NEW YORK — A patient being treated with Pfizer Inc’s (PFE.N) hemophilia drug, Hympavzi, as part of a long-term study died after experiencing serious side effects, the company said.

The individual passed away on December 14 following a stroke and subsequent brain hemorrhage, according to the European Haemophilia Consortium, a patient support group. The patient was enrolled in a study evaluating Hympavzi in people with hemophilia A or B, with or without inhibitors.

“Pfizer, together with the trial investigator and the independent external Data Monitoring Committee, are actively gathering information to better understand the complex, multi-factorial circumstances surrounding this occurrence,” the company said in a statement.

Hympavzi, a once-weekly injection, gained U.S. approval last year to prevent or reduce bleeding episodes in hemophilia patients aged 12 and older by targeting blood-clotting proteins. Based on current knowledge and overall clinical data, Pfizer does not anticipate any impact on patient safety, the company added.

People with hemophilia have genetic defects that disrupt clotting factor production, leading to spontaneous and severe bleeding after injuries or surgery. Earlier this year, Pfizer announced it would halt global development of its hemophilia gene therapy, Beqvez, citing soft demand from patients and doctors. Beqvez had been approved in the U.S. for adults with moderate to severe hemophilia B.