A Canadian teenager who contracted the H5N1 bird flu in November has fully recovered after battling severe illness that required intensive care and advanced life support. However, genetic analysis of the virus revealed troubling mutations that may increase its ability to target human cells and cause severe disease, researchers reported in a special edition of the New England Journal of Medicine.

The 13-year-old girl initially presented at an emergency room with pink eye, fever, and a history of asthma and obesity. After her symptoms worsened, including respiratory distress and pneumonia, she was transferred to a pediatric intensive care unit. Her condition escalated to respiratory failure, requiring intubation and extracorporeal membrane oxygenation (ECMO), a life support technique.

Doctors treated her with a combination of antiviral drugs and plasma exchange therapy to combat a potentially lethal cytokine storm. Despite the severity of her illness, she began to recover after eight days and was discharged later in November.

Genetic sequencing of the virus revealed it was the D1.1 strain of H5N1, commonly found in wild birds but distinct from strains circulating in commercial poultry and dairy cows that have caused most human infections in the U.S. The virus exhibited mutations linked to improved replication in human cells, raising concerns about its potential to cause more severe infections.

Researchers noted that similar mutations were found in a Louisiana patient with severe H5N1 disease, suggesting these genetic changes may arise during replication in human hosts rather than being present in the wild.

Dr. Jennifer Nuzzo, director of the Pandemic Center at Brown University, described the findings as alarming. “While these mutations may not be circulating widely in the environment, they suggest that the virus can adapt in humans, potentially leading to more severe outcomes,” she said.

With 66 human cases of H5N1 reported in the U.S. in 2024 alone, experts warn of the virus’s potential to cause serious illness. “This is not a virus to take lightly,” Nuzzo emphasized.