Purified Duck embryo vaccine (PDEV) was the first vaccine developed for human use in treating pre- and postexposure to the rabies virus. It was developed in 1957 and was made of dried, killed rabies virus. Vaccination with DEV involved a series of intradermal injections over several days. The World Health Organization still includes DEV in its list of recommended vaccines for treatment of rabies virus exposure. However, newer vaccines are more commonly used. These include the human diploid cell vaccine (HDCV) first introduced in 1978; purified chicken embyro cell vaccine (PCECV), developed in 1984; and a purified Vero cell rabies vaccine (PVCRV) developed in 1986.