Vaccination as teenagers against meningococcal disease and the risk of the chronic fatigue syndrome.

The etiology of chronic fatigue syndrome (CFS)/myalgic encephalomyelitis (ME) is unknown. In Norway, a vaccine against Neisseria meningitides group B was administered to teenagers in 1988--1989 in a protection trial. In order to estimate the relative risk of CFS/ME according to vaccine history, we conducted a case-control study in 2007, with 201 cases diagnosed at one of two hospitals and 389 controls.