# German Million Children Cohort: a historical birth cohort based on claims data to investigate the impact of immunisation and other early life factors on the risk of cancer and other diseases in childhood – cohort profile

## TL;DR

This study uses a large historical dataset of children in Germany to explore how early life factors like vaccinations affect childhood cancer and other diseases.

## Contribution

The German Million Children Cohort is a new historical register-based cohort using claims data to study the long-term health effects of early life factors.

## Key findings

- The cohort includes 2,023,613 children with 3,410 childhood cancer cases identified.
- 38.9% of children received all recommended vaccines by age 30 months.
- The cohort allows for future studies on the impact of the COVID-19 pandemic on child health.

## Abstract

As a historical register-based birth cohort, the German Million Children Cohort was set up using data from the German Pharmacoepidemiological Research Database (GePaRD), a health insurance database covering ~20% of the German population. The first cohort project aims to investigate the impact of Prenatal and Childhood Immunization and the Risk of Childhood Cancer project.

The cohort includes all newborns in GePaRD from 2004 to 2018 and is followed until occurrence of childhood cancer, death, the end of continuous insurance or currently available data years (31 December 2022). Information on vaccinations and confounders is collected from the inpatient and outpatient settings. For most children, information on vaccination exposure during pregnancy can be obtained through mother-child linkage.

The cohort includes 2 023 613 children with a maximum follow-up of 18 years. This results in 17 752 995 person-years at risk and 3410 cases of childhood cancer. Maternal linkage was possible for 78.3% of children. The vaccination coverage for both nationally recommended and other vaccines was assessed in the cohort. By age 30 months, 38.9% of children received all recommended vaccines, 52.4% received incomplete vaccinations and 8.8% remained unvaccinated. Regarding further characteristics, 57.6% of children were from families with higher education, 20.3% were hospitalised due to a severe infection during follow-up and 74.5% received at least one antibiotic prescription.

While our first study with this historical cohort is dedicated to the question of whether immunity to childhood infections that are covered by the recommended baseline vaccination scheme reduces the risk of childhood cancer, the cohort will offer further opportunities. This includes the evaluation of additional factors potentially influencing the risk of cancer and other diseases in childhood, as well as an extension of the inclusion period beyond 2018 to also include children born during the COVID-19 pandemic.