Abstract and Introduction
Abstract
Background: Pertussis infection remains an important public health problem, particularly in infants. Despite high coverage, pertussis vaccination delays can leave infants at a vulnerable age with less protection than anticipated.
Methods: Current diphtheria–tetanus–pertussis (DTaP) vaccination timeliness for the first 3 doses in the US was estimated using National Immunization Survey data. A Markov model estimated the potential impact on outcomes and costs of a hypothetical situation of vaccination at exactly 60, 120 and 180 days, compared with current timeliness. Incidence and unit cost data came from published sources. Age-specific incidence (for month of life) of pertussis and the associated probabilities of hospitalization and death for the US, during 2000–2007, were taken from a recently published US DTaP vaccination cost-effectiveness study. The cost analysis was conducted from the healthcare system's perspective over a 1-year time horizon. A regression analysis was conducted to explore the factors associated with vaccination delay.
Results: Current DTaP vaccination was estimated to be delayed by 16, 27 and 44 days, for the first, second and third doses, respectively, relative to vaccination at exactly 60, 120 and 180 days. The model estimated that vaccination at exactly age 60, 120 and 180 days could prevent approximately 278 pertussis cases, 103 hospitalizations and 1 death in infants aged <1 year in the US, gaining approximately 38 quality-adjusted life years and saving approximately $1.03 million in healthcare costs.
Conclusions: Timely administration of infant pertussis vaccine doses could potentially reduce subsequent pertussis cases, hospitalizations, deaths and medical costs in infants aged <1 year in the US.
Introduction
Pertussis infection, also called whooping cough, is a highly contagious bacterial disease caused by Bordetella pertussis. Symptoms include uncontrollable violent coughing, particularly in infants. Pertussis vaccines are well established and recommended by the World Health Organization,[1] yet pertussis was still one of the leading causes of vaccine-preventable deaths worldwide in children aged <5 years in 2008.[2]
In the US, 48,277 cases of pertussis were reported in 2012.[3] The highest incidence of pertussis was in infants aged <1 year, who are at the greatest risk for severe disease and/or death.[3] Of the 20 pertussis deaths reported in the US in 2012, 16 (80%) were in infants aged <1 year, and 15 (75%) were in infants aged <3 months.[3]
Pertussis vaccination programs have substantially reduced pertussis incidence in industrialized countries.[1] However, a vaccination program effectiveness depends on compliance with the recommended schedule. In the US, the Advisory Committee on Immunization Practices (ACIP) recommended diphtheria– tetanus–pertussis (DTaP) schedule includes a primary series of 3 doses at age 2, 4 and 6 months (with a time window of 1 month for each dose), followed by a fourth dose at age 18 months and a later booster dose.[4] Vaccine coverage levels are high in the US, with 84.6% of children aged 19–35 months receiving >=4 doses of DTaP vaccine in 2011.[5] However, high coverage can mask substantial delays before full vaccination. In 2003, children were undervaccinated for a mean of 172 days for all vaccines during their first 24 months of life.[6] Approximately 34% were undervaccinated for <1 month, 29% for 1–6 months and 37% for >6 months.[6] In Australia, although DTaP coverage rates increased from 88% to 92% between 1998 and 2001, the vaccination delay remained unchanged and the authors concluded that measurement of timeliness should be incorporated into routine monitoring of immunization program delivery success in countries with high coverage levels.[7]
Studies in the US,[6,8] Australia,[7] Sweden[9] and the Netherlands[10] have reported delays in vaccine administration that would leave children temporarily with lower levels of protection than anticipated. Vaccination timeliness is important for several reasons. In the US, children who fell behind in their vaccinations were less likely to be fully vaccinated later on.[6] Delays may also interrupt the vaccine schedule, increasing the number of office visits the parent must make to the provider, which can adversely affect compliance.[11] Prompt vaccination decreases the risk not only to the child, which may be especially important for infections such as pertussis that are potentially severe in young infants,[7] but may also reduce the risk of disease in the wider community.[11]
The primary objective of this study was to estimate DTaP vaccination timeliness for the first 3 doses and investigate the potential impact of improved timeliness on health outcomes and costs in the US, by comparing the current situation with a hypothetical situation of delivery of the 3 primary DTaP doses at exactly 60, 120 and 180 days of age. In addition, a secondary objective was to identify which factors were associated with vaccination delay.
Pediatr Infect Dis J. 2016;35(5):542-547. © 2016 Lippincott Williams & Wilkins
