This Biotech Stock Soars 39%. Sanofi Is Buying It for $2.2 Billion.

Dynavax shareholders will receive $15.50 a share in the all-cash deal. (Gonzalo Fuentes/POOL/AFP via Getty Images)

Key Points

• Sanofi will acquire Dynavax Technologies for $2.2 billion in an all-cash deal, with shareholders receiving $15.50 per share.
• Dynavax shares surged 39% to $15.42 following the announcement, while Sanofi’s U.S.-listed depositary receipts declined less than 0.1%.
• The acquisition includes Dynavax’s HEPLISAV-B adult hepatitis B vaccine and a shingles vaccine candidate in early-stage trials.

Sanofi has agreed to acquire vaccine maker Dynavax Technologies in an all-cash deal worth $2.2 billion in total equity value.

Dynavax shareholders will receive $15.50 a share in the deal, a premium on the stock’s closing price of $11.13 on Tuesday. The acquisition is expected to close in the first quarter of 2026, the companies said.

Shares of Dynavax spiked 39% to $15.42 on Wednesday. U.S.-listed depositary receipts of Sanofi, which is based in France, were down less than 0.1% to $48.29.

Sanofi will get Dynavax’s adult hepatitis B vaccine, HEPLISAV-B, in the deal. The shot is already marketed in the U.S. and requires two doses over one month, which quickens seroprotection compared to hepatitis B vaccines that are delivered in three doses over six months.

Dynavax is also developing a shingles vaccine candidate (Z-1018), which is currently in early-stage clinical trials.

“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.

Sanofi last year agreed to work with Novavax on selling its Covid-19 vaccine in the U.S. The pair completed the marketing transfer last month.

Wednesday’s deal is likely a welcome early Christmas gift for Dynavax shareholders. The stock had tumbled 13% in 2025, through Tuesday. The biotech company is pace to swing to a loss this year after posting a profit in 2024.

Write to Nate Wolf at nate.wolf@barrons.com