“…In humans, viral infection or vaccination with attenuated viruses is associated with transient depression in the host immune defenses [11], and this has been clearly demon strated for rubella, herpes simplex, measles, cytomegalo virus and Epstein-Barr virus [9,13,14,19] as well as for influenza [10]. The same phenomenon has been observed after vaccination with attenuated living virus [8,15], This immunosuppression may presumably be responsible for the increased susceptibility to other viruses or other bac terial infections such as can be observed, for example, after measles.…”