Role of interferon in prophylaxis of rabies after exposure

Rhesus monkeys were completely protected from rabies by a single dose of experimental, highly concentrated, rabies virus vaccine prepared from virus propagated in cultures of human diploid cells and administered several hours after infection with street rabies virus. Protection seemed to be related to the high antigenicity of the vaccine and to its ability to induce interferon in vaccinated animals. Only partial protection was afforded by one or three inoculations of less concentrated vaccines that were prepared from cultures of human diploid cells or primary hamster kidney cells and that were not capable of inducing interferon. The level of virus-neutralizing antibody induced by vaccination could not be correlated with the final outcome of the disease. The simultaneous inoculation of vaccine and interferon inducers (polyribocytidylic acid homopolymer pair or Newcastle disease virus) did not improve the results obtained with vaccine along, a fact which indicates that factors other than interferon and antibody may play an important role in the treatment of rabies after exposure.