- Participants in the early Alzheimer's disease (AD) spectrum at time of enrollment under the parent protocol and according to its inclusion and exclusion criteria, must have very recently completed their treatment in a Phase 1b or Phase 2 JNJ-54861911 clinical study (example [e.g.], 54861911ALZ2002) under the parent protocol. Enrollment in this study should be completed (Day 1 of double-blind [DB] treatment phase) as soon as possible, but within 6 weeks, following completion of their treatment period under the parent protocol. If not defined under the parent protocol, completion of the treatment period is defined as having completed all study related procedures of the last visit of the treatment period under the parent protocol. A screening phase of up to 12 weeks may be allowed following written approval of the Sponsor