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Vaccine. 2010 Apr 30;28(20):3558-62. doi: 10.1016/j.vaccine.2010.03.006. Epub 2010 Mar 20.

Cross-reactive antibody responses to the 2009 A/H1N1v influenza virus in the Italian population in the pre-pandemic period.

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National Centre for Epidemiology, Surveillance and Health Promotion, Istituto Superiore di Sanità Rome, Viale Regina Elena 299, Rome, Italy.


To assess in Italy the pre-pandemic susceptibility of the general population to the 2009 A/H1N1v influenza virus, 587 serum samples collected in 2004 were analyzed using haemagglutination-inhibition (HI), single-radial-haemolysis (SRH) and microneutralisation (MN) assays. Serum samples were stratified by age group, gender, and geographic area. Overall, using HI assay, the proportion of subjects showing antibodies cross-reacting with 2009 A/H1N1v virus at seroprotection level (>or=1:40) was estimated to be 6.7%, 12.4%, and 22.4% in individuals born between 2004 and 1949, 1948 and 1939, 1938 and 1909, respectively. With a HI antibody titre of >or=1:10, in the same birth cohort, the seroprotection levels were 13.5%, 19.2%, and 58.2%, respectively. The results suggest that the Italian population was not fully naïf to the current pandemic virus and that the possible previous exposure and immune response increases with age.

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