Asian Influenza: A Study of 150 Persons During the 1957 Pandemic

In September of 1957, when this study was initiated, numerous questions had arisen concerning the epidemiological and serological characteristics of the new Type A Asian influenza virus and the vaccine developed to combat it. It was decided, therefore, to undertake a study to investigate: (i) the attack rate in a vaccinated as compared to that in an unvaccinated group living in the same community; (ii) the characteristics of the epidemic in a third group, a relatively isolated, unvaccinated population; (iii) the incidence of subclinical infections in the two unvaccinated groups; and (iv) the serological response of individuals to vaccination and to infection as determined by the hemagglutination-inhibition (HI) test and the complement-fixation (CF) test. To study these questions three groups of about 50 subjects each were chosen and followed for a three-month period which included the entire duration of the autumn epidemic. The first study population was composed of individuals given two injections of commercially prepared, monovalent vaccine before the epidemic, the second was an unvaccinated group chosen from the same community, and the third was composed of unvaccinated, institutionalized individuals. Paired blood samples were obtained from all participants. In the vaccinated group an initial sample was taken before the epidemic and another after the second injection of vaccine. Similarly, in the two unvaccinated groups a sample was drawn at the beginning of the study and another was taken at the end of the study from those who remained symptom-free. A sample was drawn after the acute phase of illness from all persons reporting symptoms of influenza.