A fifth of the global population was infected with swine flu during the 2009-2010 pandemic, with nearly half of them children, a new study by the WHO reveals. But despite extensive fears, it proved less deadly people than seasonal flu. The WHO's report found that between 20 and 27 per cent of people worldwide caught the H1N1 virus, commonly known as swine flu, during that period. The study revealed that those aged between five and 19 showed the greatest rate of infection, with around forty-seven per cent suffering.In contrast around 11 per cent of people aged 65 and over were infected with the virus. To draw such conclusions researchers from the World Health Organization (WHO) and Imperial College London examined 90,000 blood samples collected during and after the pandemic from as many as 19 countries where the disease was present. The study, published in the journal Influenza and Other Respiratory Viruses, is based on data from published and unpublished H1N1 seroepidemiological studies, scientists explained.