With the switch from the whole-cell to the acellular pertussis vaccine, rates of pertussis disease have been climbing. Worse, every year approximately 20 to 25 children die from pertussis. Virtually all of these children are less than 2 months of age, too young to benefit from active immunity. Up to this point, it has been assumed that the most likely source of pertussis transmission to infants is from the mother. For this reason, the Centers for Disease Control and Prevention (CDC) recommends that pregnant women receive a Tdap vaccine with each pregnancy. A recent study took another look at the source of transmission.
In Oct. 2015, Skoff and colleagues from the CDC, in collaboration with epidemiologists from several state public health programs, examined the source of pertussis infections (Skoff TH, Kenyon C, Cocoros N, et al. Sources of infant pertussis infections in the United States. Pediatrics. 2015 Sept 7. pii: peds.2015-1120.). Investigators focused on infant cases, meaning those children who were less than 1 year of age when they were infected; 1,306 cases were identified between 2006 and 2013. A source of infection was found in 569 cases. Infants less than 1 month of age were more likely to have a source of infection identified than those who were 2 months of age or older. The most common source of infection was siblings (35.5%), followed by mothers (20.6%) and fathers (10.0%).
These data support the notion that the most common source of infection for infants is their brothers and sisters, not their mothers. The practical interpretation of these data is that if we are going to protect infants too young to benefit from an active vaccine (i.e., those less than 2 months of age), we will need to vaccinate pregnant mothers and also make sure that all siblings in the home are up to date on their pertussis immunizations. If not, those most vulnerable will be left exposed to a potentially fatal infection.