High CD4/CD45RO+ and CD8/CD45RO+ frequencies in children with vaccine-modified measles.

Background: Despite availability and wide vaccine coverage, measles infections still occur especially in developing countries. An outbreak of measles occurred among previously immunized older Ghanaian children who had milder clinical symptoms with measles-specific IgG antibodies that could have been attributed to secondary vaccine failure, suggesting that the infection was vaccine-modified measles (VMM).

Methods: Two-color immunophenotyping of the peripheral blood mononuclear cells was performed at acute, recovery and convalescence phases for 19 VMM patients (mean age 6.2 +/- 3.5 years) using flow cytometry, and compared with that of 20 healthy, sex- and age-matched controls.

Results: The results showed a significantly higher memory helper (CD4(+)/CD45RO(+)) cell frequency and increased suppressor cell (CD8(+)/CD45R0(+)) frequency in VMM patients compared to healthy controls. There were no complications and all the patients recovered completely.

Conclusions: These findings show that the mild symptoms in patients with VMM may have correlated with the increase of memory T cells, which is in sharp contrast with previous reports on acute measles infection. This may suggest that the intact immunologic memory cells could have been crucial for the resolution of VMM.