Smallpox vaccination by intradermal jet injection. 3. Evaluation in a well-vaccinated population.

Smallpox vaccinations were performed in a well-vaccinated prison population by multiple-pressure technique and by intradermal jet injection using serial dilutions of vaccine. A total of 140 subjects were divided into groups, and each group was vaccinated by the multiple-pressure technique or by jet injection using 1 of 3 vaccine dilutions with the following calculated titres: ID-Jet 1 = 10(7.0) TCID(50)/ml, ID-Jet 1a = 10(6.3) TCID(50)/ml, ID-Jet 2 = 10(6.0) TCID(50)/ml. Clinical observations were made at intervals during the first week after vaccination. Prevaccination and post-vaccination serum samples were obtained immediately before and 30 days after the vaccination. Results based on clinical and serological evaluations indicated that smallpox vaccination by jet injection with the ID-Jet 1 vaccine was at least as efficacious as vaccination by the standard multiple-pressure technique.