Why children were not initially included in clinical trials?

The burden of COVID-19 is significantly lower in children than in adults; the vast majority of hospitalizations and deaths caused by COVID-19 have occurred in the adult population, in particular elderly people. For these reasons, the development of the vaccines targeting the adult population was the first priority. Once we learned vaccines are safe and efficacious in adult populations, clinical trials were expanded gradually to include youth and children. Clinical trials to test the safety and efficacy of the COVID-19 vaccine in young children underwent a rigorous process, and were required to meet the same standards as for other vaccines such as polio or measles.

Clinical trials designed for children — and pharmaceutical products tested in children — are the only way to develop age-specific, scientifically tested vaccines and treatments for this unique population.