Summary

Hemagglutination-inhibiting antibody responses with selected Group B arthropod-borne virus antigens were studied following administration of living attenuated 17D strain yellow fever vaccine to human subjects who had (a) no previous Group B arbovirus experience, (b) only 17D strain vaccine previously, (c) previous inapparent natural Japanese encephalitis virus infection and (d) complex Group B arbovirus experience previously. The results indicate the following:

• 1.  Previous homologous or heterologous immunological experience did not suppress the yellow fever HI response to the living vaccine. On the contrary, the response was sometimes enhanced.
• 2.  Heterologous HI responses depended upon the nature of the previous Group B arbovirus experience. (a) Subjects with no prevaccination Group B arbovirus experience developed a limited array of low-titered heterologous antibodies. (b) Subjects previously vaccinated with the 17D strain but with no other Group B arbovirus experience exhibited limited intensification and broadening of heterologous HI antibodies. (c) Subjects who had experienced some other Group B virus infection prior to yellow fever vaccination displayed a broad heterologous antibody response producing at times significantly higher HI antibody titers to other viruses.
• 3.  Subjects with relatively low, but not with high, yellow fever neutralization indices prior to revaccination tended to show a significant increase in neutralizing antibody level in response to the vaccines.