The "Aussie flu," or H3N2, is an influenza A virus that appears to cause more severe infection in the elderly and young children.

In the United States, the year's flu season is projected to be worse than last year's because of the dominance of this strain.

Vulnerable Group For Australian Flu

Health experts revealed one risk factor for this deadly strain: age. People who were born before the year 1968 are at higher risk of getting sick from the virus.

In Ireland, the rate of hospitalized flu patients between 55 and 64 years old is so far 8.4 per 100,000. The rate for patients between 35 and 44 years old is only 6.5 per 100,000. A similar trend is observed in Australia and the United States.

"The Australian experience showed that older people were more susceptible to the A(H3N2) strain of virus," said Jillian Johnston of England's Public Health Agency.

Why Age Matters

Experts explained that a person's odds of getting ill from a flu strain are partly influenced by the first type of virus they were exposed to as a child. Medical virologist Cillian De Gascun, head of National Virus Reference Laboratory at the University College Dublin, explained that a person's best immune response will be to viral infections that they contracted first.

"People born before 1968 would have been exposed to influenza A (H1N1) or A (H2N2) in their childhood," Gascun said. "As such, in simple terms their immunological memory response is probably suboptimal for A (H3N2)."

Older people also tend to produce less effective immune response compared with younger people.

"It has been recognized for many years that people 65 years and older are at greater risk of serious complications from the flu compared with young, healthy adults because human immune defenses become weaker with age," the U.S Centers for Disease Control and Prevention said.

Symptoms Of Australian Flu

H3N2 have similar symptoms associated with most flu but it can be more severe and infectious. It isn't exactly clear why H3N2 is more virulent than other flu strains but one possible reason is that it mutates faster than other viruses.

An aching body, sudden fever with a body temperature of 38C or above, feeling of tiredness and exhaustion, dry cough, sore throat, headache, diarrhea, and difficulty sleeping could be symptoms of flu.

Experts recommend vaccination for people 65 years and older because of their increased risk for complications from flu.

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