AMVUTTRA® (vutrisiran) Significantly Reduces Mortality and a Range of Important Cardiovascular Events in Patients with ATTR Amyloidosis with Cardiomyopathy: Additional Data from HELIOS-B

– Analysis Presented at the Heart Failure 2025 Congress Supports Primary Findings, Highlighting Impact of AMVUTTRA, which Delivers Rapid Knockdown of Transthyretin –

– Additional 42-Month Data Reinforce Vutrisiran's Impact on the Risk of All-Cause Mortality and Further Underscore the Effect on Cardiovascular Mortality –

– Vutrisiran Demonstrated Substantial Benefit Across a Range of Cardiovascular Events, Notably Reducing Urgent Heart Failure Visits by 46% in the Overall Patient Population During the Double-Blind Period –

– Findings Simultaneously Published in JACC –

– Details of TRITON-CM Phase 3 Study Evaluating Alnylam's Investigational Next-Generation TTR Silencer, Nucresiran, to be Presented at Congress –

Alnylam Pharmaceuticals, Inc. (NASDAQ:ALNY), the leading RNAi therapeutics company, today presented the most contemporary analysis of the HELIOS-B Phase 3 study of vutrisiran for the treatment of ATTR amyloidosis with cardiomyopathy (ATTR-CM) as a late-breaking abstract at the Heart Failure 2025 Congress, a scientific congress of the European Society of Cardiology, taking place May 17-20 in Belgrade, Serbia. The results demonstrate that vutrisiran, which rapidly knocks down transthyretin, reduces key cardiovascular (CV) events such as CV hospitalizations, and heart failure (HF) hospitalizations. Additionally, in the analysis, urgent HF visits were reduced by 46% (95% CI: 0.30, 0.98; p = 0.041) in the overall population during the double-blind period, compared to placebo. These CV events often precede all-cause mortality (ACM) and are key indicators of disease progression.

Importantly, results from the November 2024 data cut, including further follow up through up to 42 months, reinforce the primary HELIOS-B analysis showing vutrisiran's effect on ACM, and further demonstrate that vutrisiran reduces CV mortality. Through 42 months, the risk of ACM was reduced by 36% (95% CI: 0.46, 0.88; p = 0.007) and the risk of CV mortality was reduced by 33% (95% CI: 0.47, 0.96; p = 0.038) in the overall population, compared to placebo. For both the primary analysis and the current analysis, vital status through 42 months was ascertained for over 99% of all randomized patients from the HELIOS-B study, underscoring the robustness of the results.

The study was conducted in a contemporary patient population with patients receiving robust background therapy, inclusive of treatment with a TTR stabilizer and SGLT2 inhibitors. The analysis of the HELIOS-B Phase 3 study, including mortality data through up to 42 months, was simultaneously published in JACC.

"From the primary analysis of HELIOS-B, we know that AMVUTTRA profoundly impacts all-cause mortality, while preserving patients' functional capacity and quality of life," said Pushkal Garg, M.D., Chief Medical Officer of Alnylam. "These new data—including the impact on mortality, on cardiovascular events and on urgent heart failure visits, the latter of which was reduced by nearly half—add to the story of consistency and magnitude of benefit. I remain impressed by the HELIOS-B results, which are noteworthy given the substantial use of heart failure treatments in the study population, and I believe they continue to reinforce AMVUTTRA as a clinically differentiated, first-line option for patients with ATTR-CM."

The results from the analysis underscore the rapid and sustained benefits of vutrisiran in treating ATTR-CM across key endpoints:

In a separate presentation on Tuesday, May 20, Alnylam will share findings from a subgroup analysis of HELIOS-B evaluating the impact of vutrisiran on ACM and recurrent CV events among patients identified by investigators as having experienced disease progression while being treated with tafamidis.

Also at the Heart Failure 2025 Congress, Alnylam will present the study design and rationale for TRITON-CM, a Phase 3, randomized, double-blind, study of nucresiran in patients with ATTR-CM. Nucresiran is an investigational next-generation RNAi therapeutic targeting TTR that has been shown to deliver rapid knockdown of TTR greater than 95% with twice-annual dosing in a Phase 1 study. TRITON-CM is an event-driven CV outcomes trial with a primary endpoint of composite ACM and CV events. The study is on track to initiate in the first half of 2025 and will enroll approximately 1,200 patients with wild-type or variant TTR and confirmed cardiomyopathy, including those receiving background stabilizer therapy. Additional details of the study's secondary endpoints and key inclusion and exclusion criteria will be shared on Monday, May 19.

AMVUTTRA^® (vutrisiran) was approved by the U.S. Food and Drug Administration (FDA) and the Brazilian Health Regulatory Agency (ANVISA) for treatment of the cardiomyopathy of wild-type or hereditary transthyretin-mediated amyloidosis in adults. The Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) has adopted a positive opinion recommending the approval of vutrisiran for the same indication. A formal regulatory decision by the European Commission of the EMA is expected by the third quarter of 2025. Vutrisiran is currently under review for the treatment of ATTR-CM by the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). Alnylam remains on track to proceed with additional global regulatory submissions for vutrisiran in 2025 and beyond.

For additional information on Alnylam's presentations at the Heart Failure 2025 Congress, please visit Capella.

Indications and Important Safety Information

Indications Approved by the U.S. FDA

AMVUTTRA^® (vutrisiran) is indicated for the treatment of the:

• cardiomyopathy of wild-type or hereditary transthyretin-mediated amyloidosis (ATTR-CM) in adults to reduce cardiovascular mortality, cardiovascular hospitalizations and urgent heart failure visits.
• polyneuropathy of hereditary transthyretin-mediated amyloidosis (hATTR-PN) in adults.

Important Safety Information

Reduced Serum Vitamin A Levels and Recommended Supplementation

AMVUTTRA treatment leads to a decrease in serum vitamin A levels.

Supplementation at the recommended daily allowance (RDA) of vitamin A is advised for patients taking AMVUTTRA. Higher doses than the RDA should not be given to try to achieve normal serum vitamin A levels during treatment with AMVUTTRA, as serum vitamin A levels do not reflect the total vitamin A in the body.

Patients should be referred to an ophthalmologist if they develop ocular symptoms suggestive of vitamin A deficiency (e.g., night blindness).

Adverse Reactions

In a study of patients with hATTR-PN, the most common adverse reactions that occurred in patients treated with AMVUTTRA were pain in extremity (15%), arthralgia (11%), dyspnea (7%), and vitamin A decreased (7%).

In a study of patients with ATTR-CM, no new safety issues were identified.

For additional information about AMVUTTRA, please see the full U.S. Prescribing Information (revised March 2025)

About AMVUTTRA^® (vutrisiran)

AMVUTTRA^® (vutrisiran) is an RNAi therapeutic that delivers rapid knockdown of variant and wild-type transthyretin (TTR), addressing the underlying cause of transthyretin (ATTR) amyloidosis. Administered quarterly via subcutaneous injection, vutrisiran is approved and marketed in more than 15 countries for the treatment of the polyneuropathy of hereditary transthyretin-mediated amyloidosis (hATTR-PN) in adults. In Europe, it is administered as a subcutaneous injection once every three months, either by a healthcare professional, or self-administered by patients or their caregivers. Vutrisiran is also in development for the treatment of ATTR amyloidosis with cardiomyopathy (ATTR-CM), which encompasses both wild-type and hereditary forms of the disease.

About ATTR

Transthyretin amyloidosis (ATTR) is an underdiagnosed, rapidly progressive, debilitating and fatal disease caused by misfolded transthyretin (TTR) proteins, which accumulate as amyloid deposits in various parts of the body, including the nerves, heart and gastrointestinal tract. Patients may present with polyneuropathy, cardiomyopathy, or both manifestations of disease. There are two different forms of ATTR – hereditary ATTR (hATTR), which is caused by a TTR gene variant and affects approximately 50,000 people worldwide, and wild-type ATTR (wtATTR), which occurs without a TTR gene variant and impacts an estimated 200,000 – 300,000 people worldwide.^1-4

About RNAi

RNAi (RNA interference) is a natural cellular process of gene silencing that represents one of the most promising and rapidly advancing frontiers in biology and drug development today. Its discovery has been heralded as "a major scientific breakthrough that happens once every decade or so," and was recognized with the award of the 2006 Nobel Prize for Physiology or Medicine. By harnessing the natural biological process of RNAi occurring in our cells, a new class of medicines known as RNAi therapeutics is now a reality. Small interfering RNA (siRNA), the molecules that mediate RNAi and comprise Alnylam's RNAi therapeutic platform, function upstream of today's medicines by potently silencing messenger RNA (mRNA) – the genetic precursors – that encode for disease-causing or disease pathway proteins, thus preventing them from being made. This is a revolutionary approach with the potential to transform the care of patients with genetic and other diseases.

About Alnylam Pharmaceuticals

Alnylam (NASDAQ:ALNY) has led the translation of RNA interference (RNAi) into a whole new class of innovative medicines with the potential to transform the lives of people afflicted with rare and prevalent diseases with unmet need. Based on Nobel Prize-winning science, RNAi therapeutics represent a powerful, clinically validated approach yielding transformative medicines. Since its founding in 2002, Alnylam has led the RNAi Revolution and continues to deliver on a bold vision to turn scientific possibility into reality. Alnylam has a deep pipeline of investigational medicines, including multiple product candidates that are in late-stage development. Alnylam is executing on its "Alnylam P⁵x25" strategy to deliver transformative medicines in both rare and common diseases benefiting patients around the world through sustainable innovation and exceptional financial performance, resulting in a leading biotech profile. Alnylam is headquartered in Cambridge, MA.

Alnylam Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. All statements other than historical statements of fact regarding Alnylam's expectations, beliefs, goals, plans or prospects including, without limitation, Alnylam's expectations regarding the safety and efficacy of vutrisiran for the treatment of ATTR-CM, including the ability of vutrisiran to reduce mortality and cardiovascular events in ATTR-CM patients and to preserve patients' functional capacity and quality of life; the potential for vutrisiran to become a first-line therapy for ATTR-CM; the timing of the initiation of the TRITON-CM study and the number of patients who will be enrolled in that study; the timing of additional global regulatory submissions for vutrisiran; the timing or receipt of any additional regulatory approvals for vutrisiran for ATTR-CM; Alnylam's ability to execute on its "Alnylam P⁵x25" strategy and to deliver transformative medicines in both rare and common diseases benefit patients around the world through sustainable innovation and exceptional financial performance; and Alnylam's ability to have a leading biotech profile should be considered forward-looking statements.

Actual results and future plans may differ materially from those indicated by these forward-looking statements as a result of various important risks, uncertainties and other factors, including, without limitation, risks and uncertainties relating to Alnylam's ability to successfully execute on its "Alnylam P⁵x25" strategy; Alnylam's ability to discover and develop novel drug candidates and delivery approaches and successfully demonstrate the efficacy and safety of its product candidates; the pre-clinical and clinical results for Alnylam's product candidates; actions or advice of regulatory agencies and Alnylam's ability to obtain and maintain regulatory approval for its product candidates, as well as favorable pricing and reimbursement; successfully launching, marketing and selling Alnylam's approved products globally; delays, interruptions or failures in the manufacture and supply of Alnylam's product candidates or its marketed products; obtaining, maintaining and protecting intellectual property; Alnylam's ability to manage its growth and operating expenses through disciplined investment in operations and its ability to achieve a self-sustainable financial profile in the future; Alnylam's ability to maintain strategic business collaborations; Alnylam's dependence on third parties for the development and commercialization of certain products; the outcome of litigation; the potential risk of future government investigations; and unexpected expenditures; as well as those risks more fully discussed in the "Risk Factors" filed with Alnylam's 2024 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC), as may be updated from time to time in Alnylam's subsequent Quarterly Reports on Form 10-Q, and in other filings that Alnylam makes with the SEC. In addition, any forward-looking statements represent Alnylam's views only as of today and should not be relied upon as representing Alnylam's views as of any subsequent date. Alnylam explicitly disclaims any obligation, except to the extent required by law, to update any forward-looking statements.

¹ Hawkins PN, Ando Y, Dispenzeri A, et al. Ann Med. 2015;47(8):625-638.

² Gertz MA. Am J Manag Care. 2017;23(7):S107-S112.

³ Conceicao I, Gonzalez-Duarte A, Obici L, et al. J Peripher Nerv Syst. 2016;21:5-9.

⁴ Ando Y, Coelho T, Berk JL, et al. Orphanet J Rare Dis. 2013;8:31.

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