WASHINGTON - PEOPLE over the age of 50 who are hospitalised with H1N1 flu are the group most likely to die from the illness, but (A)H1N1 flu remains a young person's illness, US researchers said on Tuesday.

Around 11 per cent of the 1,088 cases of H1N1 flu reported in California between April 17 and Aug 22 died, and although infants were most likely to be hospitalised with (A)H1N1 influenza, the death rate was higher among older people, researchers at the California department of health said.

'Overall fatality was 11 per cent (118/1,088) and was highest (18-20 per cent) in persons aged 50 years or older,' the researchers wrote in the study, which will appear in Wednesday's issue of the Journal of the American Medical Association.

The death rate among children younger than 18 years, who made up around a third of H1N1 flu cases reported in California in the first 16 weeks of the outbreak, was seven percent, the study said.

US health officials have repeatedly characterised H1N1 flu as 'a younger person's disease' and put children and young adults under the age of 25 on a list of priority groups for vaccination against the disease.

More than half of hospitalisations and nearly a quarter of deaths in the United States from pandemic H1N1 have involved people under the age of 25. -- AFP