Intradermal Postexposure Rabies Vaccine Regimens

Sir—Economical intradermal (id) postexposure rabies vaccine regimens were devised 10–15 years ago to make the excellent modern vaccines available to more people in areas where nerve tissue vaccines were used. Plotkin [1] discusses the treatment regimens and states that the id dose is 0.1 or 0.2 mL per site, depending on the brand of vaccine used. The data in table 4 of Plotkin's article apparently confirmed that this applied to the 8-site regimen, but the statement applies only to the 2-site regimen. Four rabies vaccines are recommended by the World Health Organization (WHO) for id use [2]. The 8-site id regimen (see table 1 here) was initially tested when human diploid-cell vaccine (Imovax rabies; Aventis Pasteur, Lyon, France) was the only tissue-culture vaccine available [3], but it can also be used with purified chick embryo cell vaccine (Rabipur/RabAvert; Chiron Behring, Marburg, Germany) [4] and purified duck embryo vaccine (Lyssavac-N; Berna, Bern, Switzerland), because the volume of vaccine in 1 ampoule is 1.0 mL. The other reco-mmended vaccine, purified Vero cell vaccine (PVRV; Verorab; Aventis Pasteur), has only 0.5 mL per ampoule and it has not been tested with the 8-site regimen. If it were, the logical dose would be 0.05 mL per site. The 2-site id regimen (see table 1 here) was designed for use with PVRV [5]. It requires a dose of 0.1 mL per site for PVRV and a dose of 0.2 mL per site for the other 3 vaccines. Both of these regimens use a similar total amount (<2 ampoules) of vaccine per course of treatment. There are several advantages to use of the 8-site method. First, rapid induction of neutralizing antibody makes the 8-site method the treatment of choice when no rabies immunoglobulin is used (which is the case for >90% of postexposure treatments in Third World countries). Second, there is a wide margin of safety, because (a) if up to half of the 8 id injections on day 0 are not truly id injections, then the immune response will still be adequate [4], and (b) use of a whole ampoule on day 0 avoids the need to share ampoules of vaccine between patients during emergency treatment and also eliminates any risk of contaminating or wasting vaccine. Third, administration of a large antigenic stimulus on day 0 gives the best chance of survival to those patients who are “low responders” [6] to the vaccine and to those who fail to return on time for subsequent doses (a common problem in areas in the rural tropics). The complexity of these treatments demonstrates the urgent need for an improved, simplified single regimen that is suitable for use with all WHO-recommended vaccines. Efforts are being made to establish such a regimen. Meanwhile, there is reluctance to use these vaccines economically. This deprives many patients of excellent treatment and perpetuates double standards of treatment in the Third World. The use of rabies vaccines of nerve tissue origin (Semple and suckling mouse brain vaccines) would be considered unethical in the United States today, but these obsolete vaccines are still given to millions of individuals in other parts of the world each year. Economical intradermal (id) postexposure rabies treatment regimens, compared with the standard im schedule.