Dynamax Stock Soars Nearly 40% Today: Here’s Why It’s Flying

Dynamax shares just ripped through the market—up nearly 40% in a single session. The surge isn't random; it's a classic case of momentum meeting a catalyst.

The Numbers Don't Lie

A near-40% single-day gain doesn't happen on whispers. The move points to a significant, market-moving development—likely a major partnership, a breakthrough product announcement, or financial results that smashed even the most bullish estimates. When a stock flies this high, this fast, it's because institutional and retail money are piling in simultaneously.

Beyond the Headline Hype

This kind of explosive move often triggers a chain reaction. Analysts scramble to upgrade price targets, short sellers get squeezed, and the stock grabs the spotlight on every financial news feed. It becomes a self-fulfilling prophecy of attention and liquidity—at least for the short term. The real test is what comes after the pop.

Is This Sustainable or Just Another Pump?

The brutal truth? A one-day rocket ship tells you nothing about long-term trajectory. For every stock that uses a 40% surge as a launchpad, another fizzles out once the day-traders cash their chips. The coming days will separate the signal from the noise—watch for follow-through buying or a swift pullback. After all, on Wall Street, what goes vertical can often come down just as fast. It's the oldest story in finance: euphoria today, reality tomorrow.

Key Takeaways

• Sanofi will pay $2.2 billion for Dynavax Techologies as it looks to add another Hepatitis B and new shingles vaccines to its portfolio.
• The deal will pay Dynavax investors $15.50 per share, a 39% premium from Tuesday's closing price.

Shares of Dynavax Technologies (DVAX) skyrocketed after French drugmaker Sanofi (SNY) said it WOULD buy the biopharmaceutical firm for $2.2 billion to expand its Hepatitis B offerings and enter the shingles vaccine market.

Sanofi said it would be paying Dynavax investors $15.50 per share in cash, a 39% premium to its closing price yesterday. Dynavax shares were recently trading just a few cents below Sanofi's price for its shares. The transaction is expected to close in the first quarter of next year. 

Why This Matters to Investors

One strategy of drug-development investors is to buy shares of companies they think are candidates for a buyout by bigger companies who either think they can help their products find larger markets, or believe their developmental treatments will soon prove more valuable as they MOVE through testing.

Dynavax currently has regulatory approval for its Heplisav-B Hepatitis B shot, a two-dose regimen for adults given over a month’s time. It also is in a Phase 1/2 trial of a shingles treatment called Z-1018, and has other candidates in the works. 

Thomas Triomphe, executive vice president of vaccines at Sanofi, said the additions of Heplisav-B and Z-1018 “bring new options to our portfolio and underscore our commitment to providing vaccine protection across the lifespan.”

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Sanofi said there is an “unmet need” for Hepatitis B and shingles treatments, as nearly 100 million people in the U.S. who were born before 1991 are unvaccinated. Dynavax CEO Ryan Spencer said the deal "will provide the global scale and expertise needed to maximize the impact of our vaccine portfolio."

Shares of Dynavax have spent most of 2025 in negative territory, but with today’s gains they’re now up about 19% year-to-date.