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Hum Vaccin. 2011 Jan 1;7(1):56-7. Epub 2011 Jan 1.

H1N1 influenza A outbreak among young medical staff members who received single dose of non-adjuvanted split-virion 2009 H1N1 vaccine.

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Department of Nephrology, Kameda Medical Center, Kamogawa, Japan.


We experienced an H1N1 influenza A outbreak among medical staff members who had received a vaccination. To investigate the preventive effects of the H1N1 influenza vaccine on the H1N1 influenza A infection, we examined the data on the medical staff members and patients with confirmed H1N1 influenza A or influenza-like illness retrospectively. Approximately half of the young individuals under 30 years of age developed H1N1 influenza A, while the diagnosis was established in 3% of medical staff over the age of 30 and 0.9% of patients with a median age of 67. The mechanism for association between age and the risk of H1N1 infection is unclear; however, it might have been associated with an age-related increase in the prevalence of neutralizing antibody titers against the 2009 H1N1 influenza A as indicated by previous reports. This study showed that current Japanese H1N1 influenza A vaccine program using one dose of non-adjuvant split-virion 2009 H1N1 vaccine with 7.5 μg hemagglutinin had a limited preventive effect on H1N1 influenza A infection in adults under 30 years of age.

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