A shift from mothers to siblings as the most common source of pertussis transmission to infants was identified in a study of 1,306 infant cases with source of infection (SOI) being identified as a suspected pertussis case in contact with the infant case 7 to 20 days before infant cough onset. Researchers determined:

• >66% of SOIs were immediate family members, most commonly siblings (35.5%), mothers (20.6%), and fathers (10%).

• Mothers predominated until the transition to siblings beginning in 2008 (8-year analysis).

• Overall SOI median age was 14 years; median age for sibling SOI was 8 years.

• Prevention efforts should focus on increasing Tdap coverage during pregnancy.

Citation: Skoff TH, Kenyon C, Cocoros N, et al. Sources of infant pertussis infection in the United States. Pediatrics. [Published online ahead of print September 7, 2015]. doi:10.1542/peds.2015-1120.

Commentary: Immunizations are critical. The current study reminds us of the importance of family members as sources of exposure for infants and the importance of correct immunization of family members. The recommendations for pertussis vaccination in pregnancy have changed substantially in the last few years. Based on evidence that transplacetal transfer of mothers’ antipertussis antibodies to the fetus protects infants until their 2-month pertussis vaccinations, and that immunity wanes after about 2 years, the ACIP recommends that, in pregnant women, Tdap should be administered during the third trimester of every pregnancy, regardless of the patient's prior history of receiving Tdap, ideally between 27 and 36 weeks of gestation¹. As for siblings, ACIP recommends completing the childhood series. Acellular pertussis vaccine is recommended at 4-5 years of age, and a booster is recommended at 11-12 years of age. —Neil Skolnik, MD

1. Sawyer M, Liang JL, Messonnier N, Clark TA. Updated recommendations for use of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine (Tdap) in pregnant women – Advisory Committee on Immunization Practices (ACIP), 2012. MMWR 2013;62:131–135.