The Expanded Programme on Immunization has been increasingly successful in reducing the incidence of vaccine-preventable diseases in developing countries (1), where, unfortunately, a pattern of unsafe injection practices has been observed (2). Simonsen et al. estimated the prevalence of unsafe injections to range from 20% up to at least 50% in these countries. In 20-80% of health centres in sub-Saharan Africa there are insufficient supplies and equipment to guarantee safe injection (3). Incorrect injection practices include reuse of contaminated needles and syringes without sterilization between patients (4); incorrect disposal of used needles and syringes in the community (5); absence of swabbing with alcohol or acetone of the reusable nozzles of needle-free jet injectors between consecutive patients (6); and other unsafe practices, such as changing needles but not syringes between patients (7).
When not properly sterilized, or if contaminated, needles and syringes can produce local abscesses (8, 9) and can transmit bloodborne infections between patients (10, 11). Needlestick injuries can transmit infectious agents from patients to health care workers (12-15), while incorrect disposal can transmit disease to the community as a consequence of both needlestick injuries and improper reuse (3). Hepatitis B virus (HBV) (16) and human immunodeficiency virus (HIV) (17) are two of the most important bloodborne pathogens in terms of prevalence, morbidity, and mortality, especially in many parts of the developing world (4, 18). Complications associated with HBV infection include chronic active hepatitis, cirrhosis of the liver, primary hepatocellular carcinoma, and premature death (16). HIV infection leads to the acquired immunodeficiency syndrome (AIDS), opportunistic infections, and premature death.
It is estimated that humans in health care settings receive each year between 8 and 12 billion parenteral injections, of which about one billion are for vaccines (19). In addition to routine immunizations for children, emergency campaigns in 1996 alone, accounted for the administration of more than 240 million doses of vaccine (20). The plans for global measles control and eradication (21) can be expected to require billions more injections than are currently administered. As the number of vaccine injections increases, it may become increasingly difficult to ensure the safety of every injection, and thus to minimize risk for consequent iatrogenic disease (7).
Since 1997, WHO, the United Nations Children's Fund (UNICEF), and the United Nations Population Fund (UNFPA) have strongly recommended (22-24) the use of "auto-disable" needles and syringes (25) designed to prevent improper reuse. (Originally called "auto-destruct", these syringes were renamed because they still require, proper disposal and destruction by incineration or other means.) The three agencies also agreed on a policy of "bundling", which requires donors of vaccine for developing countries also to supply a corresponding number of auto-disable needles and syringes along with "sharps" collection boxes to permit safe disposal.
The full risks and economic costs of conventional needles and syringes and alternative injection delivery technologies have not been adequately compared. We investigated the risks of iatrogenic disease transmission and the economic costs associated with various such devices for the parenteral administration of vaccines and other medications. Sub-Saharan Africa was selected as the setting for the model, because injection practices there are often unsafe, and severe financial barriers exist for the introduction of newer technologies.
The risk model
Three major categories of transmission of bloodborne infections by injection devices were modelled. First, patient-to-patient transmission can occur when a device is reused without sterilization or when it is incorrectly sterilized and transfers infected blood between patients. …