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A series of 16 yellow fever (YF) viruses isolated from mosquitoes, monkeys and humans in different epidemiological contexts in Senegal and The Gambia between 1976 and 1983, was analyzed by T1 RNase oligonucleotide fingerprints of the genomic 32P-labeled RNA, by SDS-polyacrylamide gel electrophoresis of the intracellular virus-specified polypeptides, by peptide mapping of the envelope E glycoprotein and by immunological reactivities with monoclonal antibody fluids (MAF's) against the E glycoprotein. These strains had not been passed in suckling mice and were isolated in Aedes pseudoscutellaris Mos 61 cultured cells. These strains showed no virulence in three-week-old Swiss mice when injected intraperitoneally. Direct comparison of the large T1 RNase-resistant oligonucleotide maps indicated a relative genetic stability (92%-100%). A greater change was observed when these strains were compared with an epidemic YF strain isolated in 1965 with an oligonucleotide fingerprint map sharing 82%-88% similarity. The YF-specified proteins were identical in their molecular weight, and the fragments obtained after limited proteolysis of the envelope protein using protease V8 or alphachymotrypsine indicated that the strains were chemically similar. Only a few differences were observed when the strains were seroneutralized with MAF's, but no relation could be made with genetic or biological data. This suggested that the YF virus strains isolated from the same geographic area and during a short period of time had evolved slowly. Moreover, all the viruses were closely related and no correlation could be established with the apparent variations in virulence in nature.

In most developing countries, hepatitis prevention has to be carried out early in life and on a mass scale. In such countries, mobile immunization teams have a limited number of sessions to devote to each rural community ans simultaneous administration of multiple antigens is normal practice. We have, therefore, compared the immune response to yellow fever and hepatitis B vaccines when injected simultaneously or not to Senegalese children. Injections were done at time of booster injections for hepatitis B vaccine. Yellow fever antibodies were detected in a similar proportion in infants immunized with yellow fever vaccine. However, a lower proportion of high yellow fever antibody levels was observed when the two vaccines were injected simultaneously. No reduction in the anti-HBs anamnestic response was observed when yellow fever vaccine was injected at the same time as the booster dose of hepatitis B vaccine. As no untowards reactions were noted, it can be concluded from the results that hepatitis B vaccine and yellow fever vaccine could be injected at the same time.