Pertussis immunity decreases after 5 DTaP doses [Researcher Comment]

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1. Increased confirmed pertussis infection is seen 6 years after completing diphtheria, tetanus, and acellular pertussis (DTaP) vaccination.

Despite most U.S. children now receiving their full 5-dose acellular pertussis vaccination regimen, the incidence of pediatric pertussis, also known as “whooping cough,” is increasing. Researchers proposed that immunity to Bordetella pertussis, the bacterium responsible, may decrease with time despite adherence to the recommended schedule.

The current study found increases in incidence and risk ratios for pertussis illness among children who had received their full course DTaP vaccine from in the 6 years after course completion. The burden of disease was actually higher in adolescence, surprising since pertussis has classically been a disease of young children, supporting a post-vaccination loss of immunity. While the absolute disease burden may be higher than in previous years and physicians may have become more accustomed to diagnosing pertussis, the use of two very different cohorts and a strong study design provide convincing evidence of a possible waning of immunity. These findings support continued vigilance in vaccine administration and may eventually lead to a reformatting of the current DTaP vaccination schedule.

Click to read the study in Pediatrics

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1. Increased confirmed pertussis infection is seen 6 years after completing diphtheria, tetanus, and acellular pertussis (DTaP) vaccination.

Dr. Sara Yee Tartof, PhD, MPH, talks to 2 Minute Medicine: Research Fellow, Kaiser Permanente Southern California:

“In recent years, the burden of pertussis in seven- to ten-year-olds has increased – a group that had previously had a low risk of disease. We suspected that duration of protection with 5 doses of DTaP may be waning earlier than expected, and had not been well described. Therefore, we evaluated incidence rates and risk ratios of reported pertussis in the six years following receipt of the fifth DTaP dose, and found that the estimates steadily increased with each additional year post-vaccination – strongly suggesting waning of vaccine-induced immunity. However, vaccination is still the best protection we have against pertussis and maintaining strong DTaP and Tdap immunization programs is critical to control of pertussis in this period of increased circulation of disease.”

This [prospective cohort ] study included 224,378 and 179,011 children from Minnesota and Oregon, respectively, who were born between 1998-2003 and completed 5 full doses of DTaP vaccine between 4 and 6 years of age. The incidence of confirmed pertussis infection (based on Bordetella pertussis culture or polymerase chain reaction positivity) and risk ratios for developing pertussis within the 6 years following vaccination were calculated.

Researchers found significant increases in both states’ incidence rates of pertussis during follow-up, with the rate being 15.6 per 100,000 individuals at year 1 post-immunization in Minnesota, compared to 138.4 cases per 100,000 at year 6 (p < .05). In Oregon, the incidences were 6.2 per 100,000 at the end of year 1 and 24.4 per 100,000 at the end of year 6 (p <.05). Risk ratios went up from 1.9 to 8.9 in Minnesota and 1.3 to 4.0 in Oregon from years 2 to 6.

In sum: Despite most U.S. children now receiving their full 5-dose acellular pertussis vaccination regimen, the incidence of pediatric pertussis, also known as “whooping cough,” is increasing. Researchers proposed that immunity to Bordetella pertussis, the bacterium responsible, may decrease with time despite adherence to the recommended schedule.

The current study found increases in incidence and risk ratios for pertussis illness among children who had received their full course DTaP vaccine from in the 6 years after course completion. The burden of disease was actually higher in adolescence, surprising since pertussis has classically been a disease of young children, supporting a post-vaccination loss of immunity. While the absolute disease burden may be higher than in previous years and physicians may have become more accustomed to diagnosing pertussis, the use of two very different cohorts and a strong study design provide convincing evidence of a possible waning of immunity. These findings support continued vigilance in vaccine administration and may eventually lead to a reformatting of the current DTaP vaccination schedule.

Click to read the study in Pediatrics

By Leah H. Carr and Devika Bhushan

More from this author: New recommendations on genetic testing for children released; Television watching linked with antisocial behavior in children, supporting AAP recommendations; American Academy of Pediatrics releases updated vaccination schedule; Banning smoking in public places linked to reduction in asthma-related hospital admissions; Paternal distress predicts poor early childhood mental health

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