Fig. 1. HAV antibody titers. Mean (± SEM) anti-HAV titer in mIU/ml before (day 0) and after (days 5–14 and day 28) hepatitis A vaccination in subjects who had either regular sleep on the night after vaccination (thin line, open circles) or were kept awake on this night (thick line, filled circles). *p = .018, for comparison between the effects of sleep and the wakefulness on day 28.