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J Infect Dis. 2019 Oct 30. pii: jiz543. doi: 10.1093/infdis/jiz543. [Epub ahead of print]

Spread of antigenically drifted influenza A(H3N2) viruses and vaccine effectiveness in the United States during the 2018-2019 season.

Author information

1
Influenza Division, Centers for Disease Control and Prevention, Atlanta GA.
2
Baylor Scott & White Health, Texas A&M University Health Science Center College of Medicine, Temple TX.
3
University of Pittsburgh Schools of Health Sciences and UPMC, Pittsburgh PA.
4
Kaiser Permanente Washington Health Research Institute, Seattle WA.
5
University of Michigan School of Public Health, Department of Epidemiology, Ann Arbor MI.
6
Marshfield Clinic Research Institute, Marshfield WI.
7
Oak Ridge Institute for Science and Education Fellowship Program, Oak Ridge TN.

Abstract

BACKGROUND:

Increased illness due to antigenically drifted A(H3N2) clade 3C.3a influenza viruses prompted concerns about vaccine effectiveness and vaccine strain selection. We used U.S. virologic surveillance and Influenza Vaccine Effectiveness (VE) Network data to evaluate consequences of this clade.

METHODS:

Distribution of influenza viruses was described using virologic surveillance data. The VE Network enrolled ambulatory patients aged ≥6 months with acute respiratory illness at five sites. Respiratory specimens were tested by RT-PCR for influenza and sequenced. Using a test-negative design, we estimated VE comparing odds of influenza among vaccinated versus unvaccinated participants.

RESULTS:

During the 2018-2019 influenza season, A(H3N2) clade 3C.3a viruses caused an increasing proportion of influenza cases. Among 2,763 VE Network case patients, 1,325 (48%) were infected with A(H1N1)pdm09 and 1,350 (49%) with A(H3N2); clade 3C.3a accounted for 977 (93%) of 1,054 sequenced A(H3N2) viruses. VE was 44% (95% confidence interval [CI], 37 to 51%) against A(H1N1)pdm09 and 9% (95% CI, -4 to 20%) against A(H3N2); effectiveness was 5% (95% CI, -10 to 19%) against A(H3N2) clade 3C.3a viruses.

CONCLUSIONS:

Predominance of A(H3N2) clade 3C.3a viruses during the latter part of the 2018-2019 season was associated with decreased vaccine effectiveness, supporting the A(H3N2) vaccine component update for 2019-2020 northern hemisphere influenza vaccines.

PMID:
31665373
DOI:
10.1093/infdis/jiz543

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