What is the H3N2 flu strain: Causes, symptoms and prevention

As the winter season grips India and other parts of the world, health officials are sounding the alarm about the spread of H3N2 influenza, a subtype of the influenza A virus that has been responsible for many seasonal flu epidemics. Caused by the influenza A virus, H3N2 reportedly infects 10-20% of people worldwide each year, making it a significant public health concern.

The virus, which made its first jump to humans in 1968 through antigenic shift with avian strains, has evolved over the years to become a major cause of flu hospitalisations, particularly among vulnerable populations such as children under 5 and adults over 65.

In severe seasons, H3N2 can account for up to 50% of flu hospitalisations, with complication rates 2-5 times higher than those of the milder H1N1 strain. In India, the virus has already shown 20% positivity rates in recent months, tied to crowded homes and less sun.

Health experts warned that the UK may have its most severe flu outbreak in decades this winter, fuelled by the H3N2 strain. Hospital admissions for flu have already increased by 56% over last year, with rates seven times greater than in 2023, and the peak is still to come, according to the Independent.

How H3N2 Works

H3N2 is a highly contagious virus that wraps its genetic material in a fatty coat with spike proteins termed hemagglutinin (H3), which stick to cells in the nose and throat. Following this, it slides inside, tricking the cell into producing virus copies before bursting out to infect surrounding cells.

According to a 2018 study by Henslet, modern H3N2 has added sugary shields that allow it to avoid your immune system while gripping onto human cells more tightly. One infected cell produces thousands more in hours.

Symptoms to Watch Out For

The symptoms of H3N2 influenza are similar to those of other flu strains, including fever, dry cough, sore throat, body aches, and fatigue. However, H3N2 is known to cause more severe illness, with fever reaching up to 38-40°C in 70% of cases, a dry cough present in 90% of cases and sore throat in 50% cases. Body aches, loss of appetite and fatigue are also common, and the virus can also lead to pneumonia in a few cases.

Prevention

Preventing H3N2 influenza involves a multi-pronged approach, which is crucial as the virus spreads via droplets and surfaces, including annual flu vaccination, diligent handwashing, wearing masks in crowds, practicing respiratory etiquette (coughing/sneezing into elbow), social distancing, boosting immunity with a healthy diet/sleep/exercise, ensuring good ventilation, and avoiding self-medication.

Vulnerable populations, such as children under 5 and adults over 65, should be especially careful, as they are at higher risk of hospitalisation.

“It’s not inevitable that flu spreads through a household – though it’s highly likely. If you’ve got proper flu, you’re unlikely to be leaving the house anyway. It’s not the same as just having a heavy cold," Dr Simon Clarke, an associate professor in cellular microbiology at the University of Reading, was quoted as saying by The Telegraph.

He added that there was no such thing as a magic bullet. But the basics do the work: handwashing, avoiding large indoor events, staying home when sick, and self-isolation within families where possible, he said.