Intradermal pre-exposure rabies immunisation in New Zealand

Rabies is a fatal infection and immunisation is important to consider in those travellers going to rabies endemic areas. In those at high risk, a course of three immunisations may be given by the intramuscular (IM) or intradermal (ID) route, both of which are approved by the World Health Organization (WHO) and the Centers for Disease Control (CDC). Little is known in the New Zealand context regarding the effectiveness of pre-exposure ID rabies immunisation.

The data was collected prospectively on all travellers requiring the immunisation from July 2001 to September 2003 in Auckland. The standard WHO rabies immunisation protocol was used with three ID injections of 0.1 ml, given on days 0, 7, and 21 or 28 with a booster after 12 months. The vaccine used was the Pasteur Merieux human diploid cell vaccine (HDCV) or the Rabipur Purified chick embryo cell (PCEC) vaccine. Both vaccines are approved by the WHO and the CDC, and are interchangeable. Serology was performed approximately 2 weeks after completion of the primary immunisation course or after a booster, wherever possible. Antibody levels were measured using EIA, and levels of >0.5 IU/ml were considered protective.

Of the 263 travellers assessed in this study, 125 were males and 138 were females. The mean age of the cohort was 34.8 years (SD=11.7). There were not found to be any statistically significant correlations between age and antibody levels neither was there any significant association between gender and antibody levels. In addition to the sample group, a further 12 travellers had rabies serology performed but were excluded from the study because they had IM vaccines as part of their primary course. Whilst rabies serology ranged from 0.2 to 27.9 IU/ml in the study cohort, the mean antibody level for the group was 4.7 IU/ml (SD=4.1 IU/ml). The mean antibody level for males was 4.3 IU/ml (SD=3.3), and for females, 5.2 IU/ml (SD=4.6). Of the 263 travellers, all had some level of detectable antibodies. The overall seroconversion rate was 95.1%.

ID rabies immunisation appears effective, when given according to the standard WHO protocol, in New Zealand. ID rabies immunisation is also more affordable for travellers, especially those on a restrictive budget. ID rabies immunisation can continue to be recommended, particularly where follow-up serology can be done before travel and where there are staff who are experienced in ID immunisation.