1.         Full name of discloser

The Vanguard Group, Inc.

2.         Owner or controller of interests and short positions disclosed, if different from 1(a)

The naming of nominee or vehicle companies is insufficient. For a trust, the trustee(s), settlor and beneficiaries must be named.

3.         Name of offeror/offeree in relation to whose relevant securities this form relates

Use a separate form for each offeror/offeree

Horizon Therapeutics plc

4.         If an exempt fund manager connected with an offeror/offeree, state this and specify identity of offeror/offeree (Note 1)

5.         Date position held/dealing undertaken

For an opening position disclosure, state the latest practicable date prior to the disclosure

28 April 2023

6.           In addition to the company in 1(c) above, is the discloser also making disclosures in respect of any other party to the offer?

If it is a cash offer or possible cash offer, state “N/A”

N/A

Class of relevant security
(Note 3)

US$0.0001 ordinary shares

Interests

Short positions

Number

%

Number

%

1. Relevant securities owned and/or controlled

21,583,473

9.43%

2. Cash-settled derivatives

3. Stock-settled derivatives (including options) and agreements to purchase/ sell

Total

21,583,473

9.43%

Class of
relevant
security

Product
description
e.g. CFD

Nature of dealing
e.g. opening/ closing a long/ short position, increasing/ reducing a long/ short position

Number of
reference
securities
(Note 6)

Price
per unit
(Note 5)

Class of
relevant
security

Product
description e.g. call
option

Writing, purchasing, selling, varying
etc.

Number
of
securities
to which
option
relates
(Note 6)

Exercise
price per
unit

Type
e.g.
American,
European
etc.

Expiry
date

Option
money
paid/
received per unit

Class of
relevant
security

Product
description
e.g. call
option

Exercising/
exercised
against

Number of
securities

Exercise
price per
unit
(Note 5)

Class of
relevant
security

Nature of dealing
e.g. subscription,
conversion, exercise

Details

Price per unit (if
applicable)
(Note 5)

 Not Applicable

Details of any indemnity or option arrangement, or any agreement or understanding, formal or informal, relating to relevant securities which may be an inducement to deal or refrain from dealing entered into by the person making the disclosure and any party to the offer or any person acting in concert with a party to the offer.

Irrevocable commitments and letters of intent should not be included. If there are no such agreements, arrangements or understandings, state “none”

 none

Full details of any agreement, arrangement or understanding between the person disclosing and any other person relating to the voting rights of any relevant securities under any option referred to on this form or relating to the voting rights or future acquisition or disposal of any relevant securities to which any derivative referred to on this form is referenced. If none, this should be stated.

 none