Spread of antigenically drifted influenza A (H3N2) viruses and vaccine effectiveness in the United States during the 2018–2019 season
B Flannery, RJG Kondor, JR Chung… - The Journal of …, 2020 - academic.oup.com
B Flannery, RJG Kondor, JR Chung, M Gaglani, M Reis, RK Zimmerman, MP Nowalk…
The Journal of infectious diseases, 2020•academic.oup.comBackground Increased illness due to antigenically drifted A (H3N2) clade 3C. 3a influenza
viruses prompted concerns about vaccine effectiveness (VE) and vaccine strain selection.
We used US virologic surveillance and US Influenza Vaccine Effectiveness (Flu VE) Network
data to evaluate consequences of this clade. Methods Distribution of influenza viruses was
described using virologic surveillance data. The Flu VE Network enrolled ambulatory care
patients aged≥ 6 months with acute respiratory illness at 5 sites. Respiratory specimens …
viruses prompted concerns about vaccine effectiveness (VE) and vaccine strain selection.
We used US virologic surveillance and US Influenza Vaccine Effectiveness (Flu VE) Network
data to evaluate consequences of this clade. Methods Distribution of influenza viruses was
described using virologic surveillance data. The Flu VE Network enrolled ambulatory care
patients aged≥ 6 months with acute respiratory illness at 5 sites. Respiratory specimens …
Background
Increased illness due to antigenically drifted A(H3N2) clade 3C.3a influenza viruses prompted concerns about vaccine effectiveness (VE) and vaccine strain selection. We used US virologic surveillance and US Influenza Vaccine Effectiveness (Flu VE) Network data to evaluate consequences of this clade.
Methods
Distribution of influenza viruses was described using virologic surveillance data. The Flu VE Network enrolled ambulatory care patients aged ≥6 months with acute respiratory illness at 5 sites. Respiratory specimens were tested for influenza by means of reverse-transcriptase polymerase chain reaction and were sequenced. Using a test-negative design, we estimated VE, comparing the 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 2763 Flu VE Network case patients, 1325 (48%) were infected with A(H1N1)pdm09 and 1350 (49%) with A(H3N2); clade 3C.3a accounted for 977 (93%) of 1054 sequenced A(H3N2) viruses. VE was 44% (95% confidence interval, 37%–51%) against A(H1N1)pdm09 and 9% (−4% to 20%) against A(H3N2); VE was 5% (−10% to 19%) against A(H3N2) clade 3C.3a viruses.
Conclusions
The predominance of A(H3N2) clade 3C.3a viruses during the latter part of the 2018–2019 season was associated with decreased VE, supporting the A(H3N2) vaccine component update for 2019–2020 northern hemisphere influenza vaccines.
Oxford University Press