LONG-TERM PROTECTIVE RABIES ANTIBODIES IN THAI CHILDREN AFTER PRE-EXPOSURE RABIES VACCINATION

Rabies is a viral zoonosis affecting around 16,000-39,000 people annually. Pre-exposure vaccination should be offered to individuals at high risk of rabies exposure and is suggested for children living in rabies endemic areas.The incidence rate of dog bite in the test group was 14.1/1,000 person-years. Intradermal (ID) route of administration is considered an alternative to the standard intramuscular (IM) administration, and reduces vaccination cost. A 3-year clinical study of a rabies vaccine administered IM or ID to 12–18-month-old Thai children, simultaneously with a Japanese encephalitis (JE) vaccine (M49P2 study), revealed that all regimens used elicited an adequate immune response. In order to determine the long-term (4-8 years) rabies neutralizing antibody titers induced by the pre-exposure regimens, blood was collected annually from 68 from the M49P2 study and analyzed using a rapid fluorescence focus inhibition test. Full- IM(three doses of 1 ml/dose), half-IM(three doses of 0.5 ml/dose), and 3-ID(three doses of 0.1 ml/dose) regimens induced antibody titers above the seroprotective level throughout the study period. However, the 2-ID(two doses of 0.1 ml/dose) group had sub-seroprotective titer of 6.7%, 13.4%, 25.0%, and 36.4% in year 5, 6, 7, and 8, respectively. A secondary immune response was induced by rabies booster vaccination. This study demonstrates a reduced-dose rabies regimen may lower the cost of long-term protection against rabies for vulnerable populations, thus improving the cost-effectiveness of pre-exposure rabies vaccination in children.