Influenza vaccine effectiveness against influenza A in children based on the results of various rapid influenza tests in the 2018/19 season.

During influenza epidemics, Japanese clinicians routinely conduct rapid influenza diagnostic tests (RIDTs) in patients with influenza-like illness, and patients with positive test results are treated with anti-influenza drugs within 48 h after the onset of illness. We assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children (6 months-15 years old, N = 4243), using a test-negative case-control design based on the results of RIDTs in the 2018/19 season. The VE against influenza A(H1N1)pdm and A(H3N2) was analyzed separately using an RIDT kit specifically for detecting A(H1N1)pdm09. The adjusted VE against combined influenza A (H1N1pdm and H3N2) and against A(H1N1)pdm09 was 39% (95% confidence interval [CI], 30%-46%) and 74% (95% CI, 39%-89%), respectively. By contrast, the VE against non-A(H1N1)pdm09 influenza A (presumed to be H3N2) was very low at 7%. The adjusted VE for preventing hospitalization was 56% (95% CI, 16%-77%) against influenza A. The VE against A(H1N1)pdm09 was consistently high in our studies. By contrast, the VE against A(H3N2) was low not only in adults but also in children in the 2018/19 season.
Competing Interests: We have read the journal’s policy and the authors of this manuscript have the following competing interests: within 36 months, Dr. Norio Sugaya has received speakers’ honoraria from Chugai, Shionogi, Daiichi Sankyo, Astellas, Merck, and Denka Seiken. Dr. Masayoshi Shinjoh has received speakers’ honoraria from Shionogi, Meiji Seika, Merck, Sumitomo Dainippon, Japan Vaccine, Maruho, Astellas, Daiichi Sankyo, and grant support from Janssen. Dr. Keiko Mitamura has received speakers’ honoraria from Shionogi, Meiji Seika, and manuscript fee from Astellas. Dr. Takao Takahashi has received speakers’ honoraria from Daiichi Sankyo, GlaxoSmithKline, Japan Vaccine, Pfizer, Merck, and grant support from Daiichi Sankyo, Japan Vaccine, Pfizer, Merck, Takeda, and Astellas. Other authors have no competing interests regarding this study. This does not alter our adherence to PLOS ONE policies on sharing data and materials.