Biogen has prevailed in a patent squabble with Denmark’s Forward Pharma over multiple sclerosis med Tecfidera—but the decision may not actually help the Big Biotech steer clear of generic rivals. The Patent Trial and Appeal Board (PTAB) ruled Friday that Forward could not declare patent infringement by Biogen. The verdict kept Biogen’s Tecfidera IP intact and secured exclusivity through 2028. It’s an outcome that is worth about $5 of upside to Biogen’s stock, Mizuho analyst Salim Syed and Leerink Partners analyst Geoffrey Porges wrote to their respective clients. In January, Biogen hedged the outcome of the Forward challenge by agreeing to a $1.25 billion settlement with the Danish pharma. The deal would have allowed it to license Forward’s IP to shield Tecfidera had the PTAB ruling not gone its way.

Biogen’s patent

The way Bernstein analyst Ronny Gal saw it, though, Biogen may have been better off going with Forward’s patent instead of its own. Biogen’s patent, in his view, “is relatively weak,” and he thought it stood just a roughly 50% chance of holding up against ANDA challengers that recently got the green light to file.

“We think Tecfidera is more at risk now that they won the battle against Forward Pharma, and not the other way around,” Gal said in an investor video.

Both Porges and Syed said they expect those generic challengers—whose FDA filing window opened on March 27—to show up. And, like Gal, Porges cautioned that “we still believe there is a high likelihood that the patent is invalidated in U.S. patent courts by generic filers.”

Why? Though the patent set to protect the blockbuster from 2021 to 2028 has won a couple boosts as of late—both the interference andshut-down of patent challenger Kyle Bass at the PTAB—the fact that it’s alone in Biogen’s portfolio represents a problem, Porges said.

“This single patent will provide a targeted and specific path to invalidation by generic filers, and if invalidated, would allow generic manufactures to launch without the risk of potential infringement on ancillary patents,” he wrote.