Most of the many vaccines developed since Pasteur's time have been based on the same fundamental principles. These standard vaccines work by using either weakened or killed versions of disease- causing germs to stimulate the body's protective immunity. In the future, researchers and doctors will no doubt continue to base their work on these principles when situations warrant.

However, medical science will also utilize new types of vaccines, some of which are already in limited use or presently under development in laboratories around the world. The new techniques stem from a deeper understanding of the structure of the human body gained in the latter half of the twentieth century. In particular, modern vaccine research is based on recent dis- coveries about the makeup of individual body cells and the chemical processes that occur within the cells. Some researchers are focusing on the...