Acellular vaccines against Bordetella pertussis protect about 75% of vaccinated children between the ages of five and nine years. Approximately 65% of these children are vaccinated for five years. However, it is not possible to eradicate the disease.
Although the vaccination rates for pertussis are also quite high in Germany, there is always a cyclical accumulation of cases of whooping cough at intervals of about 5 years. In 2017, for example, 16,834 pertussis cases were reported. It is interesting to note that around 26% of the cases reported between 2001 and 2017 were among children under 14 years of age, although vaccination rates among school-age children are 95%.
Using a mathematical model, US researchers have recently re-evaluated the protective effect of the vaccine, the duration of vaccination protection and the significance of pertussis vaccination for incidence development.
The results showed that the protective effect of the acellular pertussis vaccines decreases by about 33 so-called relative percentages per year after complete inoculation of the children. Children between the ages of 5 and 9 years enjoy at least 75% protection after such complete immunization. For about two-thirds of these children, the protective effect of the vaccination continues for a period of five years. Even if the vaccination with these numbers can by no means be regarded as perfect, certain herd immunity can also be achieved in the model.
In practice, these study results mean that no eradication of whooping cough can be achieved even with the acellular vaccines. The exact interactions of Bordetella pertussis with the immune system are still not explained in detail, which is why the vaccines are not able to protect a larger percentage of the infection. Due to the limited vaccination protection for about five years, multiple infections are possible in a person's life. Infants, young children, and older people are particularly at risk, but their immune system also generally responds less well to vaccinations.
Domenech de Cellès M et al., Duration of Immunity and Effectiveness of Diphtheria-Tetanus-Acellular Pertussis Vaccines in Children. JAMA Pediatrics 2019; http://doi:10.1001/jamapediatrics.2019.0711