Unravelling the Measles Paradox in Children: a Disease Associated With Both Immune Suppression and Immune Activation

Measles is caused by measles virus (MeV). The disease is associated with lymphopenia and immune suppression, which is an important cause of measles-associated morbidity and mortality. Measles-induced immune suppression can last several years, whereas measles lymphopenia is usually resolved within two weeks. At the same time, measles induces lifelong immunity. This apparent contradiction, known as the 'measles paradox', was partially solved when investigators demonstrated that MeV infects and depletes pre-existing memory cells, thereby causing 'immune amnesia'. This model is supported by observations in animal models and clinical studies, but several questions remain to be addressed, like the duration of measles-induced amnesia and changes in the immune repertoire after measles. Recently, investigators have acquired permission to address these remaining questions in 18-25 years old adults (MEC-2024-0230). However, investigators have reservations about the feasibility of including enough participants between 18 and 25 years old that have not been vaccinated against or infected with MeV; it is possible that investigators will not reach sufficient inclusions to address the immunological questions regarding MeV infection in that protocol. Therefore, investigators propose to additionally study these questions in children in the age of 4 up to and including 17.