New research in BMC Medicine proposes that the source of a recent pertussis outbreak may not be due to vaccine efficacy or decreasing immunization, but instead from infected individuals who are vaccinated and asymptomatic.

Prior research found that giving baboons acellular pertussis vaccines prevented them from developing pertussis symptoms but did not stop transmission of the disease. 

Ben Althouse, PhD, and Sam Scarpino, PhD, from the Santa Fe Institute, designed a model to build on those findings via evaluation of waning of protective immunity from vaccination or natural infection over time, evolution of B. pertussis to escape protective immunity, and low vaccine coverage. 

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The model used data from the Centers for Disease Control and Prevention (CDC) and Public Health England (PHE) on all reported pertussis cases in the United States from 1922–2012, genomic data on B. pertussis, and a detailed epidemiological model of B. pertussis transmission.

The model revealed that acellular vaccines were likely to have contributed to (and possibly exacerbated) the recent outbreak by allowing infected but asymptomatic individuals to unknowingly spread pertussis multiple times in their lifetimes. 

The level of vaccination needed for herd immunity was over 99% due to the ability of the disease to be spread via vaccinated but infected and asymptomatic individuals.

The authors emphasize that the acellular vaccine still offers protection against pertussis and that these results support the need for widespread immunization, particularly for children and those at risk of severe disease from pertussis.


1. Althouse B, et al. BMC Med. 2015, 13:146  

This article originally appeared on MPR