COMMENTARY

Why Are We Seeing So Much Pertussis?

William T. Basco, Jr., MD, MS

Disclosures

June 08, 2016

Impact of Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccinations on Reported Pertussis Cases Among Those 11 to 18 Years of Age in an Era of Waning Pertussis Immunity: A Follow-up Analysis

Skoff TH, Martin SW
JAMA Pediatr. 2016;170:453-458

Study Summary

This study was a follow-up of a previous analysis of outcomes of children who received only the acellular and not the whole-cell pertussis vaccine, both initially and during tetanus, diphtheria, and acellular pertussis (Tdap) booster vaccination in adolescence, adding data up through 2014. Cases of pertussis were identified by a US national surveillance system from 1990 through 2014. The children were stratified by age: less than 1 year, 1-10 years, 11-18 years, and 19 years and older. Important time points in the analysis were 2004-2005, when Tdap was introduced, and 2010, when all children would have received only the acellular pertussis vaccine through their early childhood immunizations.

More than 350,000 cases of pertussis were reported from 1990 through 2014. In the pre-Tdap era, the incidence of pertussis was already gradually increasing from 1.7 to 4.0 cases per 100,000 population. Throughout this period, infants were the age stratum most burdened by pertussis; but even in that group, the incidence markedly increased from 26.4 cases in 1991 to 127.2 cases in 2012 (per 100,000 population). The other age groups showed little change in incidence over the time period studied except for the 1- to 10-year age group, who experienced a marked increase in pertussis between 2007 and 2011. That same cohort demonstrated a significant rise in pertussis incidence when they reached age 11-18 years.

With the introduction of Tdap in 2005, pertussis cases declined at a very rapid pace among adolescents compared with all other age groups. However, in 2010, a marked increase in the incidence of pertussis occurred among 11- to 18-year-olds when those who had received only acellular vaccine throughout childhood entered adolescence. The investigators concluded that Tdap is still a very helpful vaccine for reducing pertussis in adolescence. However, the vaccine appears to be less effective overall in the cohort of adolescents who were initially immunized only with the acellular pertussis vaccine.

Viewpoint

Growing data suggest that immunity to pertussis among patients who received only acellular pertussis vaccines wanes very quickly. Waning immunity appears to be an issue for both the primary series as well as the protection conveyed by Tdap boosters. I recently reviewed a very similar study[1] that demonstrated that adolescents in the Kaiser-Permanente system who had received only acellular pertussis vaccine during the primary series had declining effectiveness of protection against pertussis after receiving Tdap. Studies have demonstrated that children who received at least one whole-cell pertussis vaccination (eg, those who were vaccinated during the period of transition between whole-cell and acellular vaccines) had better childhood protection as well as a more sustained booster effect in adolescence when they received Tdap.

Of interest, Skoff and Martin demonstrated epidemiologic peaks in pertussis incidence in 2004-2005 and 2011-2012 in virtually all age groups, including infants (age up to 12 months). This suggests that the reduced protection in adolescence explains, at least in part, the same epidemiologic spike in pertussis incidence that was noted in infants. In fact, this is such a hot topic lately that another study in the same issue of JAMA Pediatrics[2] estimated the potential benefit of a single dose of whole-cell pertussis vaccine in infancy as a way to "prime" patients for later receipt of acellular vaccine. Such a strategy would be very effective, reducing infection in neonates by 96% and perhaps saving more than $142 million in the United States annually. In any case, stay tuned because this appears to be a hot area of investigation with additional data coming every year.

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