Prior vaccinations improve immunogenicity of inactivated influenza vaccine in young children aged 6 months to 3 years: A cohort study.

In young children, infrequent antigen exposure, which is partly characterized by fewer vaccinations, may be a factor impairing the immunogenicity of inactivated influenza vaccine.We assessed the effects of prior vaccinations on age-specific immune responses in Japanese children aged 6 months to 3 years, using data from a cohort study with 266 children who had received 2 doses (0.25 mL/dose for < 3 years old, 0.5 mL/dose for 3 years old) in the 2006/2007 season. Serological measures, primarily seroprotection rates, between previously vaccinated and vaccine-naïve children were compared within 1-year age strata. The seroprotection rate was defined in 2 ways as the proportion of subjects who achieved an antibody titer of 1:40 or 1:160. Multivariate logistic regression was also performed to estimate the independent effect of prior vaccination on seroprotection rate.After the first dose, seroprotection rates with the threshold of 1:40 in vaccine-naïve 1-year-olds remained low (28% for AH1, 26% for AH3, 2% for B), similar to those of 0-year-olds. In contrast, seroprotection rates in previously vaccinated 1-year-olds (77% for AH1, 86% for AH3, 18% for B) were significantly higher than those in vaccine-naïve 1-year-olds. These seroprotection rates for AH1 and AH3 were comparable with those in previously vaccinated 2- and 3-year-olds. Although seroprotection rates for B remained low in every age stratum even after the second dose, seroprotection rate in previously vaccinated 1-year-olds (50%) was similar to that in 3-year-olds. After adjustment for age, baseline antibody titer and experience of acute febrile respiratory illness in the preceding season, odds ratios showed a significant independent positive effect of prior vaccination on seroprotection rate for every strain. After the seroprotection threshold was changed from 1:40 to 1:160, the results of the effects of prior vaccinations on immunogenicity were similar or became more evident, which demonstrate the robustness of our findings.Our study found that prior vaccinations improved poor immunogenicity among young children, especially in 1-year-olds.

Pharmacokinetics of the antiepileptic drug levetiracetam in healthy Japanese and Caucasian volunteers following intravenous administration.

The intravenous (iv) formulation of levetiracetam has been available in clinical practice worldwide for several years, but not in Japan. Two open-label studies were conducted: Study A evaluated the bioequivalence of iv and oral tablet formulations in healthy Japanese volunteers; and Study B subsequently compared the pharmacokinetics of iv levetiracetam in healthy Japanese and Caucasian volunteers. Study A had a randomised, two-way crossover design; a single 1,500 mg levetiracetam dose was administered as a 15-min iv infusion and as 3 × 500 mg oral tablets to Japanese volunteers. In Study B, 1,500 mg levetiracetam was administered as single and repeated 15-min iv infusions to Japanese and Caucasian volunteers. Overall, 26/27 volunteers completed Study A and 32/32 (16 Japanese; 16 Caucasian) completed Study B. In Study A, the point estimate and 90 % confidence interval (CI) for the geometric least squares mean (LSM) ratio (iv vs oral) were fully included within the acceptance range for bioequivalence (0.85-1.25) for the area under plasma concentration-time curve from 0 to last quantifiable observation (AUClast 0.97 [0.95, 0.99]), but not for the maximum plasma concentration (C max 1.64 [1.47, 1.83]). In Study B, after a single iv infusion, the point estimates (90 % CI) for the geometric LSM ratio (Japanese vs Caucasian) for body weight-normalised C max and AUClast were 1.21 (1.07, 1.36) and 0.97 (0.90, 1.04), respectively. Corresponding values after repeated iv infusions were C max,ss 1.01 (0.91, 1.12) and AUCτ,ss 0.89 (0.83, 0.96). Levetiracetam was well tolerated in both studies. Study A did not demonstrate the bioequivalence of single doses of levetiracetam 1,500 mg administered as an iv infusion and as oral tablets in healthy Japanese adults. Study B, however, showed that pharmacokinetic profiles were generally similar between Japanese and Caucasian adults after single and repeated iv infusions of levetiracetam 1,500 mg.

Immunogenicity of the trivalent inactivated influenza vaccine in young children less than 4 years of age, with a focus on age and baseline antibodies.

In this study, we assessed the effects of the prevaccination titer and age on the immunogenicity of a low dose of influenza vaccine in children less than 4 years of age. A total of 259 children received two vaccine doses (0.1 ml for 0-year-olds and 0.2 ml for children 1 year of age or older) 4 weeks apart during the 2005/2006 season. The hemagglutination inhibition antibody titers were measured before vaccination and 4 weeks after the first and second doses. The geometric mean titer, mean fold rise, seroresponse proportion (≥4-fold rise in titer), and seroprotection proportion (titer ≥1:40) were calculated for the prevaccination titer and age categories. A multivariate logistic regression analysis was performed using the seroresponse and seroprotection proportions as dependent variables and the prevaccination titer and age as explanatory variables. As for the seroresponse against the H1 antigen after the first dose, the adjusted odds ratios of the prevaccination titers (versus <1:10) were 2.2 (95% confidence interval, 0.8 to 5.8) at 1:10 to 1:20 and 0.14 (0.04 to 0.49) at ≥1:40. The corresponding figures for ages were 0.03 (0.01 to 0.07) for the 0-year-olds and 0.17 (0.08 to 0.34) for the 1-year-olds compared with the 2- to 3-year-olds (Ptrend < 0.001). Similar results were also obtained for the H3 and B strains. Significantly elevated odds ratios for seroprotection were observed with greater prevaccination titers and older ages for all strains. The prevaccination titer and age were independently associated with the antibody response in young children. The immune response was weaker in the younger children and those without preexisting immunity.