THURSDAY, Jan. 21 (HealthDay News) -- In the 2009 H1N1 influenza pandemic, children were much more vulnerable to infection than older people and, therefore, should be the primary target group for vaccination, according to a study published online Jan. 21 in The Lancet.
Elizabeth Miller, of the Health Protection Agency Centre for Infections in London, and colleagues assessed 1,403 serum samples taken in 2008 prior to the surge in H1N1 virus infection and 1,954 serum samples taken in 2009 after the surge. The researchers compared the proportion of samples with protective antibodies to H1N1 virus in 2008 to the proportion after the 2009 surge.
In the 2008 serum samples, the researchers found that protective antibodies increased with age, ranging from 1.8 percent in children aged 0 to 4 years to 31.3 percent in adults aged 80 years and older. In London and the West Midlands, the proportion of samples with protective antibodies increased 21.2 percent between 2008 and 2009 for children younger than 5 years of age, 42.0 percent for children 5 to 14 years, and 20.6 percent for those 15 to 24 years, while no difference was discerned in older groups.
"Around one child in every three was infected with 2009 pandemic H1N1 in the first wave of infection in regions with a high incidence, 10 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," the authors write.
Two authors received grants from Novartis, Sanofi Pasteur, Baxter and CSL Australia. Another author received travel expenses from Sanofi Pasteur.
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