An increase in pertussis incidence has led researchers to question the durability of acellular pertussis vaccines. Though considered safer than the whole cell pertussis vaccine, a new study published in the journal Pediatrics suggests that patients vaccinated with acellular pertussis vaccine may need earlier booster vaccination and repeated boosting in order to achieve “herd effects” to curtail pertussis spread.
Researchers reviewed 11 articles published before October 10, 2013 in their analysis to see what the probability of vaccine failure was based on the odds of pertussis diagnosis and the time since the last dose of diphtheria-tetanus-acellular pertussis (DTaP); all of the studies included data on long-term immunity after 3 or 5 doses of DTaP.
No significant difference was seen between the 3- vs. 5-dose regimens with regards to annual odds of pertussis, but there was a greater absolute risk in the studies examining the 5-dose regimen which included older age groups. This finding may explain the recent increase in incidence of pertussis in older children in the U.S. and Canada. The data also suggest that for every year after the last dose of DTaP, the odds of pertussis increase by 1.33 times. Assuming 85% vaccine efficacy, the authors estimate that 10% of patients vaccinated with DTaP would be protected from pertussis 8.5 years after the last dose.
The results of this study, which the authors say is the first to examine the duration of protective pertussis immunity after routine childhood vaccination with DTaP, brings to light the importance of boosting strategies for adolescents to ensure that pertussis protection is maintained. In the U.S., Tdap booster for adolescents is recommended between the ages of 10 and 12 years, which based on the results of the study, seems to be an appropriate time. In addition, while the incidence of pertussis infection is generally lower in adults, if waning immunity to Tdap (the adolescent/adult formulation which contains lower concentrations of antigens for pertussis) is similar to that of DTap, then repeated boosters would be necessary in the adult population to maintain high levels of pertussis protection.
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