Effectiveness of current and repeated vaccination with quadrivalent influenza vaccine during the 2017/18 season in Japan

Abstract

The effectiveness of repeated vaccination of the quadrivalent influenza vaccine is currently unknown. This study aims to estimate current and repeated vaccination effectiveness (VE) of the quadrivalent influenza vaccine. A test-negative casecontrol study was performed during the 2017–2018 season. The participants were Japanese children divided into four groups (6–11 months and ages 1–5, 6–12, and 13–15 years). Current VE: Overall, the adjusted VE was significant for influenza B (36.4; 95% confidence interval [CI]: 9.8–55.2); the adjusted VE was significant for any influenza (A+B; 47.3%; 95% CI: 12.2–68.3) and influenza B (56.2%; 95% CI: 17.9–76.6) only in the 1–5 year age group. In other groups, VE was not observed. Vaccine doses: Two vaccine doses significantly decreased the incidence of any influenza and influenza B compared to no vaccination or only one dose in only the 1–5 year old group. Repeated VE: The adjusted VE was significant for any influenza (72.6%; 95% CI: 27.1–89.7) and influenza B (69.7%; 95% CI: 4.5–90.4) in only the 1–5-year age group without vaccination in the previous season. It was also significant for influenza B (68.6%; 95% CI: 1.3–90.0) in the 6–12-year age group with two vaccination doses in the previous season. In other groups, repeated VE was not observed for any influenza types. The reason for that repeated VE may depend on age, repeated vaccination with two doses may be valuable in the 6–12 year age group, although current VE was not observed.