Exhibit 99.1

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Kiniksa Pharmaceuticals Reports Second Quarter 2026 Financial Results and Recent Portfolio Execution

– ARCALYST^® (rilonacept) Q2 2026 net product revenue of $243.6 million, representing ~55% year-over-year growth –

– ARCALYST 2026 expected net product revenue increased to $980 - $995 million –

– KPL-387 Phase 2 data demonstrated rapid and sustained reductions in pain and inflammation at 300 mg SC once-monthly, the dose level selected for Phase 3 –

– KPL-387 pivotal Phase 3 trial in recurrent pericarditis now enrolling and dosing patients –

– Conference call and webcast scheduled for 8:30 am ET today –

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London – July 28, 2026 – Kiniksa Pharmaceuticals International, plc (Nasdaq: KNSA) (Kiniksa), a biopharmaceutical company developing and commercializing novel therapies for diseases with unmet need, with a focus on cardiovascular indications, today reported second quarter 2026 financial results and recent portfolio execution.

“In the second quarter, Kiniksa continued to drive growth in new and repeat prescribers of ARCALYST in recurrent pericarditis, which led to a meaningful increase in patients on therapy. As a result, we have raised our 2026 ARCALYST net sales guidance to between $980 and $995 million,” said Sanj K. Patel, Chairman & Chief Executive Officer of Kiniksa. “In our clinical portfolio, KPL-387 Phase 2 data supported initiation of the pivotal Phase 3 trial, PASTORALE, which is now enrolling and dosing patients. We are excited to advance KPL-387 with its target product profile of once-monthly subcutaneous dosing in a liquid formulation. We expect to bring this potential additional treatment option to patients in the 2028/2029 timeframe. Additionally, we continue to develop KPL-1161 with a target profile of once-quarterly dosing and are on track to initiate a Phase 1 trial by the end of this year.”

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Portfolio Execution

ARCALYST (IL-1α and IL-1β cytokine trap)

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KPL-387 (monoclonal antibody IL-1 receptor antagonist)

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KPL-1161 (Fc-modified monoclonal antibody IL-1 receptor antagonist)

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^* Reported as median (95% confidence interval).

¹ Treatment Response is defined as Pain Response (NRS score ≤ 2 on the 11-point daily pericarditis pain NRS pain scale) and at least one CRP level ≤ 0.5 mg/dL within 7 days before or after the Pain Response.

² CRP Normalization is defined as CRP ≤ 0.5 mg/dL.

Financial Results

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Financial Guidance

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Conference Call Information

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About Kiniksa

Kiniksa is a biopharmaceutical company dedicated to improving the lives of patients suffering from debilitating diseases by discovering, acquiring, developing, and commercializing novel therapies for diseases with unmet need, with a focus on cardiovascular indications. Kiniksa’s portfolio of assets is based on strong biologic rationale or validated mechanisms and offers the potential for differentiation. For more information, please visit www.kiniksa.com.

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About ARCALYST

ARCALYST is a weekly, subcutaneously injected recombinant dimeric fusion protein that blocks interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) signaling. ARCALYST was discovered by Regeneron Pharmaceuticals, Inc. (Regeneron) and is approved by the U.S. Food and Drug Administration (FDA) for recurrent pericarditis, cryopyrin-associated periodic syndromes (CAPS), including Familial Cold Autoinflammatory Syndrome and Muckle-Wells Syndrome, and deficiency of IL-1 receptor antagonist (DIRA). The FDA granted Breakthrough Therapy designation to ARCALYST for the treatment of recurrent pericarditis in 2019 and Orphan Drug exclusivity to ARCALYST in 2021 for the treatment of recurrent pericarditis and reduction in risk of recurrence in adults and pediatric patients 12 years and older. The European Commission granted Orphan Drug Designation to ARCALYST for the treatment of idiopathic pericarditis in 2021.

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IMPORTANT SAFETY INFORMATION ABOUT ARCALYST

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For more information about ARCALYST, talk to your doctor and see the Product Information.

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About KPL-387

KPL-387 is an independently developed, investigational, fully human immunoglobulin G2 (IgG2) monoclonal antibody that binds human interleukin-1 receptor 1 (IL-1R1), inhibiting the signaling of the cytokines IL-1α and IL-1β. Kiniksa believes KPL-387 could expand the treatment options for recurrent pericarditis patients by potentially enabling dosing with a single monthly SC self-injection in a liquid formulation. In October 2025, the FDA granted Orphan Drug Designation to KPL-387 for the treatment of pericarditis.

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About PASTORALE

PASTORALE is a double-blind, placebo controlled, randomized withdrawal (RW) study enrolling up to approximately 85 patients with recurrent pericarditis. In the first period, a single-blind run-in (RI), all participants will receive KPL-387 while conventional oral pericarditis medications are weaned and discontinued. Participants achieving Clinical Response in the RI period will then be randomized in a 1:1 ratio to receive either KPL-387 300 mg SC once-monthly or placebo in an event-driven, double-blind, RW period. The primary efficacy endpoint is time to first-adjudicated pericarditis recurrence during the RW period. Participants in the RW period may be eligible to enter a long-term extension.

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About KPL-1161

KPL-1161 is an independently developed, investigational, Fc-modified IgG2 monoclonal antibody that binds IL-1R1, inhibiting the signaling of the cytokines IL-1α and IL-1β, with a target profile of quarterly SC dosing. Kiniksa is currently engaging in preclinical development activities for KPL-1161.

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Forward-Looking Statements

This press release contains forward-looking statements. In some cases, you can identify forward looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions, although not all forward-looking statements contain these identifying words. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation, statements regarding: our expectation that ARCALYST 2026 net product revenue will be between $980 million and $995 million; our expectation to begin commercialization of KPL-387 in 2028 or 2029; our belief that we are on track to initiate a Phase 1 first-in-human clinical trial of KPL-1161 by the end of 2026; our expectation that our current operating plan will remain cash flow positive on an annual basis; our target profile of quarterly subcutaneous dosing for KPL-1161; our beliefs about the mechanisms of our assets and potential impact of their approach; statements regarding our belief about the future of our commercial opportunities; and our belief that our portfolio of assets offers the potential for differentiation.

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These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially

different from any future results, performance or achievements expressed or implied by the forward-looking statements, including without limitation, the following: delays or difficulty in enrollment of patients in, and activation or continuation of sites for, our clinical trials; delays or difficulty in completing our clinical trials as originally designed; potential for changes between final data and any preliminary, interim, top-line or other data from clinical trials, including the data from the interval analysis of our Phase 2 clinical trial of KPL-387 in recurrent pericarditis; our inability to replicate results from our earlier clinical trials or studies; impact of additional data from us or other companies, including the potential for our data to produce negative, inconclusive or commercially uncompetitive results; our reliance on third parties to conduct research, clinical trials, and/or certain regulatory activities for our product candidates; complications in coordinating requirements, regulations and guidelines of regulatory authorities across jurisdictions for our clinical trials; potential undesirable side effects caused by our products and product candidates; our inability to demonstrate safety and efficacy to the satisfaction of applicable regulatory authorities; potential for applicable regulatory authorities to not accept our filings, delay or deny approval of any of our product candidates or require additional data or trials to support approval; our reliance on third parties as the sole source of supply of the drug substance and drug product used in our products and product candidates; raw material, important ancillary product and drug substance and/or drug product shortages; business development activities and their impact on our financial performance and strategy; changes in our operating plan, business development strategy or funding requirements; existing or new competition; current and future healthcare reforms, including those affecting the delivery of or payment for healthcare products and services; and the impact of global economic policy, including any uncertainty in national and international markets.

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These and other important factors discussed in our filings with the U.S. Securities and Exchange Commission, including under the caption “Risk Factors” contained therein, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. Except as required by law, we disclaim any intention or obligation to update or revise any forward-looking statements. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release.

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ARCALYST^® is a registered trademark of Regeneron Pharmaceuticals, Inc.

Every Second Counts! ^®

Kiniksa Investor & Media Contact

Jonathan Kirshenbaum

(781) 829-3949

jkirshenbaum@kiniksa.com

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