Immunogenicity of purified duck embryo rabies vaccine (Lyssavac-N) with use of the WHO-approved intradermal postexposure regimen.

The World Health Organization (WHO) has recommended the following regimen for administration of intradermal postexposure rabies vaccines (tissue or avian cultures): 0.1 mL of the vaccine given intradermally at two sites on days 0, 3, and 7 and at one site on days 28 and 90. WHO did not specify which types of vaccines should be used when following this regimen. We evaluated the efficacy of purified duck embryo rabies vaccine (Lyssavac-N) under the above regimen conditions; although purified duck embryo rabies vaccine is highly immunogenic when given intramuscularly, it differs significantly from the other rabies vaccination products in that it is not a solution, but rather, a suspension with an added preservative. Lyssavac-N was found to produce lower mean neutralizing antibody titers with the WHO-recommended intradermal regimen. However, when the volume of each dose was increased from 0.1 mL to 0.2 mL and the same schedule of administration was followed, satisfactory titers were obtained. We concluded that the WHO intradermal postexposure rabies vaccine regimen should only be used with vaccines that have been subjected to immunogenicity studies with satisfactory results.