Pertussis rates dropping post-vaccine use

There have been significant changes in pertussis disease rates among 11-to-18-year-olds following the introduction of the two booster tetanus-diphtheria-acellular pertussis vaccines, but it is still too early to say whether those changes are the result of vaccine introduction, according to a speaker the 43^rd National Immunization Conference, held in Dallas last week.

Tami H. Skoff, MS, of the National Center for Immunization and Respiratory Diseases at the CDC said the National Notifiable Diseases Surveillance System was showing reductions in pertussis rates among adolescents in 2004, one year before the adolescent vaccines were approved.

Between 2004 and 2007, CDC officials noted a decrease among all age groups, with the largest declines among 10-to-14- and 15-to-19-year-olds (-77.3% and -66.6% respectively). Overall, the incidence of pertussis decreased from 8.81 per 100,000 people to 3.47 per 100,000 people, which Skoff said, may indicate some early protective direct effects of the vaccine. However, overall, 35% of the recommended teens actually received Tdap during the study period.

Skoff said there was a peak of pertussis in the adolescent age group in 2004, with about 26,000 cases of pertussis reported that year. She said that high rate may have led to a natural boosting of immunity in the population. She also said that changes in testing patterns and changes in testing also could have aided pertussis rate reductions.

As far as herd immunity, Skoff said that pertussis rates in infants younger than 1 dropped from an average incidence of 52.5 per 100,000 people pre-vaccine approval, to 45.3 per 100,000, however, she noted that reduction was not statistically significant. She did note however, that it has only been three years since vaccine approval and that it may take more time to see a protective effect in infants aged younger than 1. – by Colleen Zacharyczuk

For more information:

Skoff T. #72. Presented at: National Immunization Conference. March 30-April 2, 2009; Dallas.

Decreases in vaccine-targeted pediatric infectious diseases are always welcome, as these data indicate in the adolescent age groups. Of course, what proportion of the decrease is due to implementation of adolescent pertussis vaccines is hard to evaluate. The rate of vaccine use in adolescents during the study period of 2004-2007 is certainly lower than desired, and it will be important and interesting to continue to monitor Tdap utilization and pertussis prevalence not only in adolescents, but also in the young infant population. Although Tdap is relatively new, it is hoped that as clinicians, we can do better by vaccinating more adolescents.

– Edward A. Bell, PharmD

Infectious Diseases in Children Editorial Board member