The only well-documented documented cases of rabies caused by human-to-human transmission occurred among 8 recipients of transplanted corneas, and recently among three recipients of solid organs (see MMWR article). Guidelines for acceptance of suitable cornea and organ donations, as well as the rarity of human rabies in the United States, reduce this risk. In addition to transmission from cornea and organ transplants, bite and non-bite exposures inflicted by infected humans could theoretically transmit rabies, but no such cases have been documented.
Casual contact, such as touching a person with rabies or contact with non-infectious fluid or tissue (urine, blood, feces) does not constitute an exposure and does not require post-exposure prophylaxis. In addition, contact with someone who is receiving rabies vaccination does not constitute rabies exposure and does not require post-exposure prophylaxis.
For more information on person-to-person transmission of rabies, see: Fekadu, M., Endeshaw, T., Alemu, W., Bogale, Y., Teshager, T., and Olson, J. G. (1996). Possible human-to-human transmission of rabies in Ethiopia. Ethiopia Medical Journal, 34, 123-127.