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The safety, reactogenicity, immunogenicity, and efficacy of the mRNA-1273 coronavirus disease 2019 (Covid-19) vaccine in young children are unknown.Part 1 of this ongoing phase 2-3 trial was open label for dose selection; part 2 was an observer-blinded, placebo-controlled evaluation of the selected dose. In part 2, we randomly assigned young children (6 months to 5 years of age) in a 3:1 ratio to receive two 25-μg injections of mRNA-1273 or placebo, administered 28 days apart. The primary objectives were to evaluate the safety and reactogenicity of the vaccine and to determine whether the immune response in these children was noninferior to that in young adults (18 to 25 years of age) in a related phase 3 trial. Secondary objectives were to determine the incidences of Covid-19 and severe acute respiratory syndrome coronavirus 2 infection after administration of mRNA-1273 or placebo.On the basis of safety and immunogenicity results in part 1 of the trial, the 25-μg dose was evaluated in part 2. In part 2, 3040 children 2 to 5 years of age and 1762 children 6 to 23 months of age were randomly assigned to receive two 25-μg injections of mRNA-1273; 1008 children 2 to 5 years of age and 593 children 6 to 23 months of age were randomly assigned to receive placebo. The median duration of follow-up after the second injection was 71 days in the 2-to-5-year-old cohort and 68 days in the 6-to-23-month-old cohort. Adverse events were mainly low-grade and transient, and no new safety concerns were identified. At day 57, neutralizing antibody geometric mean concentrations were 1410 (95% confidence interval [CI], 1272 to 1563) among 2-to-5-year-olds and 1781 (95% CI, 1616 to 1962) among 6-to-23-month-olds, as compared with 1391 (95% CI, 1263 to 1531) among young adults, who had received 100-μg injections of mRNA-1273, findings that met the noninferiority criteria for immune responses for both age cohorts. The estimated vaccine efficacy against Covid-19 was 36.8% (95% CI, 12.5 to 54.0) among 2-to-5-year-olds and 50.6% (95% CI, 21.4 to 68.6) among 6-to-23-month-olds, at a time when B.1.1.529 (omicron) was the predominant circulating variant.Two 25-μg doses of the mRNA-1273 vaccine were found to be safe in children 6 months to 5 years of age and elicited immune responses that were noninferior to those in young adults. (Funded by the Biomedical Advanced Research and Development Authority and National Institute of Allergy and Infectious Diseases; KidCOVE ClinicalTrials.gov number, NCT04796896.).

Objective Outdoor free play is important for preschoolers' physical activity, health, and development. Certain temperamental characteristics are associated with obesity, nutrition, and sedentary behaviors in preschoolers, but the relationship between temperament and outdoor play has not been examined. This study examined whether there is an association between temperament and outdoor play in young children. Methods Healthy children aged 1 to 5 years recruited to The Applied Research Group for Kids (TARGet Kids!), a community-based primary care research network, from July 2008 to September 2013 were included. Parent-reported child temperament was assessed using the Childhood Behavior Questionnaire. Outdoor free play and other potential confounding variables were assessed through validated questionnaires. Multivariable linear regression was used to determine the association between temperament and outdoor play, adjusted for potential confounders. Results There were 3393 children with data on outdoor play. The association between negative affectivity and outdoor play was moderated by sex; in boys, for every 1-point increase in negative affectivity score, mean outdoor play decreased by 4.7 minutes per day. There was no significant association in girls. Surgency was associated with outdoor play; for every 1-point increase in surgency/extraversion, outdoor play increased by 4.6 minutes per day. Conclusions Young children's temperamental characteristics were associated with their participation in outdoor free play. Consideration of temperament could enhance interventions and strategies to increase outdoor play in young children. Longitudinal studies are needed to elucidate the relationship between children's early temperament and physical activity.

Several studies have suggested an association between vitamin D in childhood and autism spectrum disorder. No prospective studies have evaluated whether lower vitamin D levels precede ASD diagnoses – a necessary condition for causality. The objective of this study was to prospectively evaluate whether vitamin D serum levels in early childhood was associated with incident physician diagnosed ASD. A prospective cohort study was conducted using data from preschool-aged children in the TARGet Kids! practice-based research network in Toronto, Canada, from June 2008 to July 2015. 25-hydroxyvitamin D concentration was measured through blood samples and vitamin D supplementation from parent report. Autism spectrum disorder diagnosis was determined from medical records at follow-up visits. Covariates included age, sex, family history of autism spectrum disorder, maternal ethnicity, and neighborhood household income. Unadjusted and adjusted relative risks and 95% confidence intervals were estimated using Poisson regression with a robust error variance. In this study, 3852 children were included. Autism spectrum disorder diagnosis was identified in 41 children (incidence = 1.1%) over the observation period (average follow-up time = 2.5 years). An association between 25-hydroxyvitamin D concentration and autism spectrum disorder was not identified in the unadjusted (relative risk = 1.04, 95% confidence interval: 0.97, 1.11 per 10 nmol/L increase in 25-hydroxyvitamin D concentration) or adjusted models (adjusted relative risk = 1.06; 95% confidence interval: 0.95, 1.18). An association between vitamin D supplementation in early childhood and autism spectrum disorder was also not identified (adjusted relative risk = 0.86, 95% confidence interval: 0.46, 1.62). Vitamin D in early childhood may not be associated with incident physician diagnoses of autism spectrum disorder.

Supplemental material, AUT756787_Lay_Abstract for Prospective cohort study of vitamin D and autism spectrum disorder diagnoses in early childhood by Yamna Ali, Laura N Anderson, Sharon Smile, Yang Chen, Cornelia M Borkhoff, Christine Koroshegyi, Gerald Lebovic, Patricia C Parkin, Catherine S Birken, Peter Szatmari and Jonathon L Maguire; on behalf of the TARGet Kids! Collaboration in Autism

Objective To evaluate the association between breastfeeding duration and early childhood cardiometabolic risk. Study design A cross-sectional study of 1539 healthy children, 3-6 years of age, recruited through The Applied Research Group for Kids! practice-based research network between October 2009 and August 2015. Adjusted multivariable linear regression was used to examine the association between breastfeeding duration and cardiometabolic risk z score and individual cardiometabolic risk factors of waist circumference, systolic blood pressure, glucose, high-density lipoprotein cholesterol, and triglycerides. Results The mean breastfeeding duration was 12.5 months (SD = 8.4). Breastfeeding duration was associated with lower cardiometabolic risk z score (beta = −0.03; 95% CI −0.05, −0.01). In analysis of cardiometabolic risk factors, each additional 3 months of breastfeeding was associated with a 0.13 cm (95% CI −0.20, −0.05) lower waist circumference and 0.16 mm Hg (95% CI −0.30, −0.02) lower systolic blood pressure. Compared with children who breastfed for 6-12 months, those who breastfed for 12-24 months had a lower systolic blood pressure of 1.07 mm Hg (95% CI −2.04, −0.10). There was no association between breastfeeding duration and cardiometabolic risk for those who breastfed beyond 24 months. Conclusions Breastfeeding duration is associated with lower cardiometabolic risk, although the magnitude of association is small. Causation cannot be inferred. Breastfeeding beyond 24 months may not have an added benefit for cardiometabolic health.