Pertussis epidemic despite high levels of vaccination coverage with acellular pertussis vaccine

We describe the pertussis epidemic, based only on confirmed whooping cough cases. We have analyzed data on the diagnosis, epidemiology and vaccine history in order to understand the factors that might explain the trends of the disease.

A descriptive study of the confirmed pertussis cases reported during 2011 in the Vallès region (population 1,283,000). Laboratory criteria for confirmed pertussis cases include isolation of Bordetella pertussis from a clinical specimen or detection of B. pertussis by PCR in nasopharyngeal swabs.

A total of 421 pertussis confirmed cases were reported, which was the highest incidence reported in the last decade (33 cases/100,000 people/year in 2011). The highest incidence rate was among infants less than 1 year old (448/100,000), followed by children 5-9 years old (154/100,000). Pertussis cases aged 2 months-1 year were 90% vaccinated following the current DTaP schedule for their age group in Catalonia, and cases of 5-9 years were 87% fully vaccinated with 5 doses of DTaP vaccine. There were no deaths, although 8% of cases were hospitalized. Pertussis was more severe in infants, 30% required hospitalization despite having received the vaccine doses corresponding to their age. Children of 5-9 years were most often identified as primary cases in households or school clusters.

Despite high levels of vaccination coverage, pertussis circulation cannot be controlled at all. The results question the efficacy of the present immunization programmes.