A 6 year old child, no symptoms - counts returned to normal within 2 weeks. No problems since.
Lymphocytes in this case highly pleomorphic but morphologically unremarkable - subtyping revealed 65% CD3+, 40% CD3+/CD4+, 22% CD3+/CD8+, 30% CD19+ and the remainder CD3-/CD16+/CD56+.
The above pattern of general subset increase has also commonly been seen in splenectomised children, although apparently not reversible.
It is interesting to speculate on the "reactive lymphocytosis" being a mobilisation to the periphery of a "pool" of non-venous lymphocytes due to some unknown stimulus, often sub-clinical.