The swine flu is back in Australia as it infects those who are young and healthy with a vengeance. Reports said more than 21,000 Australians were affected with the H1N1 virus within the year as cases increased by 36 per cent compared to same period in 2013.

Health experts warned that the deadly swine flu is a "predominant strain" and has claimed the lives of 1,600 Australians in 2009. Records reveal Queensland as the state with the highest number of swine flu cases at 6,890 up to August 12. NSW reported 6,652 cases while Victoria had 2,715 H1N1 cases.

Swine flu began sweeping Australia during the first two months of 2014 with more than 2,500 cases reported which is already five times more than the usual. Experts said people aged 24 to 64 had the highest risk of death from H1N1 infection. Reports said 60 per cent of the people who belong to that age group had died from swine flu in the United States.

Influenza Specialist Group chairman Dr Alan Hampson said one-third of those with severe cases of swine flu are young adults. He added that the number of flu cases is expected to climb higher than laboratory-tested cases since only patients with severe symptoms are tested.

More than two thirds of the flu viruses sent to laboratories were found to be the H1N1 virus, also known as swine flu. According to experts, the H3N2 flu strain is common in NSW with the elderly being the most afflicted.

Hampson urged Australians to get vaccinated because there may still be a narrow window for protection. Young girls from teenagers to their mid-forties are vulnerable to swine flu since doctors have discovered the virus interacting more with female hormones.

The flu season is expected to end in October but Hampson warned it could extend through the summer in some cases. The H1N1 virus thrives in the winter with more people susceptible to flu during the cold season. The cold weather can cause irritation in the respiratory tract. A Vitamin D deficiency can also weaken the human body's immune system because of lack of sunlight.

Australians are encouraged to always keep hands clean by observing proper handwashing techniques and avoiding large crowds to help prevent swine flu.