Apellis Stock Soars 140% on $5.6B Biogen Takeover Deal

Biogen Announces Landmark Acquisition of Apellis

Biogen Inc. has entered into a definitive agreement to acquire Apellis Pharmaceuticals Inc. in a deal valued at approximately $1.6 billion. The announcement, made on March 31, 2026, sent shares of Apellis (NASDAQ: APLS) soaring by as much as 140% in pre-market trading, marking one of the most significant moves in the biotech sector this year. The acquisition underscores Biogen's strategy to diversify its revenue streams and strengthen its portfolio in immunology and rare diseases.

Terms of the Acquisition

Under the terms of the all-cash transaction, Biogen will acquire all outstanding shares of Apellis for $11.00 per share. This price represents a substantial premium of approximately 140% over Apellis's closing price on the previous trading day, which was near $17.10. The deal provides immediate and significant value to Apellis shareholders, who had seen the stock trade under pressure in recent months.

In addition to the upfront cash payment, the agreement includes a non-transferable contingent value right (CVR). This CVR entitles Apellis shareholders to receive two potential future payments of $1.00 each, for a total of up to $1.00 per share. These payments are contingent on Syfovre, a key Apellis drug, achieving certain global annual net sales thresholds. If fully realized, the CVRs would bring the total potential value for shareholders to $15.00 per share.

Market Reacts Swiftly

The market response was immediate and dramatic. Apellis stock surged to a new two-year high, reaching an intra-day peak of $10.45 before closing the day up 135.40% at $10.23. Trading volume exceeded 33 million shares, among the highest in the company's history for a single session. This sharp increase reflects strong investor approval of the acquisition premium and the strategic logic of the merger.

Conversely, shares of the acquirer, Biogen (NASDAQ: BIIB), declined following the announcement. Biogen's stock fell by nearly 7% in pre-market trading, a typical reaction for a company paying a significant premium in a large acquisition. The move reflects investor calculations regarding the financial outlay and integration risks associated with the deal.

Strategic Rationale for Biogen

This acquisition is a key component of Biogen's ongoing transformation strategy. The company has been seeking to offset declining revenues from its established multiple sclerosis franchise and navigate the slow market adoption of its Alzheimer's treatment. By acquiring Apellis, Biogen gains access to a portfolio of commercialized and high-growth assets in immunology, rare diseases, and nephrology.

Biogen CEO Christopher A. Viehbacher stated that the deal immediately advances the company's transformation and expands its growth portfolio. Apellis CEO Cedric Francois added that Biogen's experience in immunology and rare diseases will accelerate the impact of Apellis's innovations and help reach more patients.

Financial Impact and Key Assets

The acquisition adds two approved, revenue-generating medicines to Biogen's portfolio: Syfovre and Empaveli. Together, these two treatments achieved combined net sales of $189 million in 2025. The companies project this revenue to grow at a mid-to-high teens percentage rate annually at least through 2028.

Syfovre is the first and only FDA-approved therapy for geographic atrophy (GA) secondary to age-related macular degeneration, a leading cause of blindness. Empaveli is approved for treating rare kidney diseases and a rare blood disorder. These assets provide Biogen with an immediate boost to its top line. Biogen expects the transaction to be increasingly accretive to its non-GAAP diluted earnings per share (EPS) starting in 2027 and to meaningfully increase its EPS growth rate through the end of the decade.

Summary of Deal Metrics

Path to Completion

The transaction is expected to close in the second quarter of 2026. The completion is subject to customary closing conditions, including approval from Apellis shareholders and the satisfaction of regulatory requirements. Biogen plans to finance the acquisition through a combination of cash on hand and borrowings, stating it expects to de-lever by the end of 2027 while maintaining financial flexibility for future investments.

Conclusion

The acquisition of Apellis Pharmaceuticals by Biogen marks a significant strategic move that reshapes parts of the biotech landscape. For Apellis shareholders, the deal delivers a substantial and immediate return. For Biogen, it accelerates a strategic pivot toward high-growth areas, though the market has signaled caution regarding the premium paid. The focus will now turn to a smooth integration and the market performance of Syfovre and Empaveli to realize the full long-term value of the transaction.