Conventional preventive vaccines against infectious diseases have been highly effective at reducing drastically the incidence and morbidity of many life-threatening plagues such as smallpox and viral poliomyelitis. Preexposure vaccination is essential for most infectious diseases caused by viruses or bacteria. A single exception is the rabies vaccine, developed by Pasteur more than 100 years ago, which is administered only after exposure to the virus. In this disease, the virus is shown to progress from the distal site through the peripheral viruses to reach the brain. The mechanism for vaccine efficacy is believed to be that of induction of antibody that suppresses viral migration through the nerve axons.1
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1 Sela, Michael, and Hilleman, Maurice R. “Therapeutic vaccines: Realities of today and hopes for tomorrow.” Proceedings of the National Academy of Sciences of the United States of America, vol. 101, suppl. 2:14559, Oct. 5, 2004. The National Center for Biotechnology Information, ncbi.nlm.nih.gov/pmc/articles/PMC522000/.