With a good primary prevention programme a number of healthy individuals will never know that they had a narrow escape from disease and maybe even death. Large numbers of individuals participate in such a programme, while only a few of those would have fallen ill without it.
Nevertheless such a population approach often will yield a larger health benefit (on a population level) than an intervention that only aims at the high risk group in the population. That has been called the prevention paradox.
The choice between a population or a high risk approach has prompted lengthy debates in the Netherlands. Epidemiology offers a methodology to estimate the effects of different approaches.
The health impact will be determined by the distribution of exposure in the population and the risk function of exposure.
In the final decision on a prevention strategy other considerations such as cost-effectiveness of interventions, negative side effects, possibilities of identification of high risk groups and ethical issues can play a part.