Estimated Influenza Illnesses, Medical Visits, Hospitalizations, and Deaths Prevented by Vaccination in the United States – 2022-2023 Influenza Season

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.

For more than a decade, CDC has used a model to estimate the numbers 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 States (1-6). The methods used to calculate the estimates of flu burden prevented by flu vaccination have been described previously (1,2,6). 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 6.0 million flu-related illnesses, 2.9 million medical visits, 65,000 hospitalizations, and 3,700 deaths (Table 1).

2022-23 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 children (7). The season had predominately influenza A virus circulation with subtype A(H3N2) viruses most commonly detected (8).

Preliminary estimates of the burden of disease during the 2022–2023 season was similar to some 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 (9).

CDC estimates that during the 2022-2023 season, 44% to 70% of people in the United States were vaccinated against flu (10). Flu vaccine effectiveness for the 2022-2023 season for all ages was 46%, but varied by age group and was highest for children 6 months to 4 years (54%) and lowest among adults 65 years and older (27%).  Based on the 2022-2023 flu disease burden estimates along with vaccine coverage and vaccine effectiveness data, CDC estimates that 6.0 million flu-related illnesses, 2.9 million flu-related health-care visits, 65,000 flu-related hospitalizations, and 3,700 flu-related deaths were prevented by flu vaccination. The number and proportion 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 (45%). 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 (27%).

Annual flu vaccination is the best way to protect against flu and associated complications. Several efforts are currently underway to understand and investigate factors that contribute to reduced or increased vaccine effectiveness and inform changes to vaccine composition, formulations, or production (11-13).

Improvements in vaccine coverage could also provide great public health benefit, producing even greater reductions in illnesses and lowering demands on the health system. During flu seasons, the health care system, including outpatient clinics, emergency departments, and hospitals, can experience high patient volumes. Any reduction in flu-related medical visits and hospitalizations can reduce demands on the health care systems and improve health care providers’ abilities to provide the best care. Strategies to improve flu vaccine coverage include: using patient reminder/recall systems aided by immunization information systems; expanding access to flu vaccination at pharmacies, workplaces, and schools; and organizing mobile and/or outdoor vaccination clinics.

Changes to data sources and methods to estimate prevented burden for the 2022-23 season

Vaccine effectiveness (VE) estimates for the 2022-23 flu season came from multiple studies. For children, VE estimates were derived from both inpatient and outpatient settings in the New Vaccine Surveillance Network (NVSN) and from the VISION Vaccine Effectiveness Network (14, 15). Adult VE data was derived from inpatient settings in the Investigating Respiratory Viruses in the Acutely Ill (IVY) Network (16, 17) and inpatient and outpatient settings in the VISION Vaccine Effectiveness Network (18). Because multiple estimates were available for the analytic age groups, the estimates were combined into an overall estimate of VE for each age group. To combine estimates, the available estimates were used to simulate normal distributions and the mean VE for each age group was used in the models of prevented burden.

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, influenza 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.

References

1. Kostova D, Reed C, Finelli L, Cheng PY, Gargiullo PM, Shay DK, et al. Influenza Illness and Hospitalizations Averted by Influenza Vaccination in the United States, 2005-2011. PLoS One. 2013;8(6):e66312.
2. Reed C, Chaves SS, Daily Kirley P, Emerson R, Aragon D, Hancock EB, et al. Estimating influenza disease burden from population-based surveillance data in the United States. PLoS One. 2015;10(3):e0118369.
3. Centers for Disease Control and Prevention. Estimated influenza illnesses and hospitalizations averted by influenza vaccination – United States, 2012-13 influenza season. MMWR Morb Mortal Wkly Rep. 2013 Dec 13;62(49):997-1000.
4. Reed C, Kim IK, Singleton JA, Chaves SS, Flannery B, Finelli L, et al. Estimated influenza illnesses and hospitalizations averted by vaccination–United States, 2013-14 influenza season. MMWR Morb Mortal Wkly Rep. 2014 Dec 12;63(49):1151-4.
5. Centers for Disease Control and Prevention. Estimated Influenza Illnesses and Hospitalizations Averted by Vaccination — United States, 2014–15 Influenza Season. 2015 December 10, 2015 [cited 2016 October 27]; Available from: http://www.cdc.gov/flu/about/disease/2014-15.htm
6. Tokars JI, Rolfes MA, Foppa IM, Reed C. An evaluation and update of methods for estimating the number of influenza cases averted by vaccination in the United States. Vaccine. 2018 Nov 19;36(48):7331-7.
7. How CDC Classifies Flu Severity. https://www.cdc.gov/flu/about/classifies-flu-severity.htm
8. Influenza Activity in the United States during the 2022–23 Season and Composition of the 2023–24 Influenza Vaccine https://www.cdc.gov/flu/spotlights/2023-2024/22-23-summary-technical-report.htm
9. Preliminary Estimated Influenza Illnesses, Medical Visits, Hospitalizations, and Deaths in the United States — 2022–2023 Influenza Season. https://www.cdc.gov/flu/about/burden/2022-2023.htm
10. Centers for Disease Control and Prevention. Influenza Vaccination Coverage; Available from: https://www.cdc.gov/flu/fluvaxview/
11. Hwang HS, Chang M, Kim YA. Influenza-Host Interplay and Strategies for Universal Vaccine Development. Vaccines. 2020 Sep 20;8(3).
12. Viboud C, Gostic K, Nelson MI, Price GE, Perofsky A, Sun K, et al. Beyond clinical trials: Evolutionary and epidemiological considerations for development of a universal influenza vaccine. PLoS Pathog. 2020 Sep;16(9):e1008583.
13. Centers for Disease Control and Prevention. CDC Seasonal Flu Vaccine Effectiveness Studies. 2022 October 22, 2022 [cited 2022 November 30]; Available from: https://www.cdc.gov/flu/vaccines-work/effectiveness-studies.htm
14. New Vaccine Surveillance Network (NVSN). https://www.cdc.gov/flu/vaccines-work/2022-2023.html
15. Adams K, Weber ZA, Yang DH, Klein NP, DeSilva MB, Dascomb K, Irving SA, Naleway AL, Rao S, Gaglani M, Flannery B. Vaccine Effectiveness Against Pediatric Influenza-A-Associated Urgent Care, Emergency Department, and Hospital Encounters During the 2022–2023 Season, VISION Network. Clinical Infectious Diseases. 2023 Nov 16:ciad704.Investigating
16. Respiratory Viruses in the Acutely Ill (IVY) Network. https://www.cdc.gov/flu/vaccines-work/ivy.htm
17. The Influenza and Other Viruses in the Acutely Ill (IVY) Network. https://www.ivy-network.org/
18. Tenforde MW, Weber ZA, Yang D-H, DeSilva MB, Dascomb K, Irving SA, Naleway AL, Gaglani M, Fireman B, Lewis N, Zerbo O, Goddard K, Timbol J, Hansen JR, Grisel N, Arndorfer J, McEvoy CE, Essien IJ, Rao S, Grannis SJ, Kharbanda AB, Natarajan K, Ong TC, Embi PJ, Ball SW, Dunne MM, Kirshner L, Wiegand RE, Dickerson M, Patel P, Ray C, Flannery B, Garg S, Adams K, Klein NP, Influenza vaccine effectiveness against influenza-A-associated emergency department, urgent care, and hospitalization encounters among U.S. adults, 2022-2023, The Journal of Infectious Diseases, 2023;, jiad542, https://doi.org/10.1093/infdis/jiad542