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. 2019 Nov 13;69(11):1845-1853.
doi: 10.1093/cid/ciz075.

Effects of Influenza Vaccination in the United States During the 2017-2018 Influenza Season

Melissa A Rolfes  1 , Brendan Flannery  1 , Jessie R Chung  1 , Alissa O'Halloran  1 , Shikha Garg  1 , Edward A Belongia  2 , Manjusha Gaglani  3 , Richard K Zimmerman  4 , Michael L Jackson  5 , Arnold S Monto  6 , Nisha B Alden  7 , Evan Anderson  8 , Nancy M Bennett  9 , Laurie Billing  10 , Seth Eckel  11 , Pam Daily Kirley  12 , Ruth Lynfield  13 , Maya L Monroe  14 , Melanie Spencer  15 , Nancy Spina  16 , H Keipp Talbot  17 , Ann Thomas  18 , Salina M Torres  19 , Kimberly Yousey-Hindes  20 , James A Singleton  21 , Manish Patel  1 , Carrie Reed  1 , Alicia M Fry  1 ; US Influenza Vaccine Effectiveness (Flu VE) Network, the Influenza Hospitalization Surveillance Network, and the Assessment Branch, Immunization Services Division, Centers for Disease Control and Prevention
Collaborators, Affiliations

Effects of Influenza Vaccination in the United States During the 2017-2018 Influenza Season

Melissa A Rolfes et al. Clin Infect Dis. .

Abstract

Background: The severity of the 2017-2018 influenza season in the United States was high, with influenza A(H3N2) viruses predominating. Here, we report influenza vaccine effectiveness (VE) and estimate the number of vaccine-prevented influenza-associated illnesses, medical visits, hospitalizations, and deaths for the 2017-2018 influenza season.

Methods: We used national age-specific estimates of 2017-2018 influenza vaccine coverage and disease burden. We estimated VE against medically attended reverse-transcription polymerase chain reaction-confirmed influenza virus infection in the ambulatory setting using a test-negative design. We used a compartmental model to estimate numbers of influenza-associated outcomes prevented by vaccination.

Results: The VE against outpatient, medically attended, laboratory-confirmed influenza was 38% (95% confidence interval [CI], 31%-43%), including 22% (95% CI, 12%-31%) against influenza A(H3N2), 62% (95% CI, 50%-71%) against influenza A(H1N1)pdm09, and 50% (95% CI, 41%-57%) against influenza B. We estimated that influenza vaccination prevented 7.1 million (95% CrI, 5.4 million-9.3 million) illnesses, 3.7 million (95% CrI, 2.8 million-4.9 million) medical visits, 109 000 (95% CrI, 39 000-231 000) hospitalizations, and 8000 (95% credible interval [CrI], 1100-21 000) deaths. Vaccination prevented 10% of expected hospitalizations overall and 41% among young children (6 months-4 years).

Conclusions: Despite 38% VE, influenza vaccination reduced a substantial burden of influenza-associated illness, medical visits, hospitalizations, and deaths in the United States during the 2017-2018 season. Our results demonstrate the benefit of current influenza vaccination and the need for improved vaccines.

Keywords: burden; influenza; prevented illnesses; vaccination.

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Figures

Figure 1.
Figure 1.
Adjusted rates of influenza-associated (A) illnesses, (B) medical visits, (C) hospitalizations, and (D) deaths, by age group and influenza (sub)type—United States, 2017–2018 influenza season.
Figure 2.
Figure 2.
Adjusted vaccine effectiveness (VE) against outpatient, medically attended influenza-associated illness, US Flu VE Network—2017–2018 influenza season. The y-axis scale has been truncated for simplicity; however, for adults aged ≥65 years, the 95% confidence interval around the adjusted VE estimate against influenza A(H1N1)pdm09 extends beyond the lower limit of the y-axis (adjusted VE = 0.19, 95% confidence interval, –.91, .65).
Figure 3.
Figure 3.
Estimated percent of expected influenza-associated hospitalizations prevented by vaccination—United States, 2017–2018 influenza season.
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