New Year’s Eve in 2019 was the ominous farewell to the year. On this day, the WHO’s office in China brought reports of a ‘viral pneumonia’ to light. The first news articles regarding this disease hardly filled an unassuming column in the newspapers. It was preposterous to think it would become something far worse. By the next New Year’s Eve, this disease garnered attention in every nook and cranny of esteemed dailies. COVID-19 has reshaped our lives since then.
Now, there’s another unassuming virus, which is lying in the shadows, while one of its kin is taking the spotlight. The kin is none other than the avian influenza virus H5N1, which has wreaked havoc by infecting and killing poultry and dairy cows. It has also killed 21 people since 2020. This virus is undoubtedly a global concern, but H9N2 —the virus that’s keeping a low profile —is much better suited to infect humans, causing only minor disease in birds.
H9N2 has received very little attention despite being the second-most-common strain of avian influenza that can affect humans. The virus has infected 173 people since 1998, and most cases have occurred in China.
H9N2 might be more prevalent than we realize, says Michelle Wille, who studies bird flu at the Peter Doherty Institute for Infection and Immunity in Melbourne. The reason H9N2 is not in the limelight is its cousin: most cases of avian influenza infection in humans are attributed to H5N1, with almost no testing for H9N2. This virus also causes a mild infection that generally requires no hospitalization.
The H9N2 virus underwent genetic changes in 2015, which made it more infectious. In 2024, a version of this virus infected more human cells than a historical sample from 1999 did. The mutations have also enhanced the virus’s binding capacity to human cell receptors, making it even more potent in causing an infection.
Increased surveillance is required, but there lies a significant caveat. Countries are not required to report cases of infection caused by low-pathogenic pathogens. Screening mammals in proximity to birds and poultry for this virus is also needed. Fears of genetic mixing within the cells of animals infected with multiple viruses, leading to the generation of a completely new strain, are on the rise. These hybrid viruses could pose a serious threat if they infect humans. In fact, genetic material that supposedly came from the H9N2 virus has been found in other viruses responsible for avian influenza outbreaks.
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