This protocol for post study access allows pediatric participants (2-11 years old at the time of consent) with HAE who have completed study CSL312_3003 (NCT05819775) to continue treatment with CSL312 for routine prevention of HAE attacks. The continuing treatment with the study product will be administered under a Post Study Access program in accordance with the applicable laws and regulations, to be dictated by CSL Behring (Sponsor) and approved by the appropriate local/central Ethics Committees and all other competent authorities required by law, as applicable.

Inclusion Criteria:

• Completion of treatment period in study CSL312_3003 (NCT05819775)
• The participant responded to CSL312 treatment with no or very limited number of HAE attacks during the CSL312_3003 study
• The participant experienced no clinically significant adverse effects associated with CSL312 treatment
• In the opinion of the treating physician, the participant continues to receive benefit from CSL312
• There is no other suitable alternative prophylactic treatment available at the time of consenting into the Post Study Access program

Exclusion Criteria:

• In the opinion of the treating physician, participant may not be compliant with the Protocol requirements
• Participant is 12 years or older at the time of consent
• In the opinion of the treating physician, other study medication of prophylaxis treatment of HAE may benefit the participant more than continuing treatment with CSL312
• Participant who is pregnant, breastfeeding, or not willing to cease breastfeeding