The main goal of the study is to assess the long-term safety of eptinezumab on children and adolescents ages 6 to 17 with chronic or episodic migraine.

This is an extension study for participants aged 6 to 17 with migraine who completed either studies 19356A (NCT04965675) (chronic migraine [CM] study in adolescents) or 19357A (episodic migraine [EM] study in children and adolescents). All participants who complete the Week 12 visit of the respective lead-in study will be offered participation in this open-label extension (OLE) study, unless there is a safety concern precluding a participant's participation in the study. Participants originally randomized to 100 milligrams (mg) (weight adjusted) in the double-blind lead-in study (Study 19356A or Study 19357A) will continue on the same dose (100 mg, weight adjusted) in the OLE study. Participants randomized to the 300 mg dose (weight adjusted) in the double-blind lead-in study will continue on 300 mg (weight adjusted) in the OLE study. Participants who were assigned to placebo in the double-blind lead-in study will be randomly allocated to one of the two treatment groups: eptinezumab 100 mg (weight adjusted) or eptinezumab 300 mg (weight adjusted) with a ratio of 1:1.

Inclusion Criteria:

- The participant must have completed Week12 (completion) visit of either Study19356A (CM) or Study19357A (EM) immediately prior to enrolment into this OLE study.

Exclusion Criteria:

• The participant has an adverse event or other safety concerns that are deemed related to double-blind treatment received in the lead-in study and is considered a potential safety risk by the investigator.
• During lead-in Study19356A or Study19357A:
• participant experienced ananaphylactic reaction or another severe and/or serious hypersensitivity reaction to the investigational medicinal product (IMP) infusion, as assessed by the investigator
• the participant had a serum alanine aminotransferase (ALT) or aspartate aminotransferase(AST) value >5 times the upper limit of the reference range that was confirmed by testing <2 weeks later.
• the participant had a serum ALT or AST value >3times the upper limit of the reference range and a serum total bilirubin value >2times the upper limit of the reference range.