Tami H. Skoff
The overall incidence of pertussis in the United States increased between 2000 and 2016, with age-specific case counts coinciding with the transition to acellular vaccination, according to study results published in Clinical Infectious Diseases.
“The introduction of childhood pertussis vaccines dramatically altered the epidemiologic landscape of pertussis, with reported cases declining to a nadir of just over 1,000 (0.47/100,00 population) by the mid-1970s,” Tami H. Skoff, MS, epidemiologist in the CDC’s National Center for Immunization and Respiratory Diseases, and colleagues wrote. “However, despite substantial declines in disease since the prevaccine era, pertussis remains a significant health problem worldwide, with incidence increasing in several countries in recent years.”
Skoff and colleagues noted that pertussis vaccines are administered throughout a patient’s life to protect against pertussis, with a five-dose series recommended for children aged 2 months to 6 years. Whole-cell vaccine formulations were originally used in the U.S., but safety concerns prompted the transition to acellular vaccines between 1992 and 1997, they said. According to the study, DTaP coverage has remained relatively stable since the vaccine was introduced, with 93.7% of children aged 19 to 35 months receiving at least three doses in 2016.
Skoff and colleagues used the National Notifiable Diseases Surveillance System to identify pertussis cases reported between 2000 and 2016. They compared differences in characteristics and calculated average annual incidences overall, by age and by geographic subgroup.
According to the study, 339,420 pertussis cases were reported between 2000 and 2016. White (88.2%) and non-Hispanic (81.3%) people comprised the majority of patients, with 9.9% of cases resulting in hospitalization and 0.12% cases being fatal.
Differences in cases occurred by age. Infants aged younger than 1 year had the highest average annual pertussis incidence (75.3/100,000), which exceeded the incidence in other age groups by a range of 4.1 to 62.8 times, Skoff and colleagues reported. There were comparable incidences among children aged 1 to 6 years, 7 to 10 years, and 11 to 18 years, with a range from 13.8/100,000 among children aged 1 to 6 years to 18.3/100,000 among children aged 7 to 10 years. Infants accounted for 88.8% of all deaths, the researchers wrote.
There was a significant increase in the incidence of pertussis over time (P = .0019), with a 1.7-fold rise in baseline rates between 2000-2008 and 2009-2016. Patients aged younger than 1 year and 19 to 64 years did not experience significant increases during that time.
According to Skoff and colleagues, elevated case counts among patients aged 7 to 10 years and 11 to 18 years “coincided with the aging of acellular-primed birth cohorts.”
“Despite the accomplishment of the U.S. immunization program, pertussis remains endemic, and reported cases have been increasing,” they wrote. “This analysis of 17 years of national surveillance data highlights this gradual but steady increase in cases. Furthermore, as these data have shown, baseline pertussis incidence has increased nearly two-fold when comparing the later to earlier part of our study period, with incidents in peak years increasing in magnitude.”
“While emerging data suggest the causes are likely multifactorial,” they continued, “numerous studies have highlighted the key role that waning acellular vaccine immunity plays in the United States and other countries that have transitioned away from whole-cell vaccination programs.” – by Bruce Thiel
Disclosures: The researchers report no relevant financial disclosures.