B cells produce a diverse antibody repertoire by undergoing gene rearrangements. Pathogen exposure induces the clonal expansion of B cells expressing antibodies that can bind the infectious agent. To assess human B cell responses to trivalent seasonal influenza and monovalent pandemic H1N1 vaccination, we sequenced gene rearrangements encoding the immunoglobulin heavy chain, a major determinant of epitope recognition. The magnitude of B cell clonal expansions correlates with an individual’s secreted antibody response to the vaccine, and the expanded clones are enriched with those expressing influenza-specific monoclonal antibodies. Additionally, B cell responses to pandemic influenza H1N1 vaccination and infection in different people show a prominent family of convergent antibody heavy chain gene rearrangements specific to influenza antigens. These results indicate that microbes can induce specific signatures of immunoglobulin gene rearrangements and that pathogen exposure can potentially be assessed from B cell repertoires. Display omitted •Human antibody gene repertoire sequencing identifies vaccine-specific B cell clones•Quantified B cell clonal expansions correlate with serological vaccine responses•Human pandemic H1N1 2009 influenza vaccine responses show convergent antibodies Infection stimulates B cells expressing antibodies specific to the pathogen. By sequencing human antibody gene repertoires, Jackson et al. determined that influenza vaccination or infection induces B cell clonal expansions, whose magnitude correlates with individual secreted antibody responses, and that different individuals use convergent antibody rearrangements specific to influenza antigens.