These comments begin with the main ethical or value judgments built into the quantitative model that the committee developed and employed.

The quality-adjusted life year (QALY) has been widely used in health care and other contexts in recent years to compare the outcomes of different health or other interventions. The calculation of QALYs is described in Chapters 4 and 5. The QALY measures the impact an illness or a health intervention on an individuals’ expected years of life and their quality of life. The QALY measure assumes that an additional year of life has the same value regardless of the age of the person who receives it, assuming the life years are of comparable quality; for example, assuming no difference in quality, an additional life year secured for an infant, a 30-year-old, and a 75-year-old all have equal value. In this respect, all QALYs have equal value no matter who receives them or how old individuals are when they receive them.

Recently, a measure of the burden of illness in terms of disability-adjusted life years (DALYs) was developed for the World Bank and World Health Organization (Murray and Lopez, 1996). In contrast to QALYs, DALYs assign different values to years of life depending on age, and independent of differences in health-related quality of life. Roughly, DALYs assign relatively low value to a year of life in infancy and childhood, significantly greater value in the economically productive young adult years, and less value again at older ages. The principal rationale offered for this difference in the social value of life extension based on age was that it is common in many countries for persons to fill different social roles at different ages. In particular, because both the young and the old tend to depend on adults in their productive years for their well-being, the social value of life extension during adult life, as opposed to childhood and old age, was deemed greater.

The committee chose QALYs rather than DALYs because it believes the proper societal perspective on the value of extending its members’ lives focuses on the value to those individuals of extending their lives, not the value of those lives to others. Using the latter perspective would bring in other differentiations between individuals in their social and economic value to others that the committee believes should not be given ethical significance in health care resource allocation in general, or vaccine development priorities in particular.