The measles (MeV) paradox refers to an apparent contradiction: natural measles causes a transient but profound immune suppression putting patients at risk for opportunistic infections for years, while at the same time MeV infection induces robust immune activation leading to lifelong protection against measles. In this protocol, we test our hypothesis that natural measles causes immune amnesia by altering the composition of circulating immune memory cells. In comparison to the prior studies performed during the 2013 outbreak, we will specifically determine \[1\] to what extent pre-existing immunity is reduced, \[2\] for how long this functional immune suppression can be detected, and \[3\] to what extent MeV-specific immune cells expand. Recently, the WHO reported a 30-fold increase of the number of measles cases in the European Region in 2023 and the ECDC has published a threat assessment brief on increase of the number of cases and considerations for public health response. Combined with the reported drop in vaccination coverage, and several clusters of cases, we anticipate that we are at the verge of a new measles outbreak in the Netherlands