Immunogenicity of Simulated PCECV Postexposure Booster Doses 1, 3, and 5 Years after 2-Dose and 3-Dose Primary Rabies Vaccination in Schoolchildren

Objectives. To assess the immunogenicity of intradermal (ID) booster doses of Purified Chick Embryo Cell rabies vaccine (PCECV, Rabipur) administered to Thai schoolchildren one, three and five years after a primary ID pre-exposure (PrEP) vaccination series. Methods. In this follow-up study of a randomized, open-label, phase II clinical trial, two simulated post-exposure booster doses of PCECV were administered on days 0 and 3 intradermally to 703 healthy schoolchildren, one, three or five years after primary vaccination with either two or three ID doses of 0.1？mL PCECV. Blood was drawn immediately before and 7, 14 and 365 days after the first booster dose to determine rabies virus neutralizing antibody (RVNA) concentrations. Results. An anamnestic response of approximately 30-fold increase in RVNA concentrations was demonstrated within 14 days after booster. All children (100%) developed adequate RVNA concentrations above 0.5？IU/mL. No vaccine related serious adverse events were seen in any of the vaccinees. Conclusion. ID rabies PrEP with PCECV is safe and immunogenic in schoolchildren and the anamnestic response to a two booster dose vaccination series was found to be adequate one, three, and five years after a two- or three-dose primary PrEP vaccination series. 1. Introduction Rabies post-exposure prophylaxis (PEP) after an exposure to a rabid animal has been demonstrated to be efficacious using tissue culture vaccines (TCV) including purified chick embryo cell vaccine (PCECV), administered either intramuscularly (IM) or intradermally (ID) [1, 2]. However, human rabies remains a significant health problem in countries of Asia and Africa, where more than 99% of the exposures come from rabies-infected dogs that inhabit rural and urban areas. The vast majority of the estimated 55,000 human deaths that occur worldwide every year occur on these two continents [3, 4], mainly due to lack of awareness that results in delayed, inadequate PEP, or even no PEP administered to patients exposed to rabid animals. A significant number of bite exposures and rabies cases occur in children under 15 years of age [5–8]. It has been reported that in Thailand by the age of 15 years approximately one-third of all children will have experienced a dog bite, indicating the potential risk for children to be exposed to a rabid animal [9]. While PEP clearly saves lives, human rabies cases, especially in children, continue to occur despite the availability of vaccines and biologicals. Almost all of these human rabies cases could have been prevented, and almost all occurred due to