Intradermal Rabies Vaccination

Synopsis: Children who received intradermal vaccination had lower rabies neutralising antibody levels than children intramuscularly immunized.

Concerned bout the high cost of intramuscular rabies vaccine in developing countries, researchers in Thailand compared intradermal (lower volume and, hence, lower cost) and intramuscular use of purified Vero cell rabies vaccine as pre-exposure prophylaxis in children. Three doses of vaccine were given during a 28 day period to each of 190 children and a booster dose was given a year later. Follow up data were available from 82% of children one year after the primary series and from 62% of children two years following the booster dose. Children who received intradermal vaccination had lower rabies neutralizing antibody levels than children intramuscularly immunized. Nonetheless, “adequate” protective titres were achieved in nearly all (94-100 % at the different times tested) children whether they received intradermal or intramuscular vaccine. Side effects were generally minor and were similar in each treatment group.

Comment by Philip R Fischer, MD

Rabies is still a uniformly fatal illness, and there are more than 50 000 human deaths due to rabies each year. Most fatalities occur in children in Asia, South America and Africa, and exposure to rabid dogs is responsible for more than 99% of human rabies deaths worldwide. Human rabies is almost always associated with an actual bite wound, though other more subtle exposures have been reported. Control of animal rabies depends on vaccination of domestic dogs and elimination of stray dogs. Sadly, however, such control programmes require heavy, ongoing expenditures.

Effective rabies vaccines are available. Pre-exposure vaccination provides significant protection and simplifies the post-exposure therapy by obviating the need for rabies immune globulin following exposure to rabies and by decreasing the number of needed post-exposure vaccine doses to two.

There are still, however, several controversial issues in regard to rabies vaccination. Who should be vaccinated? Which vaccine should be used? By which route should vaccine be administered? Cost is a significant factor in determining responses to these questions, and this study from Thailand is, therefore, helpful in identifying a lower cost means of effectively administering rabies vaccines to masses of children at risk of rabies in areas of limited financial resources.

The decision about whether to vaccinate a travellers depends on several individualized factors: age (more risk in children), planned activity (more risk in veterinary workers and spelunkers), destination (most risk in Latin America and Asia, only a few countries risk free), duration of travel, access during travel to emergent administration of rabies immune globulin and financial resources (as well as local cost of the pre-exposure vaccines varies markedly from place to place). Whether immunized before the exposure, additional treatment is necessary following actual or presumed rabies exposure.

Until recently, there were two rabies vaccines available in the United States, Imovax is a human diploid cell rabies vaccine manufactured by Pasteur Merieux Connaught and has forms approved for intradermal and intramuscular use. Rabies Vaccine Adsorbed, produce by SmithKline Beecham, is available for intramuscular use. The FDA recently approved for marketing a new inactivated rabies vaccine (RabAvert, Chiron Corp) this is grown in primary cultures of chicken fibroblasts. It is the first new vaccine against rabies to be introduced in almost 10 years and has been approved for both pre-exposure prophylaxis and post-exposure vaccination. A purified Vero cell rabies vaccine from Pasteur Merieux Connaught was used in the Thai study but is not currently available in the United States.

Reproduced with acknowledgment to ProMed