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

Abstract

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.

Trends in effectiveness of inactivated influenza vaccine in children by age groups in seven seasons immediately before the COVID-19 era

“…Although children aged 6-11 months are included in the recommended group, the vaccine effectiveness (VE) for this specific age group has not been proved recently. Our series of VE studies since the 2013/14 season [7] , [9] , [10] , [11] , [12] , [13] demonstrated that vaccines in younger (6–11 months) and older (6–15 years old) children tended to be less effective. We showed significant VE against influenza A in the 2018/19 season for children aged 6–11 months (63% [95% confidence interval (CI), 15–84]) [7] , but the VE for this age was not statistically significant against either influenza A and B in other seasons (95%CI of the odds ratio included 1.0).…”

“…Our series of VE studies since the 2013/14 season [7] , [9] , [10] , [11] , [12] , [13] demonstrated that vaccines in younger (6–11 months) and older (6–15 years old) children tended to be less effective. We showed significant VE against influenza A in the 2018/19 season for children aged 6–11 months (63% [95% confidence interval (CI), 15–84]) [7] , but the VE for this age was not statistically significant against either influenza A and B in other seasons (95%CI of the odds ratio included 1.0). In one of our studies in the five-season analysis (2013/14–2017/18) [13] , all age groups (1–2, 3–5, 6–12 years old) except 6-11 months showed significant VE for both influenza A and B.…”

“…We enrolled children who were 6 months to 15 years old with a fever of ≥38°C who were suspected of having influenza and had received an RIDT at one of our outpatient clinics at 20 hospitals in the north (Gunma, Tochigi), middle (Saitama, Tokyo, Chiba), and south (Kanagawa, and Shizuoka) Kanto region in Japan between the 2013/14 and 2020/21 seasons (November 1–March 31). The data were obtained from the database that we used in our recent VE studies, including the risk analysis study [7] , [9] , [10] , [11] , [12] , [13] , [14] .…”

“…The overall vaccine coverage rate in Japan remained low at approximately 30%, 60%, and 40% for children aged 1, 2-12, and 13-15 years, respectively [6] . A two-dose regimen is recommended for all children aged 6 months to 12 years old regardless of recent immunization histories, and a single dose is recommended only for children 13 years and older in Japan [7] . In the United States, children who previously received ≥2 total doses of influenza vaccine ≥4 weeks apart before July 1 of the season require only one dose for the season, and others require two [8] .…”

Relationship Between Medical Questionnaire and Influenza Rapid Test Positivity: Subjective Pretest Probability, “I Think I Have Influenza,” Contributes to the Positivity Rate

“…Also, in Japan, patients need the certification of the RIDT results, regardless that they are positive or negative, to go to work or be on sick leave when they have colds during the influenza pandemic season. Therefore, Japanese clinicians routinely use RIDTs as a complementary exam with influenza-like illnesses, and most positive patients are treated with anti-influenza drugs [ 2 ]. Doctors also tend to depend on RIDTs because there are few specific physical findings to influenza [ 3 ].…”