Second Bird Flu Strain; Should We Be Worried?
Image Courtesy: Alvesgaspar via Wikimedia Commons
H5N1 bird flu, a disease caused by the Influenza A virus, is frequently in the headlines as a virus with “pandemic potential”, due to its ability to spill over from birds into cows, and occasionally into humans. In early 2024, H5N1 raced through dairy herds in the US, and reportedly started spilling over into humans in North America not long after.
This isn't the first time that H5N1 has been reported in humans. In 1997, 18 poultry workers in Hong Kong became unwell after an avian flu outbreak, and 6 of them died. Since then, H5N1 has been on the radar of many virologists as a potential pandemic agent, but recent new mutations are beginning to cause alarm. According to Louise Moncla, a virologist from the University of Pennsylvania “this feels the closest to an H5 pandemic that I’ve seen”.
Scientists primarily focus on two strains of H5N1, B3.13, and now a new strain known as D1.1 which is in the same clade (a group with a single common ancestor) as B3.13. D1.1 was the main strain circulating in North American migratory birds in 2024, and was initially found in a herd of cattle in Nevada. These cases represent the only genotype to be reported in US dairy cattle other than B3.13. It also demonstrates the second known spillover from wild birds into dairy cattle.
Currently, only three infections in humans have been caused by D1.1, and there is no evidence to suggest that this strain is more dangerous than the other. That being said, one of the most severe cases was recorded in a Canadian teenager who, unlike other cases, had no connection to infected animals. The virus infecting the teenager was shown to contain two potential mutations that increased the virus’s ability to infect human cells. The teenager initially had an eye infection, which later became a severe lung infection. This may be good news, as it suggests that the virus might have evolved within the individual, and so the mutated form of the virus is not circulating in the population.
Headlines regarding this strain can be alarming, with words like ‘deadly’, ‘highly pathogenic’, and ‘lethal’ being commonplace. But, how much of a threat is this new strain?
The pandemic potential of H5N1 depends on its ability to mutate to allow person-to-person transmission. It is an ongoing debate between scientists whether or not this is likely to happen, as other avian flu viruses with pandemic potential have simply faded away.
The problem here is that many human infections with H5N1 may go undetected, which offers the virus a better opportunity to adapt to us. Comparatively to previous H5N1 clades, the clade currently circulating has been shown to be better at binding to cells in the human respiratory tract, suggesting an increased risk for adaptation and infection in humans.
Promisingly, stockpiles of vaccines which may be effective against H5N1 already exist, and scientists are continually developing and testing vaccines against circulating strains. Should the virus begin to spread more widely, vaccinating people to prevent the mixing of H5N1 with seasonal influenza viruses that are already well adapted to humans, would be key in preventing a pandemic.
COVID-19 somewhat caught the world by surprise. The pandemic taught scientists and public health professionals a harsh lesson, and for now, we must trust that we will be better prepared for the next - whatever that may be.