Background: Despite high pertussis-containing vaccine coverage in the United States, children who are unvaccinated or not fully vaccinated remain susceptible to pertussis. Over multiple birth cohorts of incomplete vaccination, the number of children not immune to pertussis will accumulate because of factors such as age-specific vaccination status and dose-specific vaccine effectiveness. The total number of pertussis-susceptible children 0–23 months of age in the United States is unknown.
Methods: Using data on age-specific pertussis-containing vaccine receipt among children evaluated in the 2013 National Immunization Survey (born between February 2011 and June 2012) and accounting for vaccine effectiveness and maternal transfer of antipertussis antibodies, we estimated the cumulative number of pertussis-susceptible children 0–23 months of age.
Results: Of an estimated 7,905,672 children 0–23 months of age in the United States, we estimated that approximately 22% (1,716,429) are susceptible to pertussis. Age was a large factor in susceptibility, with 89% of children less than 2 months of age not immune to pertussis compared with 7% of children 21–23 months of age. In sensitivity analysis, increasing maternal pertussis vaccination coverage from 10% to 42% decreased susceptibility in children less than 2 months of age to 68%. When considering waning immunity after the fourth dose of vaccine, the herd protection threshold was no longer reached.
Conclusions: These estimates underscore the need to monitor age-specific pertussis vaccine coverage, to increase childhood and maternal pertussis vaccine coverage, to maintain population-level immunity and to prevent the spread of pertussis among young children.
From the *Department of Epidemiology, Rollins School of Public Health, Emory University, †Hubert Department of Global Health, Rollins School of Public Health, Emory University, and ‡Emory Vaccine Center, Atlanta, Georgia.
Accepted for publication December 12, 2016.
The National Immunization Survey 2013 is available from the Centers for Disease Control and Prevention [US Department of Health and Human Services (DHHS). National Center for Health Statistics. The 2014 National Immunization Survey. Hyattsville, MD: Centers for Disease Control and Prevention, 2014. http://www.cdc.gov/nchs/nis/data_files.htm]. All analyses, interpretations or conclusions reached are attributable to the authors and not to the National Center for Health Statistics (NCHS), which is responsible only for the initial data.
The authors have no funding or conflicts of interest to disclose.
Address for correspondence: Robert A. Bednarczyk, PhD, CNR 7019, Hubert Department of Global Health, Rollins School of Public Health, Emory University, 1518 Clifton Rd NE, 30322 Atlanta, GA. E-mail: firstname.lastname@example.org.