Pertussis: increasing disease as a consequence of reducing transmission

Area of Science:

• Epidemiology
• Mathematical Biology
• Immunology

Background:

• Pertussis (whooping cough) cases have increased in developed countries since the 1980s, shifting to older age groups.
• This resurgence occurs despite decades of mass vaccination, with hypotheses including improved diagnostics, waning immunity, and evolving Bordetella pertussis strains.

Purpose of the Study:

• To develop and analyze a mathematical model assessing the plausibility of factors contributing to pertussis resurgence.
• To investigate the role of adaptive immunity, including temporary protection from infection and vaccination, in pertussis epidemiology.

Main Methods:

• A standard transmission model was combined with assumptions about adaptive immunity, including temporary protection and the possibility of mild infections despite immunity.
• The model explored two distinct epidemiological scenarios based on transmission intensity: low transmission with predominantly severe disease and high transmission with frequent mild infections.

Main Results:

• The model identified a reinfection threshold separating low and high transmission scenarios.
• Highest incidence of severe pertussis is predicted at intermediate transmission intensities, near the reinfection threshold.
• Pertussis resurgence may be driven by reduced transmission, independent of vaccination status or strain evolution.

Conclusions:

• Mathematical modeling suggests that a decrease in transmission intensity, rather than solely waning immunity or new strains, could be a primary driver of pertussis resurgence.
• The findings offer insights into current control measures and potential future intervention strategies for pertussis.