Ciena Set to Join S&P 500; Arrowhead Pharmaceuticals to Join S&P MidCap 400; ADT and OneSpaWorld Holdings to Join S&P SmallCap 600

Rhea-AI Summary

ADT (NYSE: ADT) will join the S&P SmallCap 600 effective prior to the opening of trading on Feb 9, 2026, as part of index changes by S&P Dow Jones Indices. The rebalancing also adds Ciena (CIEN) to the S&P 500 and moves Arrowhead Pharmaceuticals (ARWR) into the S&P MidCap 400 on Feb 9; OneSpaWorld (OSW) joins the SmallCap 600 on Feb 10.

Dayforce was removed following an acquisition by Thoma Bravo, and Dynavax was deleted ahead of its pending acquisition by Sanofi.

Positive

• Ciena added to S&P 500 on Feb 9, 2026
• ADT added to S&P SmallCap 600 on Feb 9, 2026
• OneSpaWorld added to S&P SmallCap 600 on Feb 10, 2026
• Arrowhead moved into S&P MidCap 400 on Feb 9, 2026

Negative

• Dayforce removed from S&P 500 after Thoma Bravo acquisition
• Arrowhead removed from S&P SmallCap 600 on Feb 9, 2026
• Dynavax removed from S&P SmallCap 600 ahead of pending Sanofi deal

News Market Reaction – DVAX

-0.13%

-0.13% Session close to close

In the Feb 5 session, DVAX declined 0.13%, reflecting a mild negative market reaction.

Data tracked by StockTitan Argus on the day of publication.

Market Context

This announcement details index rebalancing that removes Dynavax from the S&P SmallCap 600 as its ac...

Analysis

This announcement details index rebalancing that removes Dynavax from the S&P SmallCap 600 as its acquisition by Sanofi progresses. The company previously agreed to be acquired for $15.50 per share in cash, and recent SEC filings show insiders and a major shareholder tendering shares at that price. Investors monitoring this situation may focus on deal completion status, remaining regulatory steps, and how index removal affects trading dynamics around the agreed cash consideration.

Key Figures

Tender offer price: $15.50 per share Shares tendered: 15,726,349 shares Ownership post-deal: 0 shares (0%) +5 more

8 metrics

Tender offer price $15.50 per share Cash consideration in Sanofi acquisition and insider tender transactions

Shares tendered 15,726,349 shares Deep Track Biotechnology Master Fund tendered common shares at $15.50

Ownership post-deal 0 shares (0%) Deep Track Capital beneficial ownership after Sanofi merger

Shares outstanding 117,424,968 shares Referenced from Dynavax’s 10-Q filed Nov 5, 2025

Insider shares cashed out 60,204 shares CFO Kelly MacDonald common stock exchanged for $15.50 cash offer

VP share tender 7,129 shares Joseph Metzinger’s common shares tendered for $15.50 per share

RSUs cancelled 10,075 RSUs Director Emilio Emini’s restricted stock units cashed out at $15.50

Options exercised for cash 42,750 and 7,125 options Director Emini’s option grants vested then cancelled for cash at $15.50 less strike

Historical Context

5 past events · Latest: Dec 24 (Positive)

Pattern 5 events

Date	Event	Sentiment	24h Move	Catalyst
Dec 24	Acquisition by Sanofi	Positive	+38.2%	Sanofi agreed to acquire Dynavax for $15.50 per share, valuing equity at ~$2.2B.
Nov 19	Conference participation	Neutral	-2.3%	Announcement of participation in the 8th Annual Evercore Healthcare Conference with webcast access.
Nov 05	Earnings & buyback	Positive	+6.7%	Q3 2025 results, strong HEPLISAV-B growth, and launch of a $100M share repurchase program.
Nov 05	Licensing deal	Positive	+6.7%	Exclusive worldwide license for Vaxart’s oral COVID-19 vaccine with upfront, equity, and milestone structure.
Oct 22	Earnings call notice	Neutral	+0.4%	Scheduling of Q3 2025 earnings release and conference call with webcast and replay details.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Pattern Detected

Recent major corporate events, especially the Sanofi acquisition and positive financial/strategic updates, have generally seen the stock move in the same direction as the apparent sentiment of the news.

Recent Company History

Over the last several months, DVAX has been shaped by its acquisition by Sanofi and continued commercial progress. On Dec 24, 2025, Sanofi agreed to acquire Dynavax for $15.50 per share in cash (~$2.2B equity value), and the stock rose 38.19%. Earlier, Q3 2025 results plus a $100M buyback and strong HEPLISAV‑B metrics coincided with a 6.7% gain. Licensing of Vaxart’s oral COVID‑19 vaccine program on Nov 5, 2025 also aligned with that move. Routine conference and earnings-call announcements saw modest reactions, suggesting large strategic actions have driven the most material repricing.

Key Terms

S&P 500, S&P MidCap 400, S&P SmallCap 600

3 terms

S&P 500 financial

"Ciena Corp. (NYSE: CIEN) will replace Dayforce Inc. (NYSE: DAY) in the S&P 500"

The S&P 500 is a broad stock market index that tracks the performance of 500 large U.S. companies, weighted so bigger firms have a larger impact. Investors use it like a thermometer or benchmark to judge how the overall U.S. stock market or a portfolio is doing; movements in the index influence investor sentiment, fund performance, and many passive investment products that aim to match its returns.

View in glossary

S&P MidCap 400 financial

"Arrowhead Pharmaceuticals Inc. (NASD: ARWR) will replace Ciena in the S&P MidCap 400"

The S&P MidCap 400 is a group of 400 companies that are smaller than the big, well-known corporations but larger than tiny startups. It helps investors see how medium-sized companies are performing in the stock market, acting like a barometer for this middle-sized group of businesses.

S&P SmallCap 600 financial

"ADT Inc. (NYSE: ADT) will replace Arrowhead Pharmaceuticals in the S&P SmallCap 600"

A stock market index made up of 600 small-cap U.S. companies chosen to represent the performance of smaller publicly traded firms. It matters to investors because it acts like a temperature gauge for the small-company segment of the market, serving as a benchmark for fund managers, a basis for index funds and ETFs, and a way to compare returns and risk when building a diversified portfolio.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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NEW YORK, Feb. 4, 2026 /PRNewswire/ -- S&P Dow Jones Indices will make the following changes to the S&P 500, S&P MidCap 400, S&P SmallCap 600: 

• S&P MidCap 400 constituent Ciena Corp. (NYSE: CIEN) will replace Dayforce Inc. (NYSE: DAY) in the S&P 500, S&P SmallCap 600 constituent Arrowhead Pharmaceuticals Inc. (NASD: ARWR) will replace Ciena in the S&P MidCap 400, and ADT Inc. (NYSE: ADT) will replace Arrowhead Pharmaceuticals in the S&P SmallCap 600 effective prior to the opening of trading on Monday, February 9. Thoma Bravo L.P. acquired Dayforce in a deal that closed today.
• OneSpaWorld Holdings Ltd. (NASD: OSW) will replace Dynavax Technologies Corp. (NASD: DVAX) in the S&P SmallCap 600 effective prior to the opening of trading on Tuesday, February 10. Sanofi is acquiring Dynavax Technologies in a deal expected to be completed soon pending final closing conditions.

Following is a summary of the changes that will take place prior to the open of trading on the effective date:

Effective Date	Index Name	Action	Company Name	Ticker	GICS Sector
Feb 9, 2026	S&P 500	Addition	Ciena	CIEN	Information Technology
Feb 9, 2026	S&P 500	Deletion	Dayforce	DAY	Industrials
Feb 9, 2026	S&P MidCap 400	Addition	Arrowhead Pharmaceuticals	ARWR	Health Care
Feb 9, 2026	S&P MidCap 400	Deletion	Ciena	CIEN	Information Technology
Feb 9, 2026	S&P SmallCap 600	Addition	ADT	ADT	Consumer Discretionary
Feb 9, 2026	S&P SmallCap 600	Deletion	Arrowhead Pharmaceuticals	ARWR	Health Care
Feb 10, 2026	S&P SmallCap 600	Addition	OneSpaWorld Holdings	OSW	Consumer Discretionary
Feb 10, 2026	S&P SmallCap 600	Deletion	Dynavax Technologies	DVAX	Health Care

ABOUT S&P DOW JONES INDICES

S&P Dow Jones Indices is the largest global resource for essential index-based concepts, data and research, and home to iconic financial market indicators, such as the S&P 500® and the Dow Jones Industrial Average®. More assets are invested in products based on our indices than products based on indices from any other provider in the world. Since Charles Dow invented the first index in 1884, S&P DJI has been innovating and developing indices across the spectrum of asset classes helping to define the way investors measure and trade the markets.

S&P Dow Jones Indices is a division of S&P Global (NYSE: SPGI), which provides essential intelligence for individuals, companies, and governments to make decisions with confidence. For more information, visit www.spglobal.com/spdji/en/. 

FOR MORE INFORMATION:

S&P Dow Jones Indices
index_services@spglobal.com

Media Inquiries
spdji.comms@spglobal.com

View original content:https://www.prnewswire.com/news-releases/ciena-set-to-join-sp-500-arrowhead-pharmaceuticals-to-join-sp-midcap-400-adt-and-onespaworld-holdings-to-join-sp-smallcap-600-302679569.html

SOURCE S&P Dow Jones Indices

FAQ

When will ADT (ADT) join the S&P SmallCap 600?

ADT will join the S&P SmallCap 600 prior to the opening of trading on Feb 9, 2026. According to S&P Dow Jones Indices, this is part of a scheduled rebalancing affecting multiple indexes and takes effect at the market open on that date.

Why was Dayforce (DAY) removed from the S&P 500 on Feb 9, 2026?

Dayforce was removed from the S&P 500 because Thoma Bravo completed an acquisition of Dayforce. According to S&P Dow Jones Indices, the deal closed and the company no longer met index inclusion criteria, prompting the deletion effective Feb 9, 2026.

What does Ciena's (CIEN) addition to the S&P 500 mean for investors?

Ciena's addition places CIEN in the S&P 500 effective Feb 9, 2026, which may increase passive fund demand. According to S&P Dow Jones Indices, index inclusion typically prompts reweighting by index-tracking funds at the open on the effective date.

How does Arrowhead Pharmaceuticals (ARWR) moving to the S&P MidCap 400 affect its index status?

Arrowhead will be added to the S&P MidCap 400 and removed from the S&P SmallCap 600 prior to trading on Feb 9, 2026. According to S&P Dow Jones Indices, the change reflects index reconstitution and will alter which funds track ARWR.

When does OneSpaWorld (OSW) join the S&P SmallCap 600 and what is the effective date?

OneSpaWorld will join the S&P SmallCap 600 effective prior to the opening of trading on Feb 10, 2026. According to S&P Dow Jones Indices, OSW replaces Dynavax in the SmallCap 600 on that effective date.

Was the Dynavax (DVAX) removal tied to a transaction, and what is the timing?

Dynavax was deleted from the S&P SmallCap 600 effective Feb 10, 2026 ahead of a pending acquisition by Sanofi. According to S&P Dow Jones Indices, the removal aligns with the announced transaction awaiting final closing conditions.