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Master of Public Health

Influenza Vaccine Effectiveness Against Influenza A(H3N2)-Related Illness in the United States During the 2021-2022 Influenza Season

AUTHORS

Price AM , Flannery B , Talbot HK , Grijalva CG , Wernli KJ , Phillips CH , Monto AS , Martin ET , Belongia EA , McLean HQ , Gaglani M , Mutnal M , Geffel KM , Nowalk MP , Tartof SY , Florea A , McLean C , Kim SS , Patel MM , Chung JR , . Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2022 12 12; ().

ABSTRACT

BACKGROUND: In the United States, influenza activity during the 2021-2022 season was modest and sufficient enough to estimate influenza vaccine effectiveness for the first time since the beginning of the COVID-19 pandemic. We estimated influenza vaccine effectiveness against lab-confirmed outpatient acute illness caused by predominant A(H3N2) viruses.

METHODS: Between October 2021 and April 2022, research staff across 7 sites enrolled patients aged ≥6 months seeking outpatient care for acute respiratory illness with cough. Using a test-negative design, we assessed VE against influenza A(H3N2). Due to strong correlation between influenza and SARS-CoV-2 vaccination, participants who tested positive for SARS-CoV-2 were excluded from vaccine effectiveness estimations. Estimates were adjusted for site, age, month of illness, race/ethnicity and general health status.

RESULTS: Among 6,260 participants, 468 (7%) tested positive for influenza only, including 440 (94%) for A(H3N2). All 206 sequenced A(H3N2) viruses were characterized as belonging to genetic group 3C.2a1b subclade 2a.2, which has antigenic differences from the 2021-2022 season A(H3N2) vaccine component that belongs to clade 3C.2a1b subclade 2a.1. After excluding 1,948 SARS-CoV-2 positive patients, 4,312 patients were included in analyses of influenza VE; 2,463 (57%) were vaccinated against influenza. Effectiveness against A(H3N2) for all ages was 36% (95%CI, 20-49%) overall.

CONCLUSION: Influenza vaccination in 2021-2022 provided protection against influenza A(H3N2)-related outpatient visits among young persons.

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