44%) | 78 (57–90) |
| VISION (Outpatient) | 164/2530 (6%) | 21356/52657 (41%) | 78 (74–81) |
| IVY (Inpatient) | 5/21 (24%) | 1517/3872 (39%) | — |
| VISION (Inpatient) | 18/103 (17%) | 7425/14168 (52%) | 60 (30–77) |
| Adults (aged 18–64 years) | |||
| Any Influenza | |||
| US Flu VE (Outpatient) | 136/489 (29%) | 503/1368 (37%) | 25 (4–42) |
| VISION (Outpatient) | 2557/14698 (17%) | 9194/33086 (28%) | 52 (50–55) |
| IVY (Inpatient) | 87/383 (23%) | 579/1927 (30%) | 49 (33–61) |
| VISION (Inpatient) | 197/773 (25%) | 1367/4050 (34%) | 40 (28–50) |
| Any Influenza A | |||
| US Flu VE (Outpatient) | 128/417 (31%) | 503/1368 (37%) | 13 (-13–34) |
| VISION (Outpatient) | 2425/12294 (20%) | 9194/33086 (28%) | 49 (46–51) |
| IVY (Inpatient) | 37/156 (24%) | 579/1927 (30%) | 42 (13–61) |
| VISION (Inpatient) | 187/694 (27%) | 1367/4050 (34%) | 38 (24–48) |
| Influenza B | |||
| US Flu VE (Outpatient) | 8/75 (11%) | 503/1368 (37%) | 75 (50–89) |
| VISION (Outpatient) | 135/2433 (6%) | 9194/33086 (28%) | 79 (75–82) |
| IVY (Inpatient) | 2/16 (12%) | 579/1927 (30%) | — |
| VISION (Inpatient) | 13/83 (16%) | 1367/4050 (34%) | 50 (5–74) |
| Older adults (aged ≥65 years) | |||
| Any Influenza | |||
| US Flu VE (Outpatient) | 41/79 (52%) | 300/439 (68%) | 51 (14–72) |
| VISION (Outpatient) | 1944/3687 (53%) | 12162/19571 (62%) | 41 (36–45) |
| IVY (Inpatient) | 113/249 (45%) | 938/1945 (48%) | 42 (23–56) |
| VISION (Inpatient) | 531/1066 (50%) | 6058/10118 (60%) | 42 (34–50) |
| Any Influenza A | |||
| US Flu VE (Outpatient) | 40/78 (51%) | 300/439 (68%) | 52 (16–73) |
| VISION (Outpatient) | 1918/3602 (53%) | 12162/19571 (62%) | 40 (36–45) |
| IVY (Inpatient) | 43/108 (40%) | 938/1945 (48%) | 47 (19–65) |
| VISION (Inpatient) | 526/1048 (50%) | 6058/10118 (60%) | 42 (34–49) |
| Influenza B | |||
| US Flu VE (Outpatient) | 1/1 (100%) | 300/439 (68%) | — |
| VISION (Outpatient) | 29/97 (30%) | 12162/19571 (62%) | 69 (51–80) |
| IVY (Inpatient) | 3/5 (60%) | 938/1945 (48%) | — |
| VISION (Inpatient) | 5/20 (25%) | 6058/10118 (60%) | — |
*VE was estimated using the test-negative design comparing vaccination odds among persons who tested positive for influenza to vaccination odds among persons who tested negative for any influenza and SARS-CoV-2. Calculated as (1 − adjusted OR) × 100%; ORs were estimated using logistic regression.
†Subtype was not available for VISION
¶All networks adjusted for geographic region, age, calendar time. IVY, US Flu VE, and VISION, adjusted for sex and race/ethnicity. US Flu VE also adjusted for time since illness onset and self-reported health status. VE estimates with fewer than 50 cases or from models that did not converge are not presented and are represented with a “—”
**Outpatient is defined as outpatient clinics, urgent care, and emergency departments for US Flu VE. Outpatient is defined as urgent care and emergency departments for VISION.
