Comment in response to "Asymptomatic transmission and the resurgence of Bordetella pertussis" Tami Skoff, Centers for Disease Control and Prevention 3 August 2015 The recent paper entitled "Aymptomatic transmission and the resurgence of Bordetella pertussis" buy authors Althouse and Scarpino provides compelling empirical evidence supporting the role of asymptomatic transmission in the resurgence of pertussis in many countries. While we agree with the overall study conclusions and appreciate the findings, we offer an evaluation of U.S. national surveillance data with finer granularity, challenging the authors' statement that changes in pertussis disease burden have been synchronous across age groups in the U.S. Over the last two decades, rates of reported pertussis have been steadily increasing in the U.S. and significant shifts have occurred in the age distribution of cases. Begining with 7 year olds in the year 2008, the U.S. observed an unexpected increase in reported disease among children who were on the leading edge of the first cohorts recommended to received acellular pertussis vaccines for all five doses of their childhood DTaP (diphtheria and tetanus toxoids and acellular pertussis vaccine) series. Analyzing annual reported data in the years following this observation has revealed a continuous stair step accumulation of reported cases among 7 through 10 year olds as the acellular-primed cohorts have aged, corroborating results from recent DTaP vaccine effectiveness and duration of protection studies that have found waning of immunity in the years following receipt of the 5th DTaP dose. Rates of pertussis have remained elevated among 7-10 year olds during recent epidemic years in the U.S. as acellular-primed cohorts have aged, resulting in noticeable asynchrony in age-specific disease burden. Furthermore, beginning in 2012, rates of disease were elevated among 13 and 14 year olds, most of whom had recently received Tdap (reduced-dose acellular pertussis vaccine combined with tetanus and diphtheria toxoids), once again coinciding with the aging of the acellular-primed cohort. This trend continues in 2015 among older adolescents (15 and 16 year olds). These clear changes in risk by age strongly suggest a cohort effect, arguing for the significant contribution of waning effectiveness from acellular pertussis vaccine to the resurgence. The real cause of the pertussis resurgence is likely multifactorial. Competing interests I have no competing interests.