Recent Studies in Influenza

W ITHIN the past year a number of significant advances have been made as a result of laboratory investigations of epidemics of influenza. A second etiological agent has been discovered. Indirect evidence has been obtained that at least a third causal agent exists. Two new diagnostic technics have been described. In the case of influenza A it has been found that artificially increased antibody levels* are associated with decreased susceptibility to the disease. The possibility that the etiology of influenza was varied has been recognized for some time. Within two years of the discovery of the first influenza virus by Smith, Andrewes, and Laidlaw 1 these investigators recognized that clinical influenza was probably not a single etiological entity.2 Two years later Francis 3 showed that an epidemic of influenza could occur in the absence of demonstrable infection by the virus of the British workers. Additional epidemics of influenza which occurred in 1940 in England4 and this country 5' 6 were also found not to have been associated with what is now termed influenza A virus.7 As is well known, numerous workersin various parts of the world showed during the period 1935-1940 that in many epidemics influenza A virus had been causally related to the disease. During the past year. it was