Influenza-specific plasmablasts are persistently induced throughout infection, providing a rich source of antiviral mAbs B cell responses were examined in nine patients infected with the pandemic 2009 H1N1 influenza virus. These patients had varying courses and severity of disease. The cases ranged from mild disease with rapid viral clearance within a few days after onset of symptoms to severe cases that shed virus for several weeks and required hospitalization with ventilator support. A majority of the patients were treated with antiviral drugs. The diagnoses were confirmed by pandemic H1N1-specific RT-PCR and serology. All patients had neutralizing titers of serum antibodies at the time of blood collection. A summary of the clinical patient data are shown in Table I . The majority of samples were obtained around 10 d after the onset of symptoms, with the exception of a particularly severe case where sampling was done 31 d after symptom onset.