SNY Sanofi

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of March 2025

Commission File Number: 001-31368

SANOFI

(Translation of registrant’s name into English)

46, avenue de la Grande Armée, 75017 Paris, FRANCE

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.

Form 20-F ☒   Form 40-F ☐

1

In March 2025, Sanofi published the press releases attached hereto as Exhibits 99.1 and 99.2 which are incorporated herein by reference.

Exhibit Index

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

3

Exhibit 99.1

Press Release

Tolebrutinib regulatory submission accepted for priority review in the US for patients with multiple sclerosis

Paris, March 25, 2025. The US Food and Drug Administration (FDA) is evaluating under priority review the regulatory submission of tolebrutinib to treat non-relapsing secondary progressive multiple sclerosis (nrSPMS) and to slow disability accumulation independent of relapse activity in adult patients. The target action date for the FDA decision is September 28, 2025. A regulatory submission is also under review in the EU.

The regulatory submissions in the US and the EU are supported by the results from the phase 3 studies HERCULES in nrSPMS and GEMINI 1 and 2 in relapsing MS (RMS). The findings from these studies, as well as additional clinical and preclinical studies, support the differentiated mechanism of tolebrutinib to target disability progression independent of relapse activity, and the scientific hypothesis that smoldering neuroinflammation represents a key inflammatory process in MS and is a critical driver of disability accumulation.

Erik Wallström, MD, PhD

Global Head of Neurology Development

“The totality of data across our clinical program validates our scientific understanding of smoldering neuroinflammation as a distinct inflammatory process in MS. People living with non-relapsing secondary progressive multiple sclerosis or who experience disability independent of relapse activity suffer from disability that worsens over time due to persistent inflammation in the brain, known as smoldering neuroinflammation, which is the primary driver of disability. The demonstrated ability of tolebrutinib to delay disability by targeting underlying drivers of the disease represents a potential paradigm shift in treating these patients.”

Tolebrutinib is currently under clinical investigation, and its safety and efficacy have not been evaluated by any regulatory authority. The PERSEUS phase 3 study of tolebrutinib in patients with primary progressive MS is currently ongoing with study results anticipated in H2 2025.

About multiple sclerosis

Multiple sclerosis is a chronic, immune-mediated, neurodegenerative disease that may result in accumulation of irreversible disabilities over time. The physical and cognitive disability impairments translate into gradual deterioration of health status, impacting patients’ care and quality of life. Disability accumulation remains the significant unmet medical need in MS. To date, the primary target of currently approved medicines has been peripheral B and T cells, while innate immunity within the CNS, which is believed to drive disability accumulation, remains largely unaddressed. Currently approved or late-stage medicines being tested for MS mainly target the adaptive immune system and/or do not act directly within the central nervous system to drive clinical benefit.

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Living with nrSPMS refers to people with MS who have stopped experiencing relapses but continue to accumulate disability, experienced as symptoms such as fatigue, cognitive impairment, balance and gait impairment, loss of bowel and/or bladder function, sexual disfunction, amongst others.

About tolebrutinib

Tolebrutinib is an investigational, oral, brain-penetrant, and bioactive Bruton’s tyrosine kinase (BTK) inhibitor specifically designed to target smoldering neuroinflammation, a key driver of disability progression in MS. Unlike currently approved MS therapies that primarily address peripheral inflammation, tolebrutinib uniquely crosses the blood-brain barrier to achieve therapeutic cerebrospinal fluid concentrations, allowing it to modulate B-lymphocytes and disease-associated microglia within the CNS. This mechanism is believed to address the underlying pathology of progressive MS by targeting the inflammatory processes that contribute to neurodegeneration and disability accumulation.

Tolebrutinib is being evaluated in phase 3 clinical studies for the treatment of various forms of multiple sclerosis and its safety and efficacy have not been evaluated by any regulatory authority worldwide. For more information on tolebrutinib clinical studies, please visit www.clinicaltrials.gov.

About HERCULES

HERCULES (clinical study identifier: NCT04411641) was a double-blind randomized phase 3 clinical study evaluating the efficacy and safety of tolebrutinib in patients with nrSPMS. At baseline, nrSPMS was defined as having a SPMS diagnosis with an expanded disability status scale (EDSS) between 3.0 and 6.5, no clinical relapses for the previous 24 months and documented evidence of disability accumulation in the previous 12 months. Participants were randomized (2:1) to receive either an oral daily dose of tolebrutinib or matching placebo for up to approximately 48 months.

The primary endpoint was 6-month CDP defined as the increase of ≥1.0 point from the baseline EDSS score when the baseline score is ≤5.0, or the increase of ≥0.5 point when the baseline EDSS score was >5.0. Secondary endpoints included time to onset of 3-month CDP as assessed by EDSS score, total number of new or enlarging T2 hyperintense lesions as detected by MRI, time to onset of confirmed disability improvement, 3-month change in 9-hole peg test and T25-FW test as well as the safety and tolerability of tolebrutinib.

About GEMINI 1 and 2

GEMINI 1 (clinical study identifier: NCT04410978) and GEMINI 2 (clinical study identifier: NCT04410991) were double-blind randomized phase 3 clinical studies evaluating the efficacy and safety of tolebrutinib compared to teriflunomide in patients with RMS. Participants were randomized in both studies (1:1) to receive either tolebrutinib and placebo daily or 14mg teriflunomide and placebo.

The primary endpoint for both studies was the annualized relapse rate for up to approximately 36 months defined as the number of confirmed adjudicated protocol defined relapses. Secondary endpoints included time to onset of CDW, confirmed over at least 6 months, defined as an increase of ≥1.5 points from the baseline EDSS score when the baseline score is 0, an increase of ≥1.0 point from the baseline EDSS score when the baseline score is 0.5 to ≤5.5 or an increase of ≥0.5 point from the baseline EDSS score when the baseline score was >5.5 in addition to the total number of new and/or enlarging T2 hyperintense lesions as detected by MRI from baseline through the end of study, the total number of Gd-enhancing T1 hyperintense lesions as detected by MRI from baseline through the end of study and the safety and tolerability of tolebrutinib.

About Sanofi

We are an innovative global healthcare company, driven by one purpose: we chase the miracles of science to improve people’s lives. Our team, across the world, is dedicated to transforming the practice of medicine by working to turn the impossible into the possible. We provide potentially life-changing treatment options and life-saving vaccine protection to

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millions of people globally, while putting sustainability and social responsibility at the center of our ambitions.

Sanofi is listed on EURONEXT: SAN and NASDAQ: SNY

Media Relations

Sandrine Guendoul | +33 6 25 09 14 25 | sandrine.guendoul@sanofi.com

Evan Berland | +1 215 432 0234 | evan.berland@sanofi.com

Nicolas Obrist | +33 6 77 21 27 55 | nicolas.obrist@sanofi.com

Léo Le Bourhis | +33 6 75 06 43 81 | leo.lebourhis@sanofi.com

Victor Rouault | +33 6 70 93 71 40 | victor.rouault@sanofi.com

Timothy Gilbert | +1 516 521 2929 | timothy.gilbert@sanofi.com

Investor Relations

Thomas Kudsk Larsen |+44 7545 513 693 | thomas.larsen@sanofi.com

Alizé Kaisserian | +33 6 47 04 12 11 | alize.kaisserian@sanofi.com

Felix Lauscher | +1 908 612 7239 | felix.lauscher@sanofi.com

Keita Browne | +1 781 249 1766 | keita.browne@sanofi.com

Nathalie Pham | +33 7 85 93 30 17 | nathalie.pham@sanofi.com

Tarik Elgoutni | +1 617 710 3587 | tarik.elgoutni@sanofi.com

Thibaud Châtelet | +33 6 80 80 89 90 | thibaud.chatelet@sanofi.com

Yun Li | +33 6 84 00 90 72 |yun.li3@sanofi.com

Sanofi forward-looking statement

This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements are statements that are not historical facts. These statements include projections and estimates and their underlying assumptions, statements regarding plans, objectives, intentions, and expectations with respect to future financial results, events, operations, services, product development and potential, and statements regarding future performance. Forward-looking statements are generally identified by the words “expects”, “anticipates”, “believes”, “intends”, “estimates”, “plans” and similar expressions. Although Sanofi’s management believes that the expectations reflected in such forward-looking statements are reasonable, investors are cautioned that forward-looking information and statements are subject to various risks and uncertainties, many of which are difficult to predict and generally beyond the control of Sanofi, that could cause actual results and developments to differ materially from those expressed in, or implied or projected by, the forward-looking information and statements. These risks and uncertainties include among other things, the uncertainties inherent in research and development, future clinical data and analysis, including post marketing, decisions by regulatory authorities, such as the FDA or the EMA, regarding whether and when to approve any drug, device or biological application that may be filed for any such product candidates as well as their decisions regarding labelling and other matters that could affect the availability or commercial potential of such product candidates, the fact that product candidates if approved may not be commercially successful, the future approval and commercial success of therapeutic alternatives, Sanofi’s ability to benefit from external growth opportunities, to complete related transactions and/or obtain regulatory clearances, risks associated with intellectual property and any related pending or future litigation and the ultimate outcome of such litigation, trends in exchange rates and prevailing interest rates, volatile economic and market conditions, cost containment initiatives and subsequent changes thereto, and the impact that global crises may have on us, our customers, suppliers, vendors, and other business partners, and the financial condition of any one of them, as well as on our employees and on the global economy as a whole. The risks and uncertainties also include the uncertainties discussed or identified in the public filings with the SEC and the AMF made by Sanofi, including those listed under “Risk Factors” and “Cautionary Statement Regarding Forward-Looking Statements” in Sanofi’s annual report on Form 20-F for the year ended December 31, 2024. Other than as required by applicable law, Sanofi does not undertake any obligation to update or revise any forward-looking information or statements.

All trademarks mentioned in this press release are the property of the Sanofi group.

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Exhibit 99.2

Press Release

Chlamydia vaccine candidate granted fast track designation by the US FDA

Paris, March 26, 2025. The US Food and Drug Administration has granted fast track designation to Sanofi’s mRNA vaccine candidate for the prevention of chlamydia infection. The decision was based on the potential of the vaccine candidate to address a serious condition and address an unmet public health need.

The chlamydia vaccine candidate has been designed to protect against primary genital tract infection and reinfection by the bacterium Chlamydia trachomatis. Following a promising pre-clinical program, Sanofi is planning a phase 1/2 randomized, clinical study designed to evaluate the immunogenicity and safety of the chlamydia vaccine candidate in adults aged 18 to 29 years. The study is due to start in coming days.

Jean-François Toussaint

Global Head of Vaccines R&D

“Millions of people currently live with undiagnosed chlamydia, including asymptomatic infection that can also cause severe long-term health effects if left untreated. Antibiotics to treat chlamydia have not been successful in controlling rising infection rates. With our program we aim to make chlamydia a preventable disease through vaccination.”

Chlamydia, caused by the bacterium Chlamydia trachomatis, is a common bacterial infection of the reproductive tract with consequences for developing infertility and pregnancy complications. In 2020, there were 129 million worldwide cases of chlamydia among adults (15-49 years old), with the highest rates of infection among adolescents and young adults.

Although chlamydia can be treated with antibiotics when diagnosed, over 80% of chlamydia cases are asymptomatic, meaning there is a significant risk that infections go unrecognized, leading to untreated cases and unintentional transmission. Programs that have been put in place to prevent infection rates from rising have proven insufficient, highlighting the urgent public health need for a vaccine.

The development of this vaccine candidate is part of the Translational Science Hub, a partnership with the Queensland Government, Griffith University, and the University of Queensland, connecting world-class researchers in Queensland, Australia, with Sanofi scientists in France and the US.

About Sanofi

We are an innovative global healthcare company, driven by one purpose: we chase the miracles of science to improve people’s lives. Our team, across the world, is dedicated to transforming the practice of medicine by working to turn the impossible into the possible. We provide potentially life-changing treatment options and life-saving vaccine protection to millions of people globally, while putting sustainability and social responsibility at the center of our ambitions.

Sanofi is listed on EURONEXT: SAN and NASDAQ: SNY

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Media Relations

Sandrine Guendoul | + 33 6 25 09 14 25 | sandrine.guendoul@sanofi.com

Evan Berland | +1 215 432 0234 | evan.berland@sanofi.com

Nicolas Obrist | + 33 6 77 21 27 55 | nicolas.obrist@sanofi.com

Léo Le Bourhis | + 33 6 75 06 43 81 | leo.lebourhis@sanofi.com

Victor Rouault | + 33 6 70 93 71 40 | victor.rouault@sanofi.com

Timothy Gilbert | + 1 516 521 2929 | timothy.gilbert@sanofi.com

Investor Relations

Thomas Kudsk Larsen |+ 44 7545 513 693 | thomas.larsen@sanofi.com

Alizé Kaisserian | + 33 6 47 04 12 11 | alize.kaisserian@sanofi.com

Felix Lauscher | + 1 908 612 7239 | felix.lauscher@sanofi.com

Keita Browne | + 1 781 249 1766 | keita.browne@sanofi.com

Nathalie Pham | + 33 7 85 93 30 17 | nathalie.pham@sanofi.com

Tarik Elgoutni | + 1 617 710 3587 | tarik.elgoutni@sanofi.com

Thibaud Châtelet | + 33 6 80 80 89 90 | thibaud.chatelet@sanofi.com

Yun Li |+ 33 6 84 00 90 72 | yun.li3@sanofi.com

Sanofi forward-looking statements

This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements are statements that are not historical facts. These statements include projections and estimates and their underlying assumptions, statements regarding plans, objectives, intentions, and expectations with respect to future financial results, events, operations, services, product development and potential, and statements regarding future performance. Forward-looking statements are generally identified by the words “expects”, “anticipates”, “believes”, “intends”, “estimates”, “plans” and similar expressions. Although Sanofi’s management believes that the expectations reflected in such forward-looking statements are reasonable, investors are cautioned that forward-looking information and statements are subject to various risks and uncertainties, many of which are difficult to predict and generally beyond the control of Sanofi, that could cause actual results and developments to differ materially from those expressed in, or implied or projected by, the forward-looking information and statements. These risks and uncertainties include among other things, the uncertainties inherent in research and development, future clinical data and analysis, including post marketing, decisions by regulatory authorities, such as the FDA or the EMA, regarding whether and when to approve any drug, device or biological application that may be filed for any such product candidates as well as their decisions regarding labelling and other matters that could affect the availability or commercial potential of such product candidates, the fact that product candidates if approved may not be commercially successful, the future approval and commercial success of therapeutic alternatives, Sanofi’s ability to benefit from external growth opportunities, to complete related transactions and/or obtain regulatory clearances, risks associated with intellectual property and any related pending or future litigation and the ultimate outcome of such litigation, trends in exchange rates and prevailing interest rates, volatile economic and market conditions, cost containment initiatives and subsequent changes thereto, and the impact that global crises may have on us, our customers, suppliers, vendors, and other business partners, and the financial condition of any one of them, as well as on our employees and on the global economy as a whole. The risks and uncertainties also include the uncertainties discussed or identified in the public filings with the SEC and the AMF made by Sanofi, including those listed under “Risk Factors” and “Cautionary Statement Regarding Forward-Looking Statements” in Sanofi’s annual report on Form 20-F for the year ended December 31, 2024. Other than as required by applicable law, Sanofi does not undertake any obligation to update or revise any forward-looking information or statements.

All trademarks mentioned in this press release are the property of the Sanofi group.

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