Abstract
Impact of pertussis vaccines on mortality is a key World Health Organization indicator, and trends in mortality rates and age distribution can inform maternal immunization strategies. We systematically reviewed studies reporting pertussis mortality rates (PMRs) per million population, identifying 19 eligible studies. During a prevaccine observation period of ≥50 years in high-income countries (HICs), PMRs reduced in both infants and 1- to 4-year-olds by >80%, along with improvements in living conditions. In studies in low- and middle-income countries (LMICs), PMRs resembled highest prevaccine HIC rates. Postvaccine in HICs, significant further reduction in deaths (>98%) occurred, but with a large left shift in age of onset among residual deaths. Postvaccine in LMICs, limited data also show large and rapid decreases in PMRs, first in older infants and children, but long-term data fully enumerating residual deaths are lacking. In Sweden, large increases in the prevalence of undetectable pertussis antibodies were found at 10 years after high childhood coverage of acellular pertussis vaccines. Such data are not available from LMICs using whole-cell vaccines in a primary schedule without boosters. Data on residual infant deaths and maternal seroprevalence would be valuable inputs into consideration of pertussis vaccination in pregnancy in LMIC settings, especially if more precise immune correlates of infant protection against death from pertussis were known.
Highlights
The clinical syndrome of whooping cough has been recognized for at least 500 years, the causative organism, Bordetella pertussis, was not identified until 1906 [1]
As physician diagnosis of the clinical syndrome of whooping cough, in its typical form in unimmunized children, is highly specific when judged against culture as gold standard [2] and an episode of whooping cough is reliably recalled by mothers, even in resource-poor settings [3], historical data on trends in whooping cough incidence should have acceptable validity, if reporting and recording have remained consistent over time
For highincome countries (HICs), studies were from Argentina [13], Australia [14], Denmark [15, 16], Germany [17], Ireland [18], Italy [19], New Zealand [20], Switzerland [21], the United Kingdom [22,23], and the United States [24,25,26]
Summary
The clinical syndrome of whooping cough has been recognized for at least 500 years, the causative organism, Bordetella pertussis, was not identified until 1906 [1]. As physician diagnosis of the clinical syndrome of whooping cough, in its typical form in unimmunized children, is highly specific when judged against culture as gold standard [2] and an episode of whooping cough is reliably recalled by mothers, even in resource-poor settings [3], historical data on trends in whooping cough incidence should have acceptable validity, if reporting and recording have remained consistent over time. Population-based studies of severe morbidity from pertussis in resource-poor settings are sparse, especially several years after achievement of acceptable vaccine coverage through the Expanded Programme on Immunization (EPI). S134 CID 2016:63 (Suppl 4) Chow et al context, by collating estimates of pertussis mortality rates from population-level studies reporting pertussis deaths in the preand postvaccine eras
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