Pertussis-Specific Memory B-Cell and Humoral IgG Responses in Adolescents after a Fifth Consecutive Dose of Acellular Pertussis

In order to impede the increase in pertussis incidence in the adolescent group, a school-leaving booster dose administered at the age of 14 to 16 years will be introduced in Sweden in 2016. Preceding this introduction, an open-label, randomized, multicenter, clinical trial without a control group and with blinded analysis was performed, investigating both safety and immunogenicity. Reported here are the memory B-cell and serological responses detected in a smaller cohort (n 34) of the 230 subjects recruited to the study. All subjects had received primary vaccination consisting of three doses of diphtheria–tetanus–5-component pertus-sis (DTaP5) vaccine, at 3, 5, and 12 months of age, and a tetanus–low-dose diphtheria–5-component pertussis (Tdap5) vaccine booster at 5.5 years. In this study, the subjects were randomly assigned and received either a Tdap1 or Tdap5 booster. Of the 230 participants, 34 subjects had samples available for evaluation of IgG-producing memory B-cell responses. Both vaccine groups had significant increases in pertussis toxin-specific serum IgG levels, but only the 1-component group showed significant in-creases in pertussis toxin-specific memory B cells. The 5-component group had significant increases in filamentous hemaggluti-nin- and pertactin-specific memory B-cell and serum IgG levels; these were not seen in the 1-component group, as expected. In conclusion, this study shows that a 5th consecutive dose of an acellular pertussis vaccine induces B-cell responses in vaccinated adolescents. (This study has been registered at EudraCT under registration no. 2008-008195-13 and at ClinicalTrials.gov under registration no. NCT00870350.) Pertussis, or whooping cough, is caused by the bacterium Bor-detella pertussis. It is a highly contagious disease that affects al