Background: Delayed vaccination is a well-studied and critical public health issue. However, limited studies have explored whether familial factors influence vaccination delay. This study aimed to determine whether family structure and comorbidities affect the refusal or delayed receipt of measles-rubella and varicella vaccines.

Methods: We gathered data on all children from birth to 13 months of age between 2006 and 2020 using vaccination records linked with the administrative healthcare claims data from a Japanese city. Multivariable logistic regression analyses were conducted to examine the association of refusal or delay in receiving the first-dose measles-rubella and varicella vaccines with the following factors: the child’s sex; presence of parents, siblings, and grandparents; parental and grandparental comorbidities; chronic pediatric comorbidities in the child and siblings; and year of vaccination.

Results: We identified a total of 14,241 eligible children. Refusal or delayed receipt of the first-dose measles-rubella vaccine was associated with an adjusted odds ratio of 2.46 (95% confidence interval, 1.86-3.24) for maternal absence and 1.61 (1.44-1.80) for paternal absence. Similarly, the refusal or delay in receiving the first-dose varicella vaccine was associated with an adjusted odds ratio of 2.04 (95% confidence interval, 1.01-4.16) for maternal absence and 1.37 (1.12-1.69) for paternal absence. The presence of siblings and maternal comorbidities were significantly associated with vaccination delays.

Conclusions: The absence of a parent, the presence of siblings, and maternal comorbidities were associated with the refusal or delay in receiving measles-rubella and varicella vaccines. Strategies for vaccine recommendation should therefore consider family structure and maternal comorbidities.

Background: This article aims to introduce the Real World Database—a new clinical database in Japan.

Methods: The Health, Clinic, and Education Information Evaluation Institute and Real World Data Co., Ltd. began developing the Real World Database in 2015. This is an electronic medical record database linked to claims data and discharge abstract data from medical institutions in Japan. The institutions agreed to collect data from 218 medical institutions as of June 2021.

Results: In 2019, 82 medical institutions provided data, which showed that 2,184,666 patients received treatment at medical institutions. There were also 334,437 inpatients with at least one hospital stay and 2,011,628 outpatients with at least one visit. More than 200 laboratory test results were available.

Discussion: This database is a potential data source for producing descriptive studies, comparative effectiveness studies, studies of adverse effects, and prediction studies.

Conclusions: The Real World Database provides an opportunity and strategy to produce real-world evidence for Japan.