LEUKOPENIA is a characteristic sign of many viral infections and the blood picture in measles is typical of this effect. The leukopenia of natural measles has been the subject of many publications,1-3 but the pattern of changes has been blurred by the absence of precise information on the time and amount of infecting virus and confounded with changes associated with response to secondary bacterial infections. In general, however, it has been shown that the numbers of all major cell types decrease during the prodromal period. Lymphocytes recover somewhat sooner than neutrophils, giving rise to a relative lymphocytosis during the period of rash, the time at which most studies have been made. There have been various and conflicting reports of periods of absolute leukocytosis, but most writers suggest that a slight leukocytosis occurs during the incubation period.
The clinical reaction elicited by live Edmonston measles vaccine mimics a mild case
Black FL, Sheridan SR. Blood Leukocyte Response to Live Measles Vaccine. Am J Dis Child. 1967;113(3):301-304. doi:10.1001/archpedi.1967.02090180061002