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http://www.forexyard.com/en/news/UK-chi ... 21T000104Z

UK child H1N1 flu rate was much higher than thought

One child in three caught the pandemic H1N1 flu in the first wave of infection in hard-hit areas of England in 2009 -- up to 10 times more than originally thought, scientists said on Thursday.

Blood samples suggest children are central to flu's spread and should be a key target group for vaccination, experts from Britain's Health Protection Agency (HPA) wrote in the study in The Lancet medical journal.

"This...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," they said.

[...]


But these did not account for mild cases, those that had no symptoms or those who opted not to see a doctor, the HPA said.

For their study, the scientists used around 1,400 blood serum samples taken in 2008 as a base line and compared them with more than 1,900 serum samples taken in August and September 2009, after the first British wave of H1N1 infection.

They found that rates of infection in the first wave were greatest in children under 15, with an estimated 42 percent of schoolchildren aged 5 to 14 years infected in high incidence areas like London and parts of central England.

The blood sample data also showed the child infection rate for the British capital, where 32 percent of under 15s were infected, was 10 times higher than original HPA estimates.

Tex, maybe you should post this into the other toipc you created before (absence of a respiratory epidemic in midwinter is inexplicable) - because this is a reasonable explanation for the inexplicable absence of a respiratory epidemic in midwinter,,, If most have antibodies...

The Lancet, Early Online Publication, 21 January 2010doi:10.1016/S0140-6736(09)62126-7Cite or Link Using DOIIncidence of 2009 pandemic influenza A H1N1 infection in England: a cross-sectional serological study
Original Text
Prof Elizabeth Miller FRCPath a , Katja Hoschler PhD b, Pia Hardelid PhD c, Elaine Stanford BSc [Hons] d, Nick Andrews MSc c, Prof Maria Zambon PhD b
Summary
Background
Knowledge of the age-specific prevalence of immunity from, and incidence of infection with, 2009 pandemic influenza A H1N1 virus is essential for modelling the future burden of disease and the effectiveness of interventions such as vaccination.
Methods
In this cross-sectional serological survey, we obtained 1403 serum samples taken in 2008 (before the first wave of H1N1 infection) and 1954 serum samples taken in August and September, 2009 (after the first wave of infection) as part of the annual collection for the Health Protection Agency seroepidemiology programme from patients accessing health care in England. Antibody titres were measured by use of haemagglutination inhibition and microneutralisation assays. We calculated the proportion of samples with antibodies to pandemic H1N1 virus in 2008 by age group and compared the proportion of samples with haemagglutination inhibition titre 1:32 or more (deemed a protective response) before the first wave of infection with the proportion after the first wave.
Findings
In the baseline serum samples from 2008, haemagglutination inhibition and microneutralisation antibody titres increased significantly with age (F test p<0·0001). The proportion of samples with haemagglutination inhibition titre 1:32 or more ranged from 1·8% (three of 171; 95% CI 0·6—5·0) in children aged 0—4 years to 31·3% (52 of 166; 24·8—38·7) in adults aged 80 years or older. In London and the West Midlands, the difference in the proportion of samples with haemagglutination inhibition titre equal to or above 1:32 between baseline and September, 2009, was 21·3% (95% CI 8·8—40·3) for children younger than 5 years of age, 42·0% (26·3—58·2) for 5—14-year-olds, and 20·6% (1·6—42·4) for 15—24-year-olds, with no difference between baseline and September in older age groups. In other regions, only children younger than 15 years showed a significant increase from baseline (6·3%, 1·8—12·9).
Interpretation
Around one child in every three was infected with 2009 pandemic H1N1 in the first wave of infection in regions with a high incidence, ten times more than estimated from clinical surveillance. Pre-existing antibody in older age groups protects against infection. Children have an important role in transmission of influenza and would be a key target group for vaccination both for their protection and for the protection of others through herd immunity.
Funding
National Institute for Health Research Health Technology Assessment Programme.

http://www.thelancet.com/journals/lance ... 40-6736(09)62126-7/fulltext

I find it interesting that a pre-existing (before pH1N1) antibody protected the elderly against infection better than antibodies acquired from first pH1N1 infections. With what I've been reading about re-infections, at least this seems so.

Commentary

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