Repeated Attacks of Influenza

Abstract

Recent reports 1 , 2 , 3 have established the principle that illnesses which on the basis of their similar clinical symptoms would be classified together as influenza can be caused by antigenically different viruses. The same principle must be taken into account when repeated attacks of influenza occur in an individual; that is, in a person who previously has had influenza a subsequent attack may be due to infection with a virus that is antigenically different from the one responsible for the earlier illness. That examples of that sort do occur will be shown by the results of the following experiments in which samples of serum obtained over a period of 4 to 5 years from persons who had had more than one attack of influenza were tested against two antigenically different viruses, the TM virus 1 , 3 and the PR8 strain of the virus of epidemic influenza. 4

Patient A had 2, and Patient B had 3 attacks of influenza during the period of observation. The serums, which were 14 from each patient, included samples obtained at the time of onset of the symptoms of the illnesses, samples obtained 3 to 4 weeks later, and samples obtained at reasonably regular intervening intervals. In order to make the comparison valid all of the samples from each patient were tested at the same time. Each serum dilution was mixed with an equal volume of a suspension (mouse lung) which contained between 100 and 1000 lethal doses of the respective virus per 0.03 cc, and after incubation at 37°C for 1/2 hour 0.06 cc of the mixture was given intranasally to mice which were under ether anesthesia.