Are flaviviruses again active in Mali?

Using a hemagglutinating yellow fever antigen, a serologic investigation was done on 1237 blood samples collected between 1979 and 1983 in five regions of Mali. The results showed that the percentage of positive reactions (greater than 1:10) was higher in the sera of mothers than in their new borns (24.8 versus 12.4). In young children (6 months to 3 years old) the percentages of positive sera varied between 4.4 and 9.6. The values were much higher for persons between 15 to 70 years (28.3% to 43.7%). The presence of high antibody titers in sera of adults, the occurrence of seroconversion in young children (less than 1:10 to 1:40) are arguments for supposing that yellow fever virus or other flaviviruses were active in Mali in the period of our investigation.