Filed by Shire plc

pursuant to Rule 425 under the Securities Act

of 1933 and deemed filed pursuant to

Rule 14a-12 of the Securities Exchange

Act of 1934

Subject Company: Baxalta Incorporated

Commission File No. 001-36782

Forward-Looking Statements

Statements included herein that are not historical facts, including without limitation statements concerning our proposed business combination with Baxalta Incorporated (“Baxalta”) and the timing and financial and strategic benefits thereof, our 20x20 ambition that targets $20 billion in combined product sales by 2020, as well as other targets for future financial results, capital structure, performance and sustainability of the combined company, the combined company’s future strategy, plans, objectives, expectations and intentions, the anticipated timing of clinical trials and approvals for, and the commercial potential of, inline or pipeline products are forward-looking statements. Such forward-looking statements involve a number of risks and uncertainties and are subject to change at any time. In the event such risks or uncertainties materialize, Shire’s results could be materially adversely affected. The risks and uncertainties include, but are not limited to, the following:

·the proposed combination with Baxalta may not be completed due to a failure to satisfy certain closing conditions, including any shareholder or regulatory approvals or the receipt of applicable tax opinions;

·the businesses may not be integrated successfully, such integration may be more difficult, time-consuming or costly than expected, or the expected benefits of the transaction may not be realized;

·disruption from the proposed transaction may make it more difficult to conduct business as usual or maintain relationships with patients, physicians, employees or suppliers;

·the combined company may not achieve some or all of the anticipated benefits of Baxalta’s spin-off from Baxter International, Inc. (“Baxter”) and the proposed transaction may have an adverse impact on Baxalta’s existing arrangements with Baxter, including those related to transition, manufacturing and supply services and tax matters;

·the failure to achieve the strategic objectives with respect to the proposed combination with Baxalta may adversely affect the combined company’s financial condition and results of operations;

·Shire may not complete its proposed acquisition of Dyax Corp. (“Dyax”) due to the occurrence of an event, change or other circumstances that gives rise to the termination of the relevant merger agreement or the failure to satisfy certain closing conditions, including the Dyax shareholder approval;

·products and product candidates may not achieve commercial success;

·product sales from ADDERALL XR and INTUNIV are subject to generic competition;

·the failure to obtain and maintain reimbursement, or an adequate level of reimbursement, by third-party payers in a timely manner for the combined company’s products may affect future

revenues, financial condition and results of operations, particularly if there is pressure on pricing of products to treat rare diseases;

·supply chain or manufacturing disruptions may result in declines in revenue for affected products and commercial traction from competitors; regulatory actions associated with product approvals or changes to manufacturing sites, ingredients or manufacturing processes could lead to significant delays, an increase in operating costs, lost product sales, an interruption of research activities or the delay of new product launches;

·the successful development of products in various stages of research and development is highly uncertain and requires significant expenditures and time, and there is no guarantee that these products will receive regulatory approval;

·the actions of certain customers could affect the combined company’s ability to sell or market products profitably, and fluctuations in buying or distribution patterns by such customers can adversely affect the combined company’s revenues, financial condition or results of operations;

·investigations or enforcement action by regulatory authorities or law enforcement agencies relating to the combined company’s activities in the highly regulated markets in which it operates may result in significant legal costs and the payment of substantial compensation or fines;

·adverse outcomes in legal matters and other disputes, including the combined company’s ability to enforce and defend patents and other intellectual property rights required for its business, could have a material adverse effect on the combined company’s revenues, financial condition or results of operations;

·Shire is undergoing a corporate reorganization and was the subject of an unsuccessful acquisition proposal and the consequent uncertainty could adversely affect the combined company’s ability to attract and/or retain the highly skilled personnel needed to meet its strategic objectives;

·failure to achieve the strategic objectives with respect to Shire’s acquisition of NPS Pharmaceuticals Inc. or Dyax may adversely affect the combined company’s financial condition and results of operations;

·the combined company will be dependent on information technology and its systems and infrastructure face certain risks, including from service disruptions, the loss of sensitive or confidential information, cyber-attacks and other security breaches or data leakages that could have a material adverse effect on the combined company’s revenues, financial condition or results of operations;

·the combined company may be unable to retain and hire key personnel and/or maintain its relationships with customers, suppliers and other business partners;

·difficulties in integrating Dyax or Baxalta into Shire may lead to the combined company not being able to realize the expected operating efficiencies, cost savings, revenue enhancements, synergies or other benefits at the time anticipated or at all; and

other risks and uncertainties detailed from time to time in Shire’s, Dyax’s or Baxalta’s filings with the Securities and Exchange Commission (“SEC”), including those risks outlined in Baxalta’s current Registration Statement on Form S-1, as amended, and in “Item 1A: Risk Factors” in Shire’s Annual Report on Form 10-K for the year ended December 31, 2014.

All forward-looking statements attributable to us or any person acting on our behalf are expressly qualified in their entirety by this cautionary statement. Readers are cautioned not to place undue reliance on these forward-looking statements that speak only as of the date hereof. Except to the extent otherwise required by applicable law, we do not undertake any obligation to republish revised forward-looking statements to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

Additional Information

This communication does not constitute an offer to buy or solicitation of any offer to sell securities or a solicitation of any vote or approval. It does not constitute a prospectus or prospectus equivalent document. This communication relates to the proposed business combination between Shire and Baxalta. The proposed combination will be submitted to Shire’s and Baxalta’s shareholders for their consideration and approval. In connection with the proposed combination, Shire and Baxalta will file relevant materials with (i) the SEC, including a Shire registration statement on Form S-4 that will include a proxy statement of Baxalta and a prospectus of Shire, and (ii) the Financial Conduct Authority (FCA) in the UK, including a prospectus relating to Shire ordinary shares to be issued in connection with the proposed combination and a circular to the shareholders of Shire. Baxalta will mail the proxy statement/prospectus to its shareholders and Shire will mail the circular to its shareholders. This communication is not a substitute for the registration statement, proxy statement/prospectus, UK prospectus, circular or other document(s) that Shire and/or Baxalta may file with the SEC or the FCA in connection with the proposed transaction. INVESTORS AND SECURITY HOLDERS OF SHIRE AND BAXALTA ARE URGED TO READ CAREFULLY THE REGISTRATION STATEMENT,PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS FILED WITH THE SEC AND THE UK PROSPECTUS AND CIRCULAR WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT SHIRE, BAXALTA AND THE PROPOSED TRANSACTION. Investors and security holders may obtain free copies of these documents (when they are available) and other related documents filed with the SEC at the SEC’s web site at www.sec.gov. Investors may request copies of the documents filed with the SEC by Shire by directing a request to Shire’s Investor Relations department at Shire plc, Attention: Investor Relations, 300 Shire Way, Lexington, MA 02421 or to Shire’s Investor Relations department at +1 484 595 2220 in the U.S. and +44 1256 894157 in the UK or by email to investorrelations@shire.com.  Investors may request copies of the documents filed with the SEC by Baxalta by directing a request to Mary Kay Ladone at mary.kayklandone@baxalta.com or (224) 948-3371.

The statements in this presentation are Shire’s statements and not those of Baxalta or any third party.

Certain Information Regarding Participants

Shire, Baxalta and their respective directors and executive officers may be deemed participants in the solicitation of proxies in connection with the proposed transaction. You can find information about Shire’s directors and executive officers in Shire’s Annual Report on Form 10-K for the year ended December 31, 2014, which was filed with the SEC on February 24, 2015.

You can find information about Baxalta’s directors and executive officers in Baxalta’s registration statement on Form S-1, which was filed with the SEC on September 1, 2015.Additional information regarding the special interests of these directors and executive officers in the proposed transaction will be included in the registration statement, proxy statement/prospectus or other documents filed with the SEC if any when they become available. You may obtain these documents (when they become available) free of charge at the SEC’s web site at www.sec.gov and from Investor Relations at Shire or Baxalta as described above.

This communication shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended.

Trademarks

Shire owns or has rights to use the trademarks, service marks and trade names that it uses in conjunction with the operation of its business. Some of the trademarks that Shire owns or has the rights to use that are referenced in this communication include: ADDERALL XR, CINRYZE, ELAPRASE, FIRAZYR, GATTEX/REVESTIVE, INTUNIV, LIALDA, NATPARA, REPLAGAL, PENTASA, VPRIV, VYVANSE and XAGRID.  Baxalta states that it owns or has the right to use certain trademarks referenced in this communication, including: ADVATE, ADYNOVATE, ARALAST, FEIBA, FLEXBUMIN, GAMMAGARD, GAMMAGARD LIQUID, GLASSIA, HYQVIA, OBIZUR, ONCASPAR, ONIVYDE, RECOMBINATE, RIXUBIS and SUBCUVIA, which may be registered or used in the United States and other jurisdictions.

Basis of Forecasts

The Shire forecasts included herein are derived from Shire’s Long Range Plan (the “LRP”) and Shire papers subsequently produced as part of the business planning process.  Shire produces a long range plan annually. The LRP was updated in March 2015, as part of Shire’s annual planning cycle, and was reviewed by the Board in April 2015.  This LRP was subsequently adjusted to reflect revised expectations for SHP625 following trial results in the second quarter of 2015, the Dyax acquisition and other updates for 2015 actual performance.

The forecast product sales in this announcement are consistent with the LRP, which is at constant exchange rates, and reflects net sales for each product and key line extensions currently identified as in Phase III, Phase II and those in Phase I included in the LRP as launching before the end of 2020.

The forecast product sales included in the LRP are risk-adjusted to reflect Shire’s assessment of the individual probability of launch of products in development, and the probability of success in further life cycle management trials.  Estimates for these probabilities are based on industry

wide data for relevant clinical trials in the pharmaceutical industry at a similar stage of development.

For each pharmaceutical product, there is a range of possible outcomes from clinical development, driven by a number of variables, including safety, efficacy and product labelling.  In addition, if a product is approved, the effect of commercial factors including the patient population, the competitive environment, pricing and reimbursement is also uncertain.  As a result, the actual net sales achieved by a product over its commercial life will be different, perhaps materially so, from the risk adjusted net sales figures in this announcement and should be considered in this light.

The forecast product sales for Baxalta included in this communication have been stated on a constant currency and risk adjusted basis.

Transcript of Flemming Ornskov Video Announcing the Merger of Shire plc and Baxalta Incorporated on Shire plc’s Website

Hello - I am Flemming Ornskov, the Chief Executive Officer of Shire.

As many of you may know, we have announced that Shire entered into an agreement to combine with Baxalta, creating the global leader in rare diseases.

I want to take this opportunity to tell you why I am so excited about the proposed combination.

[pause]

This transaction will combine two strategically aligned companies, which are expected to deliver $20 billion in revenues by 2020.

Our combined robust portfolio includes over 30 recent and planned product launches with an estimated $5B in sales potential by 2020, all of which address significant unmet patient needs.

At close, we will be the #1 platform in rare diseases.

Together, we will offer category leadership with best-in-class products in each of the following growing, multi-billion-dollar franchises:

[pause]

Hematology; Immunology; Neuroscience; Lysosomal Storage Diseases; Gastrointestinal / Endocrine; and Hereditary Angioedema.

The combined company will also have innovative compounds in development and approved products in Ophthalmics and Oncology, respectively.

The combined company will have expanded geographic reach and scale.

We will also have a diversified talent and a patient-driven, entrepreneurial culture focused on addressing unmet medical needs — all of which will drive further growth for our business.

[pause]

This deal is also expected to deliver double digit top line growth, operating cost synergies of over $500 million; accretion to non-GAAP earnings in 2017 and beyond; and an attractive ROIC.

Following the close of the transaction we look forward as a combined company to build on the drivers that have propelled both Shire and Baxalta —

...a laser focus on growth and innovation that is only possible through the enduring hard work and dedication of our collective employees.

It is their ongoing commitment to patients that allow us to succeed.

I thank you for your interest in Shire and I look forward to continuing to deliver results that will benefit our stakeholders around the globe.

Transcript of Flemming Ornskov Video Announcing the Merger of Shire plc and Baxalta Incorporated to Shire plc Employees

Good morning, good afternoon, or good evening —

I’m delighted to be speaking to you on one of the most exciting days in Shire’s history.

As many of you have likely heard, today we entered into an agreement to combine with Baxalta, creating a new global leader in rare diseases.

I want to take a few minutes to share with you directly my perspective on this big news.

The combination of Baxalta and Shire will create the number one rare diseases platform in revenue and pipeline depth, with best-in-class products in each of the following growing, multi-billion-dollar franchises:

[pause]

Hematology; Immunology; Neuroscience; Lysosomal Storage Diseases; Gastrointestinal / Endocrine; and Hereditary Angioedema.

The combined company will also have innovative compounds in development and approved products in Ophthalmics and Oncology, respectively.

We are also expanding our already-impressive rare diseases pipeline:

together, we will have more than 60 programs in development, of which over 50 address rare diseases.

We expect over 30 launches from this rare disease pipeline by 2020.

This is the largest pipeline of rare disease programs in the industry.

I fully expect the combined company to offer expanded opportunities for our employees around the globe.

With increased scale and infrastructure, and the most robust rare disease portfolio in the industry, this transaction will accelerate our growth and drive enhanced discovery and commercialization.

We will collaborate with new colleagues from Baxalta, foster even greater innovation and career development, including the ability to work in new therapeutic areas and geographies.

You will also have the opportunity to explore new directions and expand your careers — working with some of the industry’s best and brightest talents — in a truly entrepreneurial, patient-focused environment.

The integration process will begin immediately post-close, but for most in both companies it will be business as usual, and we will operate as separate companies until close.

As we progress through the integration milestones, we are committed to provide you with updates and answer your questions at the earliest possible opportunities along the way.

Thank you for all you do every day on behalf of the patients who count on us.

Today marks an unprecedented milestone in our transformation to a leading global biotech focused on rare diseases and specialty conditions.

We are in this position to join forces because of your efforts, and your ongoing commitment to the people we serve.

I’m counting on each of you for your continued support and commitment.

I look forward to taking this next step together, and to our bright future as the leading global biotech focused on rare diseases.

Shire plc Tweets (@Shireplc), January 11, 2016:

Shire plc @Shireplc  · Jan 11

Message from the CEO: Why #ShireBaxalta combination will drive sustained category leadership in #rarediseases http://rarediseaseleader.com/  $SHPG

[Link to https://twitter.com/Shireplc/status/686638709651992576]

Shire plc @Shireplc  · Jan 11

Follow #ShireBaxalta via our dedicated combination website: http://www.rarediseaseleader.com . $SHPG

[Link to https://twitter.com/Shireplc/status/686561370951782400]

Shire plc @Shireplc  · Jan 11

Shire will host a conference call for investors and analysts today at 8:30am EST. Dial in details are here: http://bit.ly/1nd8vHR

[Link to https://twitter.com/Shireplc/status/686533310793826304]

Shire plc @Shireplc  · Jan 11

#ShireBaxalta to combine, creating the global leader in #RareDiseases.

[Link to https://twitter.com/Shireplc/status/686526953927634944]

Shire plc LinkedIn [Link to https://www.linkedin.com/company/shire], January 11, 2016:

Shire: Follow #ShireBaxalta via our dedicated combination website: www.rarediseaseleader.com. Visit the site to learn more!

Shire:  Shire will host a conference call for investors and analysts today, January 11th, at 8:30am EST to discuss the combination of Shire and Baxalta. Please find dial-in details here: http://bit.ly/1nd8vHR

Shire:  The strategic combination of Shire and Baxalta will create the global leader in rare diseases. Learn more. #ShireBaxalta http://bit.ly/1OK9s4J

####