A model to assess the infection potential of jet injectors used in mass immunisation

Jet injectors are needleless injectors that penetrate skin with high-pressu re fluid. They have potential advantages over needles and syringes in mass immunisation programs, but concerns over their capacity to transfer blood-b orne viruses have been a barrier to acceptance. Hepatitis B infection can t ransmit in 10 pl of blood; detection of such low volumes presents severe di fficulties to such assessments. A model to assess jet injector safety was d eveloped using injection of an inert buffer into calves and assaying the ne xt injector discharge, representing the next dose of vaccine, for blood usi ng a highly sensitive ELISA. Four injectors were tested: two with reusable heads and direct skin contact, one with single-use injector heads and one w here the injector head discharged at a distance from the skin. All injector s tested transmitted significant (over 10 pl) volumes of blood; the volumes and frequency of contamination varied with injector. The source of the con tamination was consistent with contamination by efflux of injected fluid an d blood from the pressurised pocket in tissue that is formed during injecti on. This insight should inform the design of safe jet injectors. (C) 2001 E lsevier Science Ltd. All rights reserved.