Employee Letter (Form SC14D9C)

Employee Letter

To: All Cidara Employees

From: Jeff Stein, President & Chief Executive Officer

Subject: Merck to Acquire Cidara Therapeutics in $9.2 Billion All-Cash Transaction

All,

I am excited to share transformational news for Cidara. This morning, we announced that we have entered into a definitive agreement to be acquired by Merck, through a subsidiary, for $221.50 per share. A press release announcing this news was issued just moments ago - you can access the link here: Merck to Acquire Cidara Therapeutics, Inc., Diversifying Its Portfolio to Include Late-Phase Antiviral Agent.

This is an incredible milestone for all of us and a testament to how far we have come together. I am confident that this transaction represents the best possible path forward for our science, our people, and our investors. Importantly, your collective efforts in the creation and development of CD388 have enabled the long-sought goal of a universal preventative of influenza.

This all-cash transaction values Cidara at approximately $9.2 billion, which represents a premium of 109% to yesterday's closing share price and 794% to our share price at the beginning of the year. This reflects the broad recognition of the enormous value you have helped create. I feel privileged and humbled to have had the opportunity to work alongside all of you to advance CD388 and Cidara to where we are today.

As you are likely aware, Merck is a research-driven global biopharmaceutical company with an extensive portfolio across medicines, vaccines, biologic therapies, and animal health products. By combining our groundbreaking science with Merck's global development, regulatory, and commercial capabilities, we will be far better positioned to unlock the full potential of CD388 as a universal, non-vaccine, long-acting option for flu prevention for millions of people globally.

Until the transaction closes, which we expect in the first quarter of 2026, Cidara and Merck will continue to operate as separate companies, and our priorities remain unchanged. We are marching full steam ahead on our Phase 3 ANCHOR study, which is now almost fully enrolled, and it is essential that we maintain our focus and momentum.

This announcement represents day one in the process for Cidara to join Merck. We know you will have questions, and while we do not yet have every answer, we are committed to open and transparent communication as we progress toward the closing of the transaction. As a first step, we will host an all-hands meeting today at 10:00 AM PT / 1:00 PM ET to discuss what this announcement means for the Company and you. Please make every effort to join.

Finally, we do expect this news to generate increased interest in Cidara from external parties. As a reminder, all communications with analysts, investors, stockholders, media, and other members of the public about the Company are to be made by designated spokespeople only. Per our policy, if you receive any inquiries, please do not respond and instead forward the inquiry to Frank Karbe or me.

I want to reiterate that this announcement is a validation of your talent and the contributions of each of you. I couldn't be prouder of the company we have built, the clinical progress we have made, and the lifesaving influenza preventative we are working to bring to patients. I hope you join us in celebrating today's achievement.

Thank you,

Jeff

Additional Information about the Tender Offer Transactions and Where to Find It

The tender offer described in this communication has not yet commenced. This communication is for information purposes only and is neither an offer to buy nor a solicitation of an offer to sell any securities of Cidara. The solicitation and the offer to buy securities of Cidara will only be made pursuant to tender offer materials that Merck and its wholly owned acquisition subsidiary Caymus Purchaser, Inc. will file with the Securities and Exchange Commission (the "SEC"). The solicitation of the offer to buy shares of Cidara's Common Stock and shares of Cidara's Series A Preferred Stock will only be made pursuant to a tender offer statement on Schedule TO, including an offer to purchase, a letter of transmittal and other related material that Merck intends to file with the SEC. Cidara will also file with the SEC a Solicitation/Recommendation Statement on Schedule 14D-9 with respect to the tender offer. Once filed, investors will be able to obtain the tender offer statement on Schedule TO, the offer to purchase and the Solicitation/Recommendation Statement of Cidara on Schedule 14D-9 and related materials with respect to the tender offer and the merger free of charge at the website of the SEC at www.sec.gov or from the information agent named in the tender offer materials. Investors may also obtain, at no charge, the documents filed with or furnished to the SEC by Cidara under the "Investors" section of Cidara's website at www.cidara.com.

Investors are strongly advised to read these documents when they become available, including the Solicitation/Recommendation Statement of Cidara on Schedule 14D-9 and any amendments thereto, as well as any other documents relating to the tender offer and the merger that are filed with the SEC, carefully and in their entirety prior to making any decisions with respect to whether to tender their shares into the tender offer because they contain important information, including the terms and conditions of the tender offer.