No association between inactivated influenza vaccination and influenza viral load at diagnosis among young Japanese children: An observational study of the 2013/2014 through 2017/2018 influenza seasons.

BACKGROUND: The association between inactivated influenza vaccination and viral load in young children remains unclear. METHODS: During the 2013/2014 to 2017/2018 influenza seasons in Japan, children under 6 years of age with pre-defined influenza-like illness and influenza-positive status by real-time RT-PCR were recruited at pediatric clinics for this observational study. Influenza viral load was measured for the most predominant subtype/lineage in each season. Using median dichotomized viral load as an outcome, a multilevel logistic regression model was applied to estimate the multivariable adjusted odds ratio (MOR) and 95% confidence interval (CI) for higher viral load. RESULTS: A total of 1,185 influenza-positive children were analyzed. The median log10 viral load copy number (copies per milliliter) was 5.5 (interquartile range, 4.6 to 6.1) and did not differ by vaccination status: 5.5 for unvaccinated, 5.7 for one dose, and 5.5 for two doses (p = 0.67). The MOR of vaccinated (one or two doses) versus unvaccinated children was 1.19 (95% CI: 0.86-1.64). Other factors showing significant associations with higher viral load were positive results for A(H1N1)pdm09 and A(H3N2) in comparison with B/Yamagata. The respective MORs were 3.25 (95% CI: 2.28-4.64) and 1.81 (95% CI: 1.32-2.49). Significantly elevated MORs against higher viral load were also observed for higher body temperature at influenza diagnosis and shorter duration from fever onset to specimen collection. CONCLUSION: No association was observed between inactivated-influenza vaccination and viral load at influenza-positive diagnosis. Influenza subtype/lineage, body temperature, and time elapsed since fever onset were significantly associated with viral load.

Influence of Prior Influenza Vaccination on Current Influenza Vaccine Effectiveness in Children Aged 1 to 5 Years.

BACKGROUND: Although annual influenza vaccination is an important strategy used to prevent influenza-related morbidity and mortality, some studies have reported the negative influence of prior vaccination on vaccine effectiveness (VE) for current seasons. Currently, the influence of prior vaccination is not conclusive, especially in children. METHODS: We evaluated the association between current-season VE and prior season vaccination using a test-negative design in children aged 1-5 years presenting at nine outpatient clinics in Japan during the 2016/17 and 2017/18 influenza seasons. Children with influenza-like illness were enrolled prospectively and tested for influenza using real-time RT-PCR. Their recent vaccination history was categorized into six groups according to current vaccination doses (0/1/2) and prior vaccination status (unvaccinated = 0 doses/vaccinated = 1 dose or 2 doses): (1) 0 doses in the current season and unvaccinated in prior seasons (reference group); (2) 0 doses in the current season and vaccinated in a prior season; (3) 1 dose in the current season and unvaccinated in a prior season; (4) 1 dose in the current season and vaccinated in a prior season; (5) 2 doses in the current season and unvaccinated in a prior season, and (6) 2 doses in the current season and vaccinated in a prior season. RESULTS: A total of 799 cases and 1196 controls were analyzed. The median age of the subjects was 3 years, and the proportion of males was 54%. Overall, the vaccination rates (any vaccination in the current season) in the cases and controls were 36% and 53%, respectively. The VEs of the groups were: (2) 29% (95% confidence interval: -25% to 59%); (3) 53% (6% to 76%); (4) 70% (45% to 83%); (5) 56% (32% to 72%), and (6) 61% (42% to 73%). The one- and two-dose VEs of the current season were significant regardless of prior vaccination status. The results did not differ when stratified by influenza subtype/lineage. CONCLUSION: Prior vaccination did not attenuate the current-season VE in children aged 1 to 5 years, supporting the annual vaccination strategy.

[Evaluation of a new immunochromatographic kit for enhanced detection of influenza B virus].

We have evaluated a new immunochromatographic kit, "KBM LineCheck Flu AB", which had been developed for enhanced detection of influenza B viruses. Five strains of influenza A and B viruses were tested for reactivity and detection limits of the kit. Compared with the detection limits of commercially available kit of QuickNavi-Flu, "KBM LineCheck Flu AB" showed a nearly equal reactivity to influenza A viruses, but quadruple reactivity to 2 influenza B viruses. Also, "KBM LineCheck Flu AB" exhibited high specificity when tested in 130 influenza-negative culture specimens derived from 24 adult volunteers. Furthermore, "KBM LineCheck Flu AB" was clinically evaluated by using 866 specimens, including 190 nasal swabs, 201 nasal aspirations, 262 self-blown nasal discharges, and 213 pharyngeal swabs. Compared with the results of QuickNavi-Flu for influenza A, the test efficiency for the nasal swabs, the nasal aspirations, self-blown nasal discharges, and pharyngeal swabs were calculated to be 95.8%, 92.0%, 95.0%, and 94.8%, respectively. Whereas, as to influenza B, the test efficiency for the nasal swabs, the nasal aspirations, self-blown nasal discharges, and pharyngeal swabs was calculated to be 96.3%, 98.5%, 96.2%, and 93.4%, respectively. Similarly, compared with the results of influenza A viral culture, the test efficiency for the nasal swabs, the nasal aspirations, self-blown nasal discharges, and pharyngeal swabs was calculated to be 95.3%, 91.0%, 93.9%, and 92.5%, respectively. Regarding influenza B culture, the test efficiency for the nasal swabs, the nasal aspirations, self-blown nasal discharges, and pharyngeal swabs were calculated to be 95.8%, 97.5%, 95.1%, 91.5%, respectively. Overall, we concluded that the "KBM LineCheck Flu AB" is useful and suitable for diagnosis of influenza A and especially influenza B.