A Study of JNJ-64304500 in Participants With Alopecia Areata

Inclusion Criteria

• •Participant has a physician confirmed diagnosis of moderate to severe Alopecia Areata (AA) (greater than or equal to \[\>=\] 50 percent \[%\] scalp involvement) as measured using the severity of Alopecia tool (SALT) score; or participant has \>=95% loss of scalp hair for enrollment as alopecia totalis (AT) or alopecia universalis (AU) subtypes at the time of screening and baseline
• •Current episode of hair loss is greater than (\>) 6 months (without evidence of spontaneous terminal hair regrowth within 6 months at the time of screening and baseline), but less than or equal to (\<=8) years
• •Medically stable on the basis of physical examination, medical history, vital signs, and 12-lead electrocardiogram (ECG) performed at either screening or Week 0. Any abnormalities, must be consistent with the underlying illness in the study population and this determination must be recorded in the participant's source documents and initialed by the investigator
• •Medically stable on the basis of clinical laboratory tests performed at screening. If the results of the serum chemistry panel or hematology are outside the normal reference ranges, the participant may be included only if the investigator judges the abnormalities or deviations from normal to be not clinically significant or to be appropriate and reasonable for the population under study. This determination must be recorded in the participant's source documents and initialed by the investigator