Children at Greater Risk for H1N1

Study confirms that children, not the elderly, are most at risk to catch H1N1

ByABC News
December 31, 2009, 11:49 AM

Dec. 31, 2009— -- A study of household transmission of the H1N1 pandemic flu has confirmed that children 18 and younger are more at risk than young adults and seniors.

Compared with adults ages 19 through 50, children in households where someone had confirmed H1N1 flu were twice as likely to become infected, according to Simon Cauchemez, of Imperial College London and colleagues there and at the CDC.

Adults older than 50, on the other hand, were less likely to come down with the disease, Cauchemez and colleagues reported in the Dec. 31 issue of the New England Journal of Medicine.

The study also showed that the transmission rate of the virus is relatively low, the researchers said.

Since the start of the pandemic in April, children have been seen to be at greater risk, Cauchemez told MedPage Today, but the observations might have been explained by a case-ascertainment bias, since children would be more likely to be tested than adults.

It might also have been the case that school clusters -- which played a role in the early phase of the outbreak -- were biasing observations, he said.

The current study, Cauchemez said, "narrows the assumptions we can make on why there are more children among cases," he said. It could be, he said, that children have weaker immunity to flu, or there might be social interactions that make them more vulnerable.

To help understand the age effects, as well as other factors involved in transmission, the researchers used data collected by the CDC on 938 households in which there was a confirmed or probable case of the H1N1 flu, the so-called index patient.

For this study, the researchers looked at a subset of 216 households in which the index patient reported having household contacts and data was complete for all 600 of them.