Effectiveness of immunization strategy transition of pertussis vaccines: an evaluation with interrupted time series and segmented regression analysis

  Objective  To evaluate the effectiveness of pertussis immunization strategy transition from diphtheria, tetanus and whole-cell pertussis vaccine (DTwP) to diphtheria, tetanus and acellular pertussis vaccine (DTaP) in Ji'nan city of Shandong province.

  Methods  We collected data on yearly pertussis incidence in Ji'nan city from 1965 through 2016 from the Notifiable Diseases Registry Database. We used interrupted time series (ITS) and segmented regression analysis (SRA) to quantitatively assess short- and long-term effect of pertussis vaccine inoculation and the transition of vaccination schedule from DTwP to DTaP on pertussis incidence in the city.

  Results  The reported pertussis incidence decreased significantly from 164.47/100 000 before the pertussis vaccine inoculation in to 145.77/ 100 000 following the implementation of DTwP inoculation in 1978 (P = 0.017) and the average long-term effect increased by 7.32/100 000 per year between 1978 and 2001. No significant short- and long-term variations in reported pertussis incidence were observed when the implementation of DTaP vaccination as a second class vaccine in 2002 (both P > 0.05). The reported yearly pertussis incidence declined significantly by 5.97, 7.39, and 8.03 per 100 000 population in 2008, 2009, and 2010 when the fourth dose, the second/third/fourth, and all doses of DTwP vaccinations were replaced by DTaP in the year, respectively (P < 0.01 for all); but an increasing trend in the reported yearly pertussis incidence was observed after the replacements of various doses of DTwP with DTaP for the periods from 2008, 2009, and 2010 to 2016, with the average annual increases of 0.29, 0.35, 0.39 per 100 000 population.

  Conclusion  The study showed that the effectiveness of an all-DTwP vaccination schedule may be less than the effectiveness of a sequential DTwP/DTaP vaccination schedule. Short-term effectiveness of DTaP vaccination was better than that of DTwP, but the duration of DTaP-induced protection is not ideal. Effective pertussis vaccines and vaccination schedules in China need to be developed.