This study will assess the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of single ascending doses (SADs) of ALXN1920 subcutaneous (SC) and of a single dose of ALXN1920 intravenous (IV) in healthy adult participants.

This is a first-in-human study in healthy adult participants.

Eligible participants will be randomly assigned in a 3:1 (ALXN1920:Placebo) ratio in each of the treatment cohorts. The first 2 participants randomized to each cohort will be dosed as a sentinel pair, with 1 participant on active treatment and 1 participant on placebo. At the discretion of the Investigator, up to 3 more participants will be added at least 48 hours after the dosing of the sentinel pair, followed by dosing of the remaining participants in the cohort no earlier than 72 hours after sentinel pair dosing.

The study will comprise:

A Screening Period of up to 28 days; A Dosing Period (single dose through to Follow-up Visit) of approximately 28 days; A Final Follow-up period and end of study Visit is planned on Day 29.

Each participant will be involved in the study for approximately 56 days.

Inclusion Criteria:

• Healthy participants
• Body mass index within 18.0 to 32.0 kg/m^2 (inclusive), with a minimum body weight of 50.0 kg.
• Female participants of childbearing potential and male participants must follow protocol-specified contraception guidance.
• For Cohort 6, participants of Japanese descent, defined as having both parents and 4 grandparents who are ethnically Japanese.

Exclusion Criteria:

• Significant history or current cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrinological, hematological, or neurological disorders.
• History of significant allergic reaction.
• History of any Neisseria infection
• Active systemic bacterial, viral, or fungal infection.
• Participants who at Day -1 are either testing positive for coronavirus disease 2019 (COVID-19), or have not had at least 4 weeks elapse of recovery time (a negative test), or are experiencing long-term COVID-19-related sequelae.
• Any major surgery within 8 weeks of Screening.
• Known or suspected history of drug or alcohol abuse.
• Current tobacco users or smokers.
• Positive Human immunodeficiency virus (HIV) infection, hepatitis B or hepatitis C viral infection.
• Female participant who are pregnant, breastfeeding, or intending to conceive during the course of the study.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal. All request will be evaluated as per the AZ disclosure commitment: https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA Pharma Data Sharing Principles. For details of our timelines, please refer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the deidentified individual patient-level data in an approved sponsored tool . Signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information. Additionally, all users will need to accept the terms and conditions of the SAS MSE to gain access. For additional details, please review the Disclosure Statements at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.