Vaccine effectiveness against influenza A(H3N2)-associated hospitalized illness, United States, 2022.
Clin Infect Dis
; 2022 Nov 03.
Article
in English
| MEDLINE | ID: covidwho-2283784
ABSTRACT
BACKGROUND:
The COVID-19 pandemic was associated with historically low influenza circulation during the 2020-2021 season, followed by increase in influenza circulation during the 2021-2022 US season. The 2a.2 subgroup of the influenza A(H3N2) 3C.2a1b subclade that predominated was antigenically different from the vaccine strain.METHODS:
To understand the effectiveness of the 2021-2022 vaccine against hospitalized influenza illness, a multi-state sentinel surveillance network enrolled adults aged ≥18 years hospitalized with acute respiratory illness (ARI) and tested for influenza by a molecular assay. Using the test-negative design, vaccine effectiveness (VE) was measured by comparing the odds of current season influenza vaccination in influenza-positive case-patients and influenza-negative, SARS-CoV-2-negative controls, adjusting for confounders. A separate analysis was performed to illustrate bias introduced by including SARS-CoV-2 positive controls.RESULTS:
A total of 2334 patients, including 295 influenza cases (47% vaccinated), 1175 influenza- and SARS-CoV-2 negative controls (53% vaccinated), and 864 influenza-negative and SARS-CoV-2 positive controls (49% vaccinated), were analyzed. Influenza VE was 26% (95%CI -14 to 52%) among adults aged 18-64 years, -3% (95%CI -54 to 31%) among adults aged ≥65 years, and 50% (95%CI 15 to 71%) among adults 18-64 years without immunocompromising conditions. Estimated VE decreased with inclusion of SARS-CoV-2-positive controls.CONCLUSIONS:
During a season where influenza A(H3N2) was antigenically different from the vaccine virus, vaccination was associated with a reduced risk of influenza hospitalization in younger immunocompetent adults. However, vaccination did not provide protection in adults ≥65 years of age. Improvements in vaccines, antivirals, and prevention strategies are warranted.
Full text:
Available
Collection:
International databases
Database:
MEDLINE
Type of study:
Experimental Studies
/
Observational study
/
Prognostic study
Topics:
Vaccines
Language:
English
Journal subject:
Communicable Diseases
Year:
2022
Document Type:
Article
Affiliation country:
Cid
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