The recent resurgence in cases of Bordetella pertussis, or whooping cough, may be caused by vaccinated people who are infectious but do not display symptoms, according to recent study data in BMC Medicine.
“An acellular B. pertussis vaccine which blocks symptomatic disease but not asymptomatic transmission is able to account for the observed increase in B. pertussis incidence; complicates situational awareness surrounding levels of current B. pertussis transmission; and potentially biases estimates of vaccine efficacy obtained from case data,” study researchers Benjamin M. Althouse, PhD, ScM, and Samuel V. Scarpino, PhD, both of Santa Fe Institute, wrote.
The researchers analyzed the incident rate of B. pertussis in the United States and United Kingdom. They compared this data with analysis of 36 genome sequence isolates of B. pertussis, gathered between 1935 and 2005, to support evidence of asymptomatic transmission.
Results showed that the timing of age-specific infection rates were consistent with asymptomatic transmission. Asymptomatic transmission also was apparent in the observed cases because the genetic diversity of the bacterial population was too high for the rate of symptomatic infections.
“There could be millions of people out there with just a minor cough or no cough spreading this potentially fatal disease without knowing it,” Althouse said in a press release. “The public health community should act now to better assess the true burden of pertussis infection.”
The investigators said vaccinating individuals in proximity to patients too young for vaccination may be ineffective based on these findings. They suggested further research is required to determine the genetic diversity of B. pertussis and the incident rate of unvaccinated individuals.
“In light of current evidence and our results, we cannot dismiss the potential far-reaching epidemiological consequences of asymptomatic transmission of B. pertussis and an ineffective B. pertussis vaccine,” the researchers wrote. – by David Costill.