Sanofi SA (SNY) announced Wednesday that it's paying $2.2 billion to acquire Dynavax Technologies Corporation (DVAX), shelling out $15.50 per share in cash as it doubles down on adult vaccines.

The move significantly expands Sanofi's footprint in adult immunization, a market the French pharmaceutical company has been keen to dominate. And it's not just buying pipeline dreams—Dynavax comes with a commercially available vaccine already generating revenue.

What Sanofi Is Actually Getting

The star of the acquisition is HEPLISAV-B, Dynavax's adult hepatitis B vaccine that's currently sold in the United States. What makes it interesting is the convenience factor: it's a two-dose regimen administered over just one month, compared to the traditional three-dose schedule spread across six months that other hepatitis B vaccines require.

That shorter timeline means patients achieve high levels of seroprotection faster, which matters when you're trying to get people to actually complete their vaccination series. Anyone who's tried to remember to show up for shot number three six months later knows why this is a selling point.

But Sanofi isn't just buying what's already on pharmacy shelves. The deal also includes Z-1018, Dynavax's shingles vaccine candidate currently in phase 1/2 clinical development, along with additional vaccine pipeline projects that could pan out down the road.

"Dynavax enhances Sanofi's adult immunization presence by adding differentiated vaccines that complement Sanofi's expertise," said Thomas Triomphe, Executive Vice President of Vaccines at Sanofi.

How Sanofi Plans to Pay

Sanofi will fund the acquisition using cash on hand, which shouldn't be much of a stretch. The company reported 8.906 billion euros—roughly $9.7 billion—in cash and cash equivalents for the quarter ending September 30, 2025. So writing a $2.2 billion check won't require any creative financing.

The deal isn't expected to affect Sanofi's financial guidance for 2025 and should close in the first quarter of 2026, assuming the usual regulatory hoops get cleared.

Meanwhile, an MS Drug Setback

In less cheerful news for Sanofi, the FDA issued a complete response letter on Thursday for tolebrutinib, the company's experimental treatment for non-relapsing secondary progressive multiple sclerosis in adults. A complete response letter is FDA-speak for "not approved"—the agency has concerns that need addressing before it'll give the green light.

This wasn't entirely surprising. Back on December 15, 2025, Sanofi had already warned that the FDA review would extend beyond the revised December 28, 2025 target action date, with further guidance expected by the end of the first quarter of 2026.

Following an FDA request, the company confirmed it has submitted an expanded access protocol for tolebrutinib, which would allow certain patients to access the drug before formal approval.

Sanofi is also conducting an impairment test under international accounting standards on the intangible asset value tied to tolebrutinib, with results expected when the company reports fourth quarter and full-year 2025 results in January 2026. The company emphasized that the outcome won't impact business net income or business earnings per share, and there's no change to its 2025 financial guidance.

Market Reaction

Sanofi shares slipped 0.14% to $48.25 in premarket trading Wednesday, while Dynavax stock rocketed up 37.47%—which makes sense when someone offers to buy you at a hefty premium to your recent trading price.