Children and teenagers are twice as likely to catch the A/H1N1 virus as adults aged 19-50, according to a study published in the New England Journal of Medicine.
The joint UK and US study examined how the virus spread among families in their own households and found that the transmissibility of this flu virus was lower than that seen in past pandemics.
Researchers from Imperial College London and a team from the US’s Centers for Disease Control and Prevention in Atlanta studied 816 people – made up of 216 patients with the virus and 600 household contacts.
They found that in the 216 homes observed, around 13% of people developed the infection after someone in their house had got it.
However, under 18-year-olds were found to be twice as likely as adults aged 19 to 50 to catch the virus, while people over the age of 50 were the least likely to develop it.
This is in line with current thinking that rates of swine flu have tended to be higher among younger age groups, hence the UK’s decision to target under five-year-olds for the swine flu vaccine before other parts of the population.
Overall, the researchers considered the 13% figure for infections to be low compared to past pandemics.
They also found that the average length of time between one person showing symptoms and then someone else in their house becoming ill, was 2.6 days.
The researchers said: “Our estimates of age-specific susceptibility also provide useful information for guiding public health policies that target specific age groups – policies such as school closures and vaccination efforts. In particular, our results underscore the critical role children play in the unfolding pandemic.”
The World Health Organization (WHO) said earlier this week that at least 12,220 deaths from A/H1N1 flu had now been formally confirmed around the world, but the pandemic seemed to be declining.
The toll from this virus, which emerged in April, compares less severely than that from seasonal flu, which kills between 250,000 to 300,000 people globally each year.
N Engl J Med 2009;361:2619-27