SUMMARY

        This summary highlights information contained elsewhere in this proxy statement/prospectus and may not contain all of the information that might be important to you. Alexion and AstraZeneca urge you to read carefully the remainder of this proxy statement/prospectus, including the attached annexes, the documents incorporated by reference into this proxy statement/prospectus and the other documents to which Alexion and AstraZeneca have referred you. You may obtain the information incorporated by reference in this proxy statement/prospectus without charge by following the instructions in the section entitled "Where You Can Find Additional Information." Each item in this summary includes a page reference to direct you to a more complete description of the topics presented in this summary.

Information about the Companies (page 107)

AstraZeneca PLC

1 Francis Crick Avenue
Cambridge Biomedical Campus
Cambridge CB2 0AA
England
Tel: +44-20-3749-5000

        AstraZeneca was incorporated in England and Wales on June 17, 1992, under the Companies Act 1985. It is a public limited company domiciled in the UK. AstraZeneca is a global, science-led biopharmaceutical company that focuses on the discovery, development and commercialization of prescription medicines, primarily for the treatment of diseases in three therapy areas—Oncology, Cardiovascular, Renal & Metabolism, and Respiratory & Immunology. Based in Cambridge, UK, AstraZeneca operates in over 100 countries and its innovative medicines are used by millions of patients worldwide. AstraZeneca holds all of the common stock of Bidco, a direct wholly owned subsidiary formed in the State of Delaware for the sole purpose of completing the transaction.

        AstraZeneca is a public company trading on LSE, the Nasdaq Stockholm and Nasdaq under the ticker symbol "AZN." AstraZeneca's principal executive offices are located at 1 Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0AA, England, and its telephone number is +44-20-3749-5000.

        Additional information about AstraZeneca can be found on its website at http://www.AstraZeneca.com. The information contained in, or that can be accessed through, AstraZeneca's website is not intended to be incorporated into this proxy statement/prospectus. For additional information about AstraZeneca, see the section entitled "Where You Can Find Additional Information."

Delta Omega Sub Holdings Inc.
Delta Omega Sub Holdings Inc. 1
Delta Omega Sub Holdings LLC 1

Corporation Trust Company
1209 Orange Street
Wilmington, DE 19801
1-800-677-3394

        Each of Bidco, a Delaware corporation and a direct wholly owned subsidiary of AstraZeneca, Merger Sub I, a Delaware corporation and a direct wholly owned subsidiary of Bidco, and Merger Sub II, a Delaware limited liability company and a direct wholly owned subsidiary of Bidco, were formed solely for the purpose of facilitating the transaction. Neither Bidco nor either Merger Sub has

carried on any activities or operations to date, except for those activities incidental to such entity's formation and undertaken in connection with the transactions contemplated by the merger agreement.

        By operation of the transaction, Merger Sub I will be merged with and into Alexion. As a result, Alexion will survive the first merger as a direct wholly owned subsidiary of Bidco. Upon completion of the first merger, (1) Merger Sub I will cease to exist as a separate entity, and (2) Alexion will thereafter be merged with and into Merger Sub II. As a result, Merger Sub II will survive the second merger as a direct wholly owned subsidiary of Bidco and therefore an indirect wholly owned subsidiary of AstraZeneca. Upon completion of the second merger, Alexion will cease to exist as a separate entity.

        Bidco, Merger Sub I and Merger Sub II's principal executive offices, respectively, are located at Corporation Trust Company, 1209 Orange Street, Wilmington, Delaware 19801, and the telephone number for Bidco and both Merger Subs is 1-800-677-3394.

Alexion Pharmaceuticals, Inc.

121 Seaport Boulevard
Boston, Massachusetts 02210
(475) 230-2596

        Alexion is a Delaware corporation. Alexion is a global biopharmaceutical company focused on serving patients and families affected by rare diseases and devastating conditions through the discovery, development and commercialization of life-changing medicines. As a leader in rare diseases for more than 25 years, Alexion has developed and commercializes two approved complement inhibitors to treat patients with paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), as well as the first and only approved complement inhibitor to treat anti-acetylcholine receptor (AChR) antibody-positive generalized myasthenia gravis (gMG) and neuromyelitis optica spectrum disorder (NMOSD) in patients who are anti-aquaporin-4 (AQP4) antibody positive. Alexion also has two enzyme replacement therapies and the first and only approved therapies for patients with life-threatening and ultra-rare metabolic disorders, hypophosphatasia (HPP) and lysosomal acid lipase deficiency (LAL-D) as well as the first and only approved Factor Xa inhibitor reversal agent.

        In addition to Alexion's marketed therapies, the company has a diverse pipeline resulting from internal innovation and business development. The company is developing several mid-to-late-stage therapies, including a copper-binding agent for Wilson disease, an anti-neonatal Fc receptor (FcRn) antibody for rare Immunoglobulin G (IgG)-mediated diseases and an oral Factor D inhibitor as well as several early-stage therapies, including one for light chain (AL) amyloidosis, a second oral Factor D inhibitor and a third complement inhibitor. Alexion focuses its research efforts on novel molecules and targets in the complement cascade and its development efforts on hematology, nephrology, neurology, metabolic disorders, cardiology, ophthalmology and acute care.

        Alexion is a public company trading on the Nasdaq under the ticker symbol "ALXN." Alexion's principal executive offices are located at 121 Seaport Boulevard, Boston, Massachusetts 02210 and its telephone number is (475) 230-2596.

        Additional information about Alexion can be found on its website at www.alexion.com. The information contained in, or that can be accessed through, Alexion's website is not intended to be incorporated into this proxy statement/prospectus. For additional information about Alexion, see the section entitled "Where You Can Find Additional Information."

Risk Factors (page 29)

        The transaction and an investment in AstraZeneca ADSs or AstraZeneca ordinary shares involve risks, some of which are related to the transaction. In considering the transaction, you should carefully

consider the information about these risks set forth under the section entitled "Risk Factors," together with the other information included or incorporated by reference in this proxy statement/prospectus.

The Transaction and the Merger Agreement (page 109)

        The merger agreement provides that, upon the terms and subject to the conditions set forth in the merger agreement, at the first effective time, (1) Merger Sub I, a direct wholly owned subsidiary of Bidco, will merge with and into Alexion with Alexion surviving as a wholly owned subsidiary of Bidco, and (2) immediately thereafter Alexion will merge with and into Merger Sub II, with Merger Sub II continuing as the surviving company as a direct wholly owned subsidiary of Bidco and therefore an indirect wholly owned subsidiary of AstraZeneca. As a result, Alexion will cease to be a publicly traded company. The terms and conditions of the transaction are contained in the merger agreement, which is described in this proxy statement/prospectus and attached to this proxy statement/prospectus as Annex A. You are encouraged to read the merger agreement carefully, as it is the legal document that governs the transaction. All descriptions in this summary and elsewhere in this proxy statement/prospectus of the terms and conditions of the transaction are qualified by reference to the merger agreement.

Merger Consideration (page 110)

        Upon the terms and subject to the conditions set forth in the merger agreement, each eligible share of Alexion common stock will be converted into the right to receive (1) 2.1243 AstraZeneca ADSs (or, at the election of the holder thereof, a number of ordinary shares of AstraZeneca equal to the number of underlying ordinary shares represented by such AstraZeneca ADSs) and (2) $60.00 in cash. For a full description of the treatment of Alexion Stock Options, Alexion RSU Awards and Alexion PSU Awards, see the sections entitled "The Merger Agreement—Treatment of Alexion Equity Awards" and "The Merger Agreement—Merger Consideration" beginning on pages 111 and 110, respectively.

Ordinary Share Election of the Share Consideration

        The merger consideration includes the share consideration and the cash consideration. With regard to the share consideration, each outstanding eligible share will be converted into the right to receive (a) 2.1243 AstraZeneca ADSs, each of which represents 0.5 AstraZeneca ordinary shares, or (b) if an Alexion stockholder timely elects, 1.06215 AstraZeneca ordinary shares in lieu of such AstraZeneca ADSs described in clause (a). If an Alexion stockholder does not make an ordinary share election, the Alexion stockholder will receive 2.1243 AstraZeneca ADSs for each issued and outstanding share of Alexion common stock.

        For example, if a stockholder owns 100 shares of Alexion common stock, the shareholder will receive, in each case without interest and subject to any applicable withholding taxes, (i) $6,000.00 in cash and (ii) either 212 AstraZeneca ADSs plus cash in lieu of the fractional 0.43 AstraZeneca ADSs otherwise payable or, if the Alexion stockholder makes the ordinary share election, 106 AstraZeneca ordinary shares plus cash in lieu of the fractional 0.215 AstraZeneca ordinary share otherwise payable.

        Each Alexion stockholder of record will be mailed an election form that will allow such Alexion stockholder to make an ordinary share election for all (but not less than all) of their shares of Alexion common stock. If an Alexion stockholder makes the ordinary share election, the AstraZeneca ordinary shares received by such Alexion stockholder will serve as the share consideration.

        To make the ordinary share election, an Alexion stockholder must return a properly completed and signed election form to the exchange agent prior to the election deadline. AstraZeneca and Alexion will communicate to Alexion stockholders prior to closing of the transaction the applicable deadline for making an ordinary share election.

        If the election deadline is delayed, AstraZeneca and Alexion will promptly announce any such delay and, when determined, the rescheduled election deadline.

        Neither AstraZeneca nor Alexion is making any recommendation as to whether Alexion stockholders should make an ordinary share election. You must make your own decision with respect to such ordinary share election.

        For more information, please see the section titled "The Merger Proposal—Merger Consideration—Ordinary Share Election of Share Consideration."

Alexion Board of Directors' Recommendation (page 59)

        The Alexion board of directors unanimously recommends that you vote "FOR" the merger proposal, "FOR" the compensation proposal and "FOR" the adjournment proposal. For a description of some of the factors considered by the Alexion board of directors in reaching its decision to approve the merger agreement and additional information on the recommendation of the Alexion board of directors that Alexion stockholders vote to adopt the merger agreement, see the section entitled "The Merger Proposal—Recommendation of the Alexion Board of Directors; Alexion's Reasons for the Transaction" beginning on page 59.

Comparative Per Share Market Price Information (page 25)

        The following table presents the closing price per AstraZeneca ADS on Nasdaq and the closing price per share of Alexion common stock on Nasdaq on (i) December 11, 2020, the last full trading day prior to the public announcement of the merger agreement, and (ii) April 7, 2021, the last practicable trading day prior to the mailing of this proxy statement/prospectus. This table also shows the implied value of the merger consideration payable for each share of Alexion common stock, which was calculated by multiplying the closing price of AstraZeneca ADSs on Nasdaq on those dates by the exchange ratio and adding the cash consideration.

Date		AstraZeneca ADSs Nasdaq			Alexion common stock Nasdaq			Equivalent value of merger consideration per share of Alexion common stock based on price of AstraZeneca ADSs on Nasdaq
		(US$)			(US$)			(US$)
December 11, 2020			54.27			120.98			175.29
April 7, 2021			48.42			152.35			162.86

Opinion of Alexion's Financial Advisor (page 63)

        On December 11, 2020, at a meeting of the Alexion board of directors held to evaluate the transaction, BofA Securities, Inc. ("BofA Securities"), Alexion's financial advisor, delivered to the Alexion board of directors an oral opinion, which was confirmed by delivery of a written opinion dated December 11, 2020, to the effect that, as of the date of the opinion and based on and subject to various assumptions and limitations described in BofA Securities' written opinion, the merger consideration to be received in the transaction by holders of Alexion common stock was fair, from a financial point of view, to such holders.

        The full text of BofA Securities' written opinion to the Alexion board of directors, which describes, among other things, the assumptions made, procedures followed, factors considered and limitations on the review undertaken, is attached as Annex B to this proxy statement/prospectus and is incorporated by reference herein in its entirety. The summary of BofA Securities' opinion included in this proxy

statement/prospectus is qualified in its entirety by reference to the full text of BofA Securities' written opinion. BofA Securities delivered its opinion to the Alexion board of directors for the benefit and use of the Alexion board of directors (in its capacity as such) in connection with and for purposes of its evaluation of the transaction. BofA Securities' opinion does not address any other terms or other aspects or implications of the proposed transaction and no opinion or view was expressed as to the relative merits of the proposed transaction in comparison to other strategies or transactions that might be available to Alexion or in which Alexion might engage or as to the underlying business decision of Alexion to proceed with or effect the proposed transaction. BofA Securities' opinion does not address any other aspect of the transaction and does not express any opinion or recommendation as to how any stockholder should vote or act in connection with the proposed transaction or any related matter. See the section entitled "The Merger Proposal—Opinion of Alexion's Financial Advisor" beginning on page 63.

The Alexion Special Meeting (page 43)

        The Alexion special meeting will be held virtually via the Internet on May 11, 2021, beginning at 9:00 a.m., Eastern Time. In light of ongoing developments related to the COVID-19 (coronavirus) pandemic, Alexion has elected to hold the Alexion special meeting solely by means of remote communication via the Internet. The Alexion special meeting will be held solely via live webcast and there will not be a physical meeting location. Alexion stockholders will be able to attend the Alexion special meeting online and vote their shares electronically during the meeting by visiting www.virtualshareholdermeeting.com/ALXN2021SM (which we refer to as the "special meeting website").

        The purposes of the Alexion special meeting are as follows:

•

Proposal 1:  Adoption of the Merger Agreement.    To consider and vote on the merger proposal;



•

Proposal 2:  Approval, on an Advisory (Non-Binding) Basis, of Certain Merger-Related Compensatory Arrangements with Alexion's Named Executive Officers.    To consider and vote on the compensation proposal; and



•

Proposal 3:   Adjournment of the Alexion Special Meeting.    To consider and vote on the adjournment proposal.

        Completion of the transaction is conditioned on the approval of the merger proposal by Alexion's stockholders. Neither approval of the compensation proposal nor approval of the adjournment proposal is a condition to the obligation of either Alexion or AstraZeneca to complete the transaction.

        Only holders of record of shares of Alexion common stock outstanding as of the close of business on March 30, 2021, the record date for the Alexion special meeting, are entitled to notice of, and to vote at, the Alexion special meeting or any adjournment or postponement of the Alexion special meeting. Alexion stockholders may cast one vote for each share of Alexion common stock that Alexion stockholders own of record as of that record date.

        A quorum of Alexion stockholders is necessary to hold the Alexion special meeting. A quorum will exist at the Alexion special meeting if holders of record of shares of Alexion common stock representing a majority of the outstanding shares of Alexion common stock entitled to vote at the meeting are present via the special meeting website or represented by proxy. All shares of Alexion common stock represented by a valid proxy and all abstentions will be counted as present for purposes of establishing a quorum. All of the proposals for consideration at the Alexion special meeting are considered "non-routine" matters under the NYSE and Nasdaq rules, and, therefore, brokers are not permitted to vote on any of the matters to be considered at the Alexion special meeting unless they have received instructions from the beneficial owners. As a result, no "broker non-votes" are expected at the meeting, and shares held in "street name" will not be counted as present for the purpose of

determining the existence of a quorum unless the stockholder provides their bank, broker or other nominee with voting instructions for at least one of the proposals brought before the Alexion special meeting.

        Assuming a quorum is present at the Alexion special meeting, approval of the merger proposal requires the affirmative vote of at least a majority of the outstanding shares of Alexion common stock entitled to vote on the proposal. Shares of Alexion common stock not present at the Alexion special meeting, shares that are present and not voted on the merger proposal, including due to the failure of any Alexion stockholder who holds their shares in "street name" through a bank, broker or other nominee to give voting instructions to such bank, broker or other nominee with respect to the merger proposal, and abstentions will have the same effect as a vote "AGAINST" the merger proposal.

        Assuming a quorum is present at the Alexion special meeting, approval of the compensation proposal requires the affirmative vote of at least a majority of the votes cast on the compensation proposal by shares of Alexion common stock present at the special meeting website or represented by proxy at the Alexion special meeting. A failure to vote, a broker non-vote or an abstention will have no effect on the outcome of the compensation proposal, assuming a quorum is present.

Whether or not there is a quorum, the approval of the adjournment proposal requires the affirmative vote of at least a majority of the votes cast on the adjournment proposal by shares of Alexion common stock present at the special meeting website or represented by proxy at the Alexion special meeting. A failure to vote, a broker non-vote or an abstention will have no effect on the outcome of the adjournment proposal.

Listing of AstraZeneca ADSs (page 79)

        The completion of the transaction is conditioned upon the approval for listing of AstraZeneca ADSs issuable pursuant to the merger agreement on Nasdaq, subject to official notice of issuance. In addition, it is a requirement that AstraZeneca receive acknowledgement by the FCA and LSE that the ordinary shares represented by the AstraZeneca ADSs to be issued in connection with the transaction shall be admitted to the premium segment of the FCA's official list and to trading on the LSE's main market for listed securities.

Delisting and Deregistration of Alexion Common Stock (page 79)

        As promptly as practicable after the first effective time, the Alexion common stock currently listed on Nasdaq will cease to be listed on Nasdaq and will be deregistered under the U.S. Exchange Act.

Material U.S. Federal Income Tax Consequences (page 95)

        AstraZeneca and Alexion intend that the steps involved in the transaction, taken together as an integrated transaction, will qualify as a "reorganization" within the meaning of Section 368(a) of the Code and that Section 367(a)(1) of the Code will not apply to cause the transaction to result in gain recognition by Alexion stockholders that exchange their shares of Alexion common stock for the merger consideration (other than any such Alexion stockholder who would be treated as a "five-percent transferee shareholder" (within the meaning of Treasury Regulations Section 1.367(a)-3(c)(5)(ii)) of AstraZeneca following the transaction who does not enter into a five-year gain recognition agreement in the form provided in Treasury Regulations Section 1.367(a)-8). The obligation of Alexion to complete the transaction is conditioned upon the receipt of an opinion from Wachtell, Lipton, Rosen & Katz, special counsel to Alexion, or Freshfields Bruckhaus Deringer US LLP, counsel to AstraZeneca, to the effect that, on the basis of facts, representations and assumptions set forth or referred to in such opinion, the transaction will qualify as a "reorganization" within the meaning of Section 368(a) of the Code and that Section 367(a)(1) of the Code will not apply to cause the transaction to result in gain recognition by Alexion stockholders (other than any such Alexion stockholder who would be treated as

a "five-percent transferee shareholder" (within the meaning of Treasury Regulations Section 1.367(a)-3(c)(5)(ii)) of AstraZeneca following the transaction who does not enter into a five-year gain recognition agreement in the form provided in Treasury Regulations Section 1.367(a)-8).

        Accordingly, on the basis of such opinion that the transaction qualifies as a reorganization and that Section 367(a) does not apply to require gain recognition, and assuming that, in the case of any holder who would be treated as a "five-percent transferee shareholder" (within the meaning of Treasury Regulations Section 1.367(a)-3(c)(5)(ii)) of AstraZeneca following the transaction, such holder enters into a five-year gain recognition agreement in the form provided in Treasury Regulation Section 1.367-8(a), a U.S. Holder that exchanges shares of Alexion common stock for the merger consideration in the transaction will generally recognize gain (but not loss) in an amount equal to the lesser of: (i) the cash consideration (excluding cash received in lieu of fractional AstraZeneca ADSs or AstraZeneca ordinary shares, if any) received by such U.S. Holder in the transaction; and (ii) the excess, if any, of (a) the sum of the cash consideration (excluding cash received in lieu of fractional AstraZeneca ADSs or AstraZeneca ordinary shares, if any) plus the fair market value of the share consideration (including any fractional AstraZeneca ADSs or AstraZeneca ordinary shares deemed received) received by such U.S. Holder in exchange for its shares of Alexion common stock in the transaction, over (b) such U.S. Holder's tax basis in its shares of Alexion common stock exchanged. In addition, a U.S. Holder generally will recognize gain or loss with respect to any cash received in lieu of fractional AstraZeneca ADSs or AstraZeneca ordinary shares.

        A Non-U.S. Holder exchanging its shares of Alexion common stock for the merger consideration generally will not be subject to U.S. federal income tax in respect of the transaction.

        For definitions of "U.S. Holder" and "Non-U.S. Holder" and a more detailed discussion of the material U.S. federal income tax consequences of the transaction to U.S. Holders and Non-U.S. Holders, see the section entitled "Material U.S. Federal Income Tax Consequences" below.

        The U.S. federal income tax consequences described above may not apply to all holders of Alexion common stock. An Alexion stockholder's tax consequences will depend on his, her or its individual situation. Accordingly, each Alexion stockholder is urged to consult his, her or its tax advisors for a full understanding of the particular tax consequences of the transaction to such stockholder.

Accounting Treatment of the Transaction (page 86)

        The transaction will be accounted for as a business combination using the acquisition method of accounting in accordance with IFRS under IFRS 3, Business Combinations, which requires that one of the two companies in the transaction be designated as the acquirer for accounting purposes based on the evidence available. AstraZeneca will be treated as the accounting acquirer, and accordingly, will record assets acquired, including identifiable intangible assets, and liabilities assumed from Alexion at their respective fair values at the date of completion of the transaction. Any excess of the purchase price over the net fair value of such assets and liabilities will be recorded as goodwill. For a more detailed discussion of the accounting treatment of the transaction, see the section entitled "The Merger Proposal—Accounting Treatment of the Transaction."

Treatment of Alexion Equity Awards (page 111)

Alexion Stock Options

        At the first effective time, each outstanding Alexion Stock Option, whether vested or unvested, will automatically be cancelled in consideration for the right to receive, within five business days following the first effective time, the merger consideration, without interest and less applicable withholding taxes, in respect of each net option share subject to such Alexion Stock Option immediately prior to the first effective time, with the number of net option shares calculated as described in the merger agreement.

Alexion Restricted Stock Unit Awards

        At the first effective time, each Alexion RSU Award, will be treated as follows:

        If such Alexion RSU Award is held by a non-employee director of Alexion, it will automatically become fully vested and cancelled and converted into the right to receive, within five business days following the first effective time, the merger consideration, without interest and less applicable withholding taxes, with respect to each share of Alexion common stock subject to such Alexion RSU Award immediately prior to the first effective time.

        Each other Alexion RSU Award will be assumed by AstraZeneca and will be converted into an equivalent AstraZeneca restricted stock unit award, with the number of AstraZeneca ADSs underlying each converted award determined by multiplying the equity award exchange ratio as described in the merger agreement by the number of shares of Alexion common stock subject to such Alexion RSU Award.

Alexion Performance Stock Unit Awards

        At the first effective time, each Alexion PSU Award will be assumed by AstraZeneca and will be converted into an equivalent AstraZeneca restricted stock unit award, with the number of AstraZeneca ADSs underlying each converted award determined by multiplying the equity award exchange ratio as described in the merger agreement by the number of shares of Alexion common stock subject to such Alexion RSU Award (determined by deeming the applicable performance goals to be achieved at the greater of the target level and the actual level of achievement through the latest practicable date prior to the first effective time, subject to a limit of 175% of target for Alexion PSU Awards granted in 2019 and 150% of target for Alexion PSU Awards granted in 2020).

        For a description of the treatment of Alexion equity awards, see the section entitled "The Merger Agreement—Treatment of Alexion Equity Awards."

Regulatory Approvals Required for the Transaction (page 87)

        Completion of the transaction is conditioned upon the expiration or early termination of the waiting period relating to the transaction under the HSR Act and the receipt of approvals under the antitrust and foreign investment laws of certain specified foreign jurisdictions. Under the HSR Act, certain transactions, including the transaction, may not be completed unless certain waiting period requirements have expired or been terminated. The HSR Act provides that each party must file a pre-merger notification with the Federal Trade Commission, which is referred to in this proxy statement/prospectus as the "FTC," and the Antitrust Division of the U.S. Department of Justice, which is referred to in this proxy statement/prospectus as the "DOJ." A transaction notifiable under the HSR Act may not be completed until the expiration of a 30-calendar-day waiting period following the parties' filings of their respective HSR Act notification forms or the early termination of that waiting period. At any time before the expiration of the initial waiting period, the DOJ or the FTC may issue a Request for Additional Information and Documentary Material, which is referred to in this proxy statement/prospectus as a "Second Request." If a Second Request is issued, the parties may not complete the transaction until they each substantially comply with the Second Request and observe a second 30-calendar-day waiting period, unless the waiting period is terminated earlier.

        Each of AstraZeneca and Alexion filed its respective HSR Act notification and report with respect to the transaction on February 10, 2021. Following informal discussions with the FTC, AstraZeneca notified the FTC that it elected to withdraw and refile its notification and report form under the HSR Act prior to expiration of the initial waiting period to give the FTC additional time to review the proposed transaction. AstraZeneca's notification and report form was withdrawn effective as of March 12, 2021, and AstraZeneca refiled its notification on March 16, 2021, commencing a new

30-calendar-day waiting period under the HSR Act. In addition, the European Commission and certain other non-U.S. governmental authorities must approve, or be notified of, the transaction, and AstraZeneca and/or Alexion and/or their respective subsidiaries will file all such statements, notices or applications, as are necessary, proper or advisable according to the laws of relevant non-U.S. governmental authorities. AstraZeneca and Alexion have agreed to use their respective reasonable best efforts to take, or cause to be taken, all actions and to do, or cause to be done, all things necessary, proper or advisable to consummate the transaction, including (i) preparing and filing as promptly as practicable with any governmental authority or other third party all documentation to effect all filings necessary, proper or advisable to complete the transaction, (ii) using reasonable best efforts to obtain, as promptly as practicable, and thereafter maintain, all consents from any governmental authority or other third party that are necessary, proper or advisable to consummate the transaction and complying with the terms and conditions of each consent, and (iii) cooperating with the other parties, to the extent reasonable, in their efforts to comply with their obligations under the merger agreement. AstraZeneca and Alexion are also required to use their reasonable best efforts to defend any governmental action challenging the legality of the transaction and contest any order prohibiting the parties from completing the transaction.

        Additionally, AstraZeneca and its affiliates are required to take, or cause to be taken, all actions, and do or cause to be done, all things necessary, proper or advisable to eliminate each and every impediment under any antitrust law that is asserted by any governmental authority, obtain the consent or cooperation of any other person and permit and cause the satisfaction of the conditions to closing regarding the receipt of required regulatory approvals to permit the closing to occur as promptly as reasonably practicable and in any event prior to the end date, including: (i) proposing, negotiating, committing to, effecting and agreeing to, by consent decree, hold separate order, or otherwise, the sale, divestiture, license, holding separate, and other disposition of or restrictions on the businesses, assets, properties, product lines, and equity or other business interests of, or changes to the conduct of business of, Alexion, AstraZeneca, and their respective affiliates, and take all actions necessary or appropriate in furtherance of the foregoing, (ii) creating, terminating, unwinding, divesting or assigning, subcontracting or otherwise securing substitute parties for relationships, ventures, and contractual or commercial rights or obligations of Alexion, AstraZeneca, and their respective affiliates and (iii) otherwise taking or committing to take any action that would limit AstraZeneca's freedom of action with respect to, or its ability to retain, hold or continue, directly or indirectly, any businesses, assets, properties, product lines, and equity or other business interests, relationships, ventures or contractual rights and obligations of Alexion, AstraZeneca and their respective affiliates. However, AstraZeneca's obligations to take or cause to be taken any actions described in this paragraph is subject to the right of AstraZeneca, in its good faith reasonable discretion, to take reasonable periods of time in order to advocate and negotiate with governmental authorities with respect to such actions. In addition, none of Alexion, AstraZeneca or their respective affiliates is required to agree to take or enter into any such action described in clauses (i) through (iii) of this paragraph that is not conditioned upon or that becomes effective prior to, the closing. For more information, including the definition of the outside date, see the section entitled "The Merger Agreement—Efforts to Consummate the Transaction."

Appraisal or Dissenters' Rights (page 88)

        If the transaction is completed, Alexion stockholders who do not vote in favor of the adoption of the merger agreement and who otherwise comply with the applicable provisions of Section 262 of the DGCL will be entitled to exercise appraisal rights thereunder and obtain payment in cash for the fair value of their shares of Alexion, subject to certain limitations under the DGCL. Any shares of Alexion common stock held by an Alexion stockholder on the date of making an appraisal demand, who continues to own such shares through the first effective date, who has not voted in favor of the adoption of the merger agreement and who has demanded appraisal for such shares in accordance with

the DGCL will have the right to obtain payment in cash for the fair value of their shares of Alexion in lieu of the merger consideration, unless such Alexion stockholder fails to perfect, effectively withdraws, waives or otherwise loses such stockholder's appraisal rights under the DGCL. If, after the completion of the transaction, such holder of Alexion common stock fails to perfect, effectively withdraws, waives or otherwise loses his, her or its appraisal rights, each such share will be treated as if it had been converted as of the completion of the transaction into a right to receive the merger consideration. Due to the complexity of the procedures for exercising your appraisal rights, Alexion stockholders who are considering exercising such rights are encouraged to seek the advice of legal counsel. Failure to strictly comply with these provisions will result in the loss of appraisal rights. See the section titled "The Merger Proposal—Appraisal or Dissenters' Rights" contained in this proxy statement/prospectus for additional information and the text of Section 262 of the DGCL, which is included as Annex C to this proxy statement/prospectus, which you are encouraged to read carefully and in their entirety.

Litigation Relating to the Transaction (page 94)

        In connection with the transaction, nine complaints have been filed by purported Alexion stockholders against Alexion and its directors, and, in certain cases, AstraZeneca and the Merger Subs. The complaints are captioned Votto v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-02067 (S.D.N.Y); Wang v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-02095 (S.D.N.Y.); Wei v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-02100 (S.D.N.Y.); Naquin v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-02119 (S.D.N.Y.); Raul v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-02238 (S.D.N.Y.); Parshall v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-02670 (S.D.N.Y.); Davis v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-01429 (E.D.N.Y.); Kent v. Alexion Pharmaceuticals, Inc., et al., No. 1:21-cv-00441 (D. Del.); McKenzie v. Alexion Pharmaceuticals, Inc., et al., No. 2:21-cv-01515 (E.D. Pa.). The complaints generally allege that the preliminary registration statement filed with the SEC on February 19, 2021, omitted certain allegedly material information in connection with the transaction, and one of the complaints further alleges that the Alexion directors breached their fiduciary duties in connection with the transaction and that AstraZeneca and the other entity defendants aided and abetted the alleged breaches. The lawsuits seek various remedies, including enjoining the consummation of the transaction unless certain allegedly material information is disclosed, directing dissemination of additional allegedly material disclosures, rescission of the transaction, or rescissory damages in the event the transaction is consummated without such disclosures, and an accounting to the plaintiffs for any damages allegedly suffered. Given the early stage of the proceedings, it is impossible to predict the outcome or to estimate possible loss or range of loss.

Description of Debt Financing (page 94)

        AstraZeneca's obligation to complete the transaction is not contingent on the receipt by AstraZeneca of any financing. AstraZeneca estimates that it will need approximately $17.5 billion in order to pay Alexion stockholders the cash amounts due to them as merger consideration under the merger agreement and related fees and transaction costs in connection with the transaction, and fund the repayment of certain existing indebtedness of Alexion.

        AstraZeneca anticipates that the funds needed to pay the foregoing amount will be derived from a combination of some or all of (i) cash on hand, (ii) borrowings under its existing and new credit facilities described below and (iii) the proceeds from the sale of debt securities.

        In connection with entry into the merger agreement, on December 12, 2020, AstraZeneca and certain of its subsidiaries entered into a bridge facility agreement, the credit facility established in accordance with the terms thereof is referred to in this proxy statement/prospectus as the bridge facility, with Morgan Stanley Bank International Limited, J.P. Morgan Securities plc and Goldman Sachs Bank USA, respectively, to finance up to $17.5 billion of the (i) cash consideration in connection

with the transaction, (ii) repayment of certain existing indebtedness of Alexion or its subsidiaries and (iii) fees and expenses in connection with the foregoing. Morgan Stanley Senior Funding, Inc., Morgan Stanley Bank NA, JPMorgan Chase Bank, N.A., London Branch and Goldman Sachs Bank USA each provided a commitment to fund loans under the bridge facility and are collectively referred to in this proxy statement/prospectus as the initial bridge commitment parties.

        On December 24, 2020, the bridge facility was successfully syndicated to a number of large, well regarded international banks, and are collectively referred to, together with the initial bridge commitment parties, the bridge commitment parties, and $5 billion of the bridge facility was cancelled and refinanced with new long term credit facilities made available by the bridge commitment parties, which facilities are referred to in this proxy statement/prospectus as the take-out facilities, and the commitment parties in relation to the take-out facilities, the take-out commitment parties.

        The bridge commitment parties' obligation to fund the bridge facility and the take-out commitment parties' obligation to fund the take-out facilities are subject to certain limited conditions as set forth in the bridge facility agreement and the take-out facilities agreement, respectively, including, among others, all relevant consents to the transaction having been received, all conditions to closing under the merger agreement have been satisfied and that the transaction will be consummated substantially simultaneously with the first utilization of the relevant facility, and other customary conditions to completion. The commitments to provide the financing under the bridge facility are available for an initial term of 12 months from the earlier of (i) the date of completion of the acquisition and (ii) December 12, 2021, with up to two six-month extensions available at the discretion of AstraZeneca. The commitments to provide the term loan financing under the take-out facilities are available for a period which corresponds with the period in which closing can occur under the merger agreement.

        For more information, see the section entitled "The Merger Proposal—Description of Debt Financing."

Comparison of Shareholders' Rights (page 159)

        For a summary of the material differences between the rights of AstraZeneca shareholders and the existing rights of Alexion stockholders, see the section entitled "Comparison of AstraZeneca Shareholders and Alexion Stockholders Rights."

Conditions to the Transaction (page 113)

        Each party's obligation to complete the transaction is subject to the satisfaction or waiver of the following mutual conditions:

•

adoption of the merger agreement by Alexion stockholders;



•

approval of the transactions contemplated by the merger agreement by the AstraZeneca shareholders;



•

approval of the AstraZeneca ADSs (and the ordinary shares represented thereby) to be issued in the transaction for listing on Nasdaq, subject to official notice of issuance;



•

approval by the FCA of the application for admission of the ordinary shares represented by the AstraZeneca ADSs to be issued in connection with the transaction to the premium segment of the FCA's official list;



•

the LSE having acknowledged that the ordinary shares represented by the AstraZeneca ADSs to be issued in connection with the transaction shall be admitted to trading on the LSE's main market for listed securities;

•

expiration or early termination of the waiting period applicable to the completion of the transaction under the HSR Act and the receipt of required approvals under the antitrust laws and foreign investment laws of certain specified foreign jurisdictions;



•

effectiveness of the registration statement for the AstraZeneca ordinary shares to be issued in the transaction (of which this proxy statement/prospectus forms a part) and of the registration statement on Form F-6 relating to the AstraZeneca ADSs and the absence of any stop order suspending that effectiveness or any proceedings for that purpose pending before the SEC;



•

the absence of any injunction or order issued by any court or other governmental authority of competent jurisdiction that remains in effect and enjoins, prevents or prohibits completion of the transaction, and the absence of any applicable law enacted, entered or promulgated by any governmental authority that remains in effect and prohibits or makes illegal completion of the transaction; and



•

approval by the FCA of the shareholder circular and the distribution thereof to AstraZeneca shareholders in accordance with the FCA's listing rules and the memorandum and articles of association of AstraZeneca.

        The obligations of AstraZeneca, Bidco and each Merger Sub to complete the transaction are subject to the satisfaction or waiver of further conditions, including:

•

the accuracy of the representations and warranties of Alexion contained in the merger agreement as of the date of the merger agreement and as of the closing date (other than representations that by their terms speak specifically as of another date), subject to the materiality standards provided in the merger agreement;



•

Alexion having performed in all material respects the obligations required to be performed by it under the merger agreement at or prior to the first effective time; and



•

AstraZeneca's receipt of a certificate of an executive officer of Alexion, certifying that the conditions set forth in the two bullets directly above have been satisfied.

        The obligation of Alexion to complete the transaction is subject to the satisfaction or waiver of further conditions, including:

•

the accuracy of the representations and warranties of AstraZeneca, Bidco and each Merger Sub contained in the merger agreement as of the date of the merger agreement and as of the closing date (other than representations that by their terms speak specifically as of another date), subject to the materiality standards provided in the merger agreement;



•

each of AstraZeneca, Bidco and each Merger Sub having performed in all material respects the obligations required to be performed by it under the merger agreement at or prior to the first effective time;



•

Alexion's receipt of a certificate of an executive officer of AstraZeneca, certifying that the conditions set forth in the two bullets directly above have been satisfied; and



•

the receipt by Alexion of an opinion from Wachtell, Lipton, Rosen & Katz, special counsel to Alexion, or Freshfields Bruckhaus Deringer US LLP, counsel to AstraZeneca, dated as of the closing date, in form and substance reasonably satisfactory to Alexion, to the effect that, on the basis of facts, representations and assumptions set forth or referred to in such opinion, the transaction will qualify as a "reorganization" within the meaning of Section 368(a) of the Code and that Section 367(a)(1) of the Code will not apply to cause the transaction to result in gain recognition to Alexion stockholders (other than any such Alexion stockholder who would be treated as a "five-percent transferee shareholder" (within the meaning of Treasury Regulations Section 1.367(a)-3(c)(5)(ii)) of AstraZeneca following the transaction who does not enter into a

five-year gain recognition agreement in the form provided in Treasury Regulations Section 1.367(a)-8).

No Solicitation (page 123)

        The merger agreement generally restricts Alexion's and AstraZeneca's ability to: (i) solicit, initiate, knowingly facilitate or knowingly encourage (including by way of furnishing information) any inquiries regarding, or the making or submission of any acquisition proposal, (ii) (A) enter into or participate in any discussions or negotiations regarding, (B) furnish to any third party any information or (C) otherwise assist, participate in, knowingly facilitate or knowingly encourage any third party, in each case, in connection with or for the purpose of knowingly encouraging or facilitating, an acquisition proposal, or (iii) approve, recommend or enter into or publicly or formally propose to approve, recommend or enter into, any letter of intent or similar document, agreement, commitment or agreement in principle (whether written or oral, binding or nonbinding) with respect to an acquisition proposal.

        However, under certain circumstances specified in the merger agreement, Alexion or AstraZeneca, as applicable, is permitted to furnish information with respect to it and its subsidiaries to third parties and participate in discussions or negotiations with such third parties in response to unsolicited acquisition proposals if, prior to taking such action, such party's board of directors determines in good faith, after consultation with outside legal counsel and financial advisor, that based on the information then available and after consultation with its outside legal counsel and financial advisor, such acquisition proposal either constitutes a "superior proposal" (as defined in the section entitled "The Merger Agreement—No Solicitation") or could reasonably be expected to result in a superior proposal.

        For further information, including what constitutes an "acquisition proposal" and a "superior proposal," see the section entitled "The Merger Agreement—No Solicitation."

Termination of the Merger Agreement (page 133)

        Subject to conditions and circumstances described in the merger agreement, the merger agreement may be terminated as follows:

•

by mutual written consent of Alexion and AstraZeneca;



•

by either Alexion or AstraZeneca if the transaction is not completed by December 12, 2021, subject to extension until March 12, 2022, in specified circumstances;



•

by either Alexion or AstraZeneca if: (i) AstraZeneca shareholders fail to approve the transactions contemplated by the merger agreement upon a vote taken on a proposal to approve the transactions contemplated by the merger agreement at the AstraZeneca shareholder meeting or (ii) Alexion stockholders fail to adopt the merger agreement upon a vote taken on a proposal to adopt the merger agreement at the Alexion special meeting;



•

by either Alexion or AstraZeneca if a governmental entity issues a final and non-appealable injunction permanently restraining or enjoining the completion of the transaction;



•

by AstraZeneca if: (i) Alexion breaches any of its representations or warranties or fails to perform any of the covenants or agreements under the merger agreement, and such breach or failure to perform (a) would give rise to the failure of a closing condition and (b) is incapable of being cured prior to the end date or is not cured within the earlier of 45 days after the giving of notice thereof by AstraZeneca or the end date, or (ii) prior to the adoption of the merger agreement by Alexion stockholders, (a) the Alexion Board makes an adverse recommendation change, (b) Alexion fails to publicly confirm to Alexion stockholders, within 10 business days after the commencement of a tender or exchange offer subject to Regulation 14D under the

U.S. Exchange Act that constitutes an acquisition proposal, that Alexion recommends rejection of such tender or exchange offer (or shall have withdrawn any such rejection thereafter), or (c) Alexion commits a wilful breach of its no solicit obligations or its obligation to hold the Alexion special meeting; and

•

by Alexion if: (i) AstraZeneca, Bidco or either Merger Sub breaches any of its representations or warranties or fails to perform any of the covenants or agreements under the merger agreement, and such breach or failure to perform (a) would give rise to the failure of a closing condition and (b) is incapable of being cured prior to the end date or is not cured within the earlier of 45 days after the giving of notice thereof by Alexion or the end date, (ii) prior to the approval of the transactions contemplated by the merger agreement by Alexion stockholders, (a) the AstraZeneca Board makes an adverse recommendation change, (b) AstraZeneca fails to publicly confirm to AstraZeneca shareholders, within ten business days after the commencement of an offer (as defined in the U.K. Code) or tender or exchange offer subject to Regulation 14D under the U.S. Exchange Act that constitutes an acquisition proposal, that AstraZeneca recommends rejection of such offer or tender or exchange offer (or shall have withdrawn any such rejection thereafter), or (c) AstraZeneca commits a wilful breach of its no solicit obligations or its obligation to hold the AstraZeneca special meeting or (iii) prior to the adoption of the merger agreement by Alexion stockholders, Alexion terminates the merger agreement in order to enter into a definitive agreement providing for a superior proposal.

Your Rights as an AstraZeneca Shareholder Will Be Different from Your Rights as an Alexion Stockholder (page 159)

        Upon the completion of the transaction, each eligible share of Alexion common stock will be converted into the right to receive the merger consideration, consisting of (1) 2.1243 AstraZeneca ADSs (or, at the election of the holder thereof, a number of ordinary shares of AstraZeneca equal to the number of underlying ordinary shares represented by such AstraZeneca ADSs) and (2) $60.00 in cash, without interest. As a result, Alexion stockholders will have different rights once they become AstraZeneca shareholders (whether directly or via their holding of AstraZeneca ADSs) due to differences between the organizational documents of AstraZeneca and Alexion and differences between Delaware law, where Alexion is incorporated, and the laws of England and Wales, where AstraZeneca is incorporated. For a summary of the material differences between the rights of AstraZeneca shareholders and the existing rights of Alexion stockholders, see the section entitled "Comparison of Rights of AstraZeneca Shareholders and Alexion Stockholders."

Interests of Alexion's Directors and Executive Officers in the Transaction (page 79)

        In considering the recommendation of the Alexion board of directors to adopt the merger agreement, Alexion stockholders should be aware that Alexion's directors and executive officers have interests in the transaction that may be different from, or in addition to, the interests of Alexion stockholders generally, including potential severance benefits, treatment of outstanding Alexion equity awards in connection with the transaction, potential transaction bonuses, and rights to ongoing indemnification and insurance coverage. Alexion's board of directors was aware of these interests and considered them, among other matters, in evaluating and negotiating the merger agreement, in reaching its decision to approve and declare advisable the merger agreement and the transactions contemplated by the merger agreement (including the transaction), and in recommending to Alexion stockholders that the merger agreement be approved.

        These interests are discussed in more detail in the section entitled "The Merger Proposal—Interests of Alexion's Directors and Executive Officers in the Transaction." The Alexion board of directors was aware of the different or additional interests described herein and considered these interests along with other matters in approving and adopting the merger agreement.

Recent Developments (page 104)

        On December 17, 2015, AstraZeneca entered into an agreement to acquire 55% of the entire issued share capital of Acerta Pharma ("Acerta") for an upfront payment of US$2.5 billion, which was paid in 2016. A further payment of US$1.5 billion was paid in 2017 on receipt of the first regulatory approval for Calquence (acalabrutinib) for any indication in the U.S. The agreement included options which, if exercised, provided the opportunity for Acerta shareholders to sell, and AstraZeneca to buy, the remaining 45% of shares in Acerta. The final condition for these options to be exercised was satisfied in November 2020 when Calquence (acalabrutinib) received marketing approval in the EU. AstraZeneca exercised its option to acquire the remaining 45% of shares in Acerta in April 2021.

        The agreement originally provided that the remaining 45% of shares in Acerta would be acquired at a price of approximately US$3 billion net of certain costs and payments incurred by AstraZeneca and net of agreed future adjusting items, using a pre-agreed pricing mechanism. In October 2019, an amendment agreement came into effect, changing the timing of payments and reducing the maximum consideration that would be required to be made to acquire the remaining outstanding shares of Acerta if the options were exercised. The payments are to be made in similar annual installments in 2022, 2023 and 2024. The changes to the terms were reflected in the assumptions which were used to calculate the amortized cost of the option liability as at December 31, 2020 of US$2.3 billion.