Babies and children * Young people

Child swine flu 10 times higher than thought

Zone default image Many children without symptoms

Swine flu infection rates in children were ten times higher than estimated during the first wave of the pandemic, research published today has shown.

Estimates of the number of swine flu cases during the first wave of the pandemic in England were based on the number of people visiting their GP with influenza-like illness. People with mild or no symptoms would not have counted.

Researchers from the UK Health Protection Agency tested two sets of blood samples for immunity to the H1N1 virus. The first group of samples were taken before the pandemic started. The second set of blood samples were taken in August and September 2009, after the first wave of the pandemic.

The results show that the highest infection rates occurred in London and the West Midlands, and confirmed reports during the outbreak that young people were most affected by swine flu.

Before the swine flu outbreak, only 1.8% of children under the age of four had immunity to the virus, but by September 2009, this increased to 21.3%.

Children between the ages of five and 14 were hardest hit, as 42% had antibodies to the H1N1 virus by September 2009 compared with just 3.7% before the outbreak began.

In the study, published in the Lancet online, the authors stated: “Rates of infection with 2009 pandemic H1N1 influenza in the first wave were greatest in children younger than 15 years of age, with an estimated 42% of schoolchildren aged 5–14 years being infected in high incidence regions.

"This finding is consistent with the high level of susceptibility in children and the increased potential for transmission that occurs within schools. We also showed substantial differences between regions in the extent of infection during the first wave.”

The research team also added that the infection rates for London were 10 times higher than the original estimates based on GP reports, saying: “This serological study shows the true extent of H1N1 infection in the initial wave of the pandemic in England in 2009. Its findings should be applicable to other countries that have experienced a similar first wave.”

This article was published on Thu 21 January 2010

Image © CDC C. S. Goldsmith and A. Balish

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