Almost half of UK children hit by swine flu virus

Overall, at least a fifth of the general population was infected. But death rates were low – at less than 0.02 per cent.

The new figures are from an international study looking at the 2009 H1N1 swine flu pandemic in 19 countries, including the UK, US, India and China. Children and young people showed the highest rates of infection, according to the findings, with 47 per cent of those aged five to 19 developing symptoms. In contrast, only 11 per cent of people aged 65 and older caught the flu.

Multiple exposures to previously circulating flu viruses may have given older people some immune protection, said researchers.

Blood samples taken before the pandemic showed that 14 per cent of the over-65s had antibodies that reacted to the 2009 strain.

The study, led by experts from the World Health Organisation (WHO) and Imperial College London, is published in the journal Influenza and Other Respiratory Viruses. Scientists pooled the results of around two dozen research papers. Dr Anthony Mounts, from the WHO, said: “Knowing the proportion of the population infected in different age groups and the proportion of those infected who died will help public health decision-makers plan for and respond to pandemics.”