The concept of vaccination failure.

Despite remarkable success of immunization programmes on a global perspective, vaccines are neither 100% efficacious nor 100% effective. Therefore, vaccination failure, i.e. occurrence of a specific disease in an individual despite previous vaccination, may occur. Vaccination failure may be due to actual vaccine failure or failure to vaccinate appropriately. Universally accepted concepts and definitions of vaccination failure are required to assess and compare the benefit of vaccines used in populations. Here we propose general definitions for types of vaccination failure. In the future, these should be complemented by specific definitions for specific vaccines as needed depending on public health considerations.

Use of prevalence and incidence measures to describe age-related prescribing of antidepressants with and without anticholinergic effects.

To evaluate whether physicians avoid prescribing highly anticholinergic antidepressants (AAD) in the elderly, a population-based retrospectively data analysis was performed using databases from a Dutch health insurance company. Data collected on approximately 240,000 persons covered the period from 1 July 1993 to 1 January 1996. The prevalence and the incidence (number of new starters) of antidepressant use was measured over 1994 and 1995. Use of AAD was proportionally higher in the elderly in terms of both prevalence and incidence rates; the ratio of starters of AAD versus starters of non-AAD in 1994 increased steadily with age (from 0.54 in the age group 20-29 to 1.15 in the age group 60-69). In 1995 these incidence ratios decreased (0.41 to 0.99, respectively); however, the decrease was higher in the younger age groups. The data indicate that in the population studied, physicians do not refrain from prescribing highly anticholinergic agents to older patients despite their potential adverse drug reactions in this age group. This study also indicates that prevalence and incidence rates can be extracted from reimbursement data and give insight into actual prescribing practices.