Individuals living in the United States experience an average of four or five common cold illnesses each year. Since etiological agents of this syndrome could not be propagated in the laboratory until recently, progress was slow in defining the cause of mild upper respiratory infections and the factors involved in resistance to illness. In the past frequent occurrence of common colds was attributed to rapid loss of immunity or failure of the host to develop immunity. Studies were limited to investigations in which volunteers were challenged with infective nasal washings. Jackson and co-workers, for example, demonstrated that prior infection with a common-cold nasal secretion conferred a significant degree of resistance when volunteers were rechallenged with the same secretion.
Shortly after the introduction of tissue-culture techniques into modern virological research, the first of a large group of viruses responsible for a significant proportion of minor respiratory illness was recovered by Pelon