Flu Burden Prevented from Vaccination 2022-2023 Flu Season

What to know

This web page provides estimates on the burden of influenza (flu) and the effects of annual flu vaccination in the United States for the 2022–2023 season.

Background

For more than a decade, CDC has used a model to estimate the annual number of flu illnesses, medical visits, hospitalizations, and deaths during the flu season, and to estimate the impact that flu vaccination had on illness outcomes in the United States123456. The methods used to calculate the estimates of flu burden prevented by flu vaccination have been described previously16. CDC uses the estimates of the impact of flu vaccination to inform policy and communications promoting vaccination as the best way to prevent flu.

CDC estimates that during the 2022-2023 season, flu vaccination prevented 5.5 million flu-related illnesses, 2.7 million medical visits, 71,000 hospitalizations, and 4,300 deaths.

Changes to data sources and methods to estimate prevented burden for the 2022-2023 season

Vaccine effectiveness (VE) estimates for the 2022-23 flu season came from multiple studies. For children, VE estimates were derived for both inpatient and outpatient settings using data from the New Vaccine Surveillance Network (NVSN) and from the VISION Vaccine Effectiveness Network 78. The US Flu Vaccine Effectiveness (VE) Network15 also provided VE estimates for outpatient settings for both children and adults. The Investigating Respiratory Viruses in the Acutely Ill (IVY) Network 910provided adult VE estimates for inpatient settings and the VISION Vaccine Effectiveness Network 11provided both adult VE estimates for both inpatient and outpatient settings. Because multiple estimates were available for the analytic age groups, the estimates were combined into an overall estimate of VE for each age group and setting (i.e., inpatient and outpatient). To combine estimates, the available estimates were used to simulate normal distributions and the mean VE for each age group and setting was used in the models of prevented burden.

2022-2023 Flu Burden Prevented by Vaccination

Compared with past flu seasons, the 2022–2023 season was considered a moderate severity season with high severity observed among children12. The season had predominately influenza A virus circulation with subtype A(H3N2) viruses most commonly detected 13.

Preliminary estimates of the burden of disease during the 2022–2023 season were similar to seasons before the pandemic, with 31 million people developing flu illness, 14 million visiting a health care provider for flu, 360,000 hospitalizations for flu, and 21,000 flu deaths 13.

CDC estimates that during the 2022-2023 season, 44% to 70% of people depending upon the age group in the United States were vaccinated against flu 14. Flu vaccine effectiveness for the 2022-2023 season in outpatient settings ranged from 40% to 52%, with the highest VE among children and the lowest among older adults 147815910. VE in inpatient settings ranged from 31-57% and was highest among children 5-17 years of age and lowest among adults ages 18-49 years 781591011. Based on the 2022-2023 flu disease burden estimates along with vaccine coverage and vaccine effectiveness data, CDC estimates that 5.5 million flu-related illnesses, 2.7 million flu-related health-care visits, 71,000 flu-related hospitalizations, and 4,300 flu-related deaths were prevented by flu vaccination. The number of flu-related illnesses, medically attended illnesses, hospitalizations, and deaths prevented by vaccination during 2022–2023 varied by age group, due to age-specific differences in flu burden, vaccine coverage, and vaccine effectiveness. Flu vaccination prevented the highest number of community illnesses and medically attended illnesses among children aged 5-17 years, an age group in which vaccine uptake (55%) and vaccine effectiveness was moderate ranging from 45% in outpatient settings to 55% in inpatient settings. Conversely, flu vaccination prevented the highest number of hospitalizations and deaths among adults aged 65 years and older, an age group with approximately 70% vaccine coverage and for whom flu vaccine effectiveness was lowest in inpatient settings (37%) and highest in outpatient settings (40%).

Estimated Number of Flu-Related Illnesses, Medical Visits, Hospitalizations, and Deaths Prevented by Vaccination, by Age Group—United States, 2022-2023 Flu Season

Table 1: Estimated Number of Flu-Related Illnesses, Medical Visits, Hospitalizations, and Deaths Prevented by Vaccination, by Age Group—United States, 2022-2023 Flu Season
Symptomatic Illnesses Medical Visits Hospitalizations Deaths
Age group Vaccine Coverage (%) Outpatient Adjusted VE (95% CI) Inpatient Adjusted VE (95% CI) Estimate 95% UI Estimate 95% UI Estimate 95% UI Estimate 95% UI
Influenza, all flu
6 months-4 years 65.1% 51.9% (51.6, 52.3) 54.8% (54.3, 55.3) 798,981 (662,511, 1,315,935) 535,317 (415,063, 883,391) 5,996 (4,668, 9,901) 57 (9, 125)
5-17 years 54.7% 45.2% (44.4, 46) 56.5% (55.8, 57.1) 1,764,684 (1,323,206, 3,880,721) 917,635 (679,786, 2,029,713) 6,433 (4,817, 14,249) 65 (17, 232)
18-49 years 34.8% 44.3% (43.6, 45.1 31.1% (30.7, 31.6) 1,246,783 (907,676, 2,145,405) 416,310 (332,035, 800,766) 4,741 (3,459, 8,155) 83 (32, 173)
50-64 years 49.5% 42.2% (41.2, 43.2) 32.1% (31.7, 32.5) 1,114,968 (793,736, 2,432,833) 479,436 (337,272, 1,040,437) 8,599 (6,135, 19,708) 615 (187, 1,312)
65+ years 69.0% 39.8% (38.1, 41.4) 36.6% (36.4, 36.8) 549,487 (373,007, 1,257,887) 307,713 (208,040, 709,373) 44,983 (30,633, 102,959) 3,503 (1,587, 12,087)
All ages 45.2% (44.9, 45.5) 39.9% (39.2, 40.5) 5,474,903 (4,647,447, 8,371,773) 2,701,412 (2,297,385, 4,164,986) 70,753 (55,813, 130,930) 4,322 (2,250, 12,947)

Conclusion

CDC estimates that during the 2022-2023 season flu vaccination contributed to meaningful reductions in the impact of flu. This report underscores the benefits of the current flu vaccination program but highlights areas where improvements in flu vaccine uptake and vaccine effectiveness could deliver even greater benefits to the public’s health.

Limitations

These estimates are subject to several limitations. First, flu vaccination coverage estimates were derived from reports by survey respondents, not vaccination records, and are subject to recall bias. These coverage estimates are based on telephone surveys with relatively low response rates; non-response bias may remain after weighting for the survey design. Estimates of the number of people vaccinated based on these survey data have often exceeded the actual number of flu vaccine doses distributed, indicating that coverage estimates used in this report may overestimate the numbers of flu illnesses and hospitalizations prevented by flu vaccination. The model of prevented flu illnesses calculates outcomes directly prevented among people who were vaccinated. If indirect protection from decreased exposure to infectious people in a partially flu-vaccinated population (i.e., herd immunity) also occurred, the model would underestimate the number of flu illnesses and hospitalizations prevented by flu vaccination. Finally, because the data and methods used to make these calculations are continually updated, current estimates are preliminary and will be updated when final data are available.

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National Center for Immunization and Respiratory Diseases (NCIRD)
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