To the Editor: Rabies vaccine is recommended for pre-exposure prophylaxis in travellers over 1 year old who intend to travel to predominantly developing countries where canine rabies is endemic. The incidence of dog bites in such countries is relatively high, being more common among travellers than typhoid fever.1 Postexposure rabies treatment of pre-immunised travellers is simpler, cheaper and safer than treatment of those who have not been immunised.

Rabies vaccines currently available in Australia are given intramuscularly as three doses of 1.0 mL on Days 0, 7, and 21–28, but are relatively expensive at more than $100 per dose. Some travellers will choose not to be vaccinated because of this cost. For at-risk travellers who might choose to decline vaccination because of the cost, and to facilitate use of pre-exposure vaccination in poorer countries, the World Health Organization approves the intradermal route of vaccination, where 0.1 mL of vaccine is administered, also on Days 0, 7 and 21–28.2

However, the intradermal technique is technically more difficult, may result in lower antibody levels that decline more quickly, and may be interfered with by concurrent administration of chloroquine or immunosuppressants. The Australian immunisation handbook therefore recommends that this technique be performed by vaccinators experienced in the technique, and that satisfactory antibody production is confirmed after vaccination.3 Antibody levels of at least 0.5 IU/mL are considered protective, and the commercial enzyme immunoassay, available under Medicare, has been shown to correlate well with the gold-standard virus neutralisation test.4

We have been using the intradermal method for over 10 years for travellers considered at high risk, but who decline vaccine on cost alone; we use imported human diploid cell vaccine of potency of at least 2.5 IU/mL. As several travellers can be vaccinated from the same vial, costs are $30–$40 per dose, and vials can be stored and reused within 7 days under aseptic conditions. However, travellers must be vaccinated 7–8 weeks before departure to enable antibody testing and a booster vaccination if required.

Recent analysis of 1532 non-immunosuppressed travellers (aged between 9 and 77 years; 55% female) who received three intradermal doses of 0.1 mL rabies vaccine on Days 0, 7, and 21–28 in our Melbourne clinic showed that only seven (0.46%) failed to reach the protective antibody level of 0.5 IU/mL on testing 2–4 weeks after the third dose, with readings of 0.4 IU/mL (in four), 0.3 IU/mL (in two) and 0.2 IU/mL (in one). None had undetectable antibody levels. All seven were advised to receive an intramuscular booster dose of 1.0 mL.

These data support the contention that the intradermal method is appropriate for use in travellers who may otherwise decline pre-exposure rabies vaccination, when the vaccine is administered by vaccinators with relevant experience.5

Recipients of intradermal rabies vaccine who have satisfactory antibody levels may be considered fully vaccinated in the postexposure situation and managed accordingly.