I. Foreword-With a Review of the Past Experiences of the Yale Poliomyelitis Study Unit with Oral Poliovirus Vaccines **

Early in 1961 a city-wide oral poliomyelitis vaccination program was under-taken in the city of Middletown, Connecticut by the and his staff. A description of various aspects of this so-called mass vaccination project follows in the papers that make up this issue of THE YALE JOURNAL OF BIOLOGY AND MEDICINE. In the Middletown program some 10,000 children under the age of 18 received oral poliovirus vaccine (Sabin strains) in two doses: the first given in January 1961, consisting of monovalent vaccine containing Type I poliovirus, and the second six weeks later, in March 1961, a bivalent vaccine containing polioviruses types II and III. The study is the culmination of a six-year program concerned with oral poliovirus vaccines in which the Yale Poliomyelitis Study Unit has been engaged since the Sabin attenuated poliovirus strains first became available to us in 1955.t Of the several trials of oral vaccination which this Unit has conducted, this has been the largest we have attempted and one which has benefited from both our own previous experiences and those of others whose reports have been accumulating rapidly during the past two or three years. By and large, the general objective of the Yale Poliomyelitis Study Unit has been to observe and study carefully what happens to a population when some of its members are artificially infected (vaccinated) with attenuated poliovirus strains and others are intimately exposed to individuals so infected. In other words, we have regarded these trials in large part as a setting for work in experimental epidemiology, with the rare opportunity to do freely in man what previously, in the study of other diseases, has been possible only in populations of animals or birds. Thus t We have been indebted to Dr. A. B. Sabin since 1955 for providing us with a generous supply of his vaccine.