‘Worrying’ mutations found in H5N1 bird flu virus in Canadian teenager

The fate of a Canadian teenager who was infected with H5N1 bird flu in early November and subsequently admitted to an intensive care unit has finally been revealed: She has made a full recovery.

But genetic analysis of the virus that infected her body revealed ominous mutations that researchers suggest potentially made it easier to target human cells and cause severe disease — a development the study’s authors called “worrying.”

The case was published Tuesday in a special issue of the New England Journal of Medicine that explored H5N1 cases from 2024 in North America. In a study, doctors and researchers who worked with the Canadian teenager published their findings. In the second, public health officials from across the United States — from the Centers for Disease Control and Prevention, as well as state and local health departments — chronicled the 46 human cases that occurred between March and October.

There has been everything 66 reported human cases of H5N1 bird flu in the United States in 2024.

In the case of the 13-year-old Canadian child, the girl was admitted to a local emergency room on November 4 after suffering two days of conjunctivitis (pink eye) in both eyes and a day of fever. The child, who had a history of asthma, an elevated body mass index and grade 2 obesity, was discharged that day without treatment.

Over the next three days, she developed a cough and diarrhea and started vomiting. She was brought back to the emergency room on Nov. 7 in respiratory distress and with a condition called hemodynamic instability, in which her body was unable to maintain consistent blood flow and pressure. She was admitted to the hospital.

On November 8, she was transferred to a pediatric intensive care unit at another hospital with respiratory failure, left lower lung pneumonia, acute kidney injury, thrombocytopenia (low platelet count), and leukopenia (low white blood cell count).

She tested negative for the predominant human seasonal flu viruses – but had a high viral load of influenza A, which includes the major human seasonal flu viruses, as well as H5N1 bird flu. This finding prompted her caregivers to test for bird flu; she tested positive.

As the disease progressed over the next few days, she was intubated and put on extracorporeal membrane oxygenation (ECMO) — a life support technique that temporarily takes over the function of the heart and lungs for patients with severe heart or lung disease.

She was also treated with three antiviral drugs, including oseltamivir (brand name Tamiflu), amantadine (Gocovri), and baloxavir (Xofluza).

Because of concerns about the potential for a cytokine storm — a potentially fatal condition in which the body releases too many inflammatory molecules — she was put on a daily regimen of plasma exchange therapy, in which the patient’s plasma is removed in exchange for donated healthy plasma.

As the days passed, her viral load began to decline; on November 16, eight days after being hospitalized, she tested negative for the virus.

However, the authors of the report noted that the viral load consistently remained higher in her lower lungs than in her upper airways—suggesting that the disease can manifest in places not currently tested for it (like the lower lungs), even though it disappear from those tested (such as mouth and nose).

She made a full recovery and was discharged sometime after November 28, when her intubation tube was removed.

Genetic sequencing of the virus circulating in the teenager showed that it was similar to the one circulating in wild birds, the D1.1 version. It is a type of H5N1 bird flu that is related but different from the type that circulates in dairy cows and is responsible for the vast majority of human cases reported in the United States — most of which were acquired via dairy cows or commercial poultry. This is also the same version of the virus that was found in a Louisiana patient who experienced a serious illness, and it showed a few mutations that the researchers say increase the virus’s ability to replicate in human cells.

In the Louisiana case, researchers from the CDC suggested that the mutations arose as they replicated in the patient and were probably not present in nature.

Regardless of where and when they originated, said Jennifer Nuzzo, director of the Pandemic Center at Brown University in Providence, RI, “it’s concerning because it indicates that the virus can change in a person and possibly cause a greater severity of symptoms than originally . infection.”

In addition, Nuzzo — who was not involved in the research — said while there is evidence that these mutations arose after the patients were infected and therefore are not circulating in the environment, “it raises the concern that some people may experience more severe infection than other people. The bottom line is that this is not a good virus to get.”