Estimation of the Effectiveness of Quadrivalent Influenza Vaccines by Distinguishing Between Influenza A (H1N1) pdm09 and Influenza A (H3N2) Using Rapid Influenza Diagnostic Tests During the 2018-2019 Season.

Objective To estimate the effectiveness of quadrivalent influenza vaccines during the 2018-2019 season for influenza A (H1N1) pdm09 and A (H3N2) in all age groups. Methods A test-negative case-control study was performed. Patients A total of 1,331 participants were divided into 4 groups (younger children: ≤6 years, older children: 7-15 years, younger adults: 16-64 years, and older adults: ≥65 years). Results For all children, the adjusted vaccine effectiveness (VE) was significant against any influenza [41.3% (95% confidence interval (CI): 19.7-57.2%)], total A [A (H1N1) pdm09 and (H3N2); 38.3% (95% CI: 15.1-55.1%)], and A [H3N2; 39.8% (95% CI: 13.8-57.9%)]. In younger children, the adjusted VE against any influenza was 44.8% (95% CI: 14.1-64.5%) and against total A was 43.8% (95% CI: 12.5-63.9%). For all adults, the adjusted VE was significant against any influenza was 42.3% (95% CI: 17.9-59.5%); total A, 39.3% (95% CI: 13.5-57.4%); A (H1N1) pdm09, 56.7% (95% CI: 19.1-76.8%); and A (H3N2), 33.2% (95% CI: 1.5-54.6%). In younger adults, the adjusted VE against any influenza was 43.4% (95% CI: 17.3-61.2%), total A, 41.7% (95% CI: 14.4-60.3%); A (H1N1) pdm09, 56.2% (95% CI: 14.9-77.5%); and A (H3N2), 34.5% (95% CI: 0.3-56.9%). In both older children and older adults, no significant VE was observed. Conclusion This study is the first to report on the VE against all types of influenza in all age groups using a rapid influenza diagnostic test. The VE varied with both age and influenza subtype.