A key to victory in battle, according to Chinese general and military strategist Sun Tzu, is to know your enemy. In the current fight against whooping cough resurgence, perhaps the biggest obstacle is an incomplete understanding of its underlying causes, according to a University of Michigan population ecologist.
Though the root causes of the resurgence remain "elusive and contentious," public health officials in many countries – including the United States – have introduced whooping cough booster shots into childhood immunization schedules, Pejman Rohani and a co-author state in a paper published online Jan. 19, 2015 in Proceeding of the National Academy of Sciences.
If those booster schedules are based on a misdiagnosis of the problem, the shots are likely to be "epidemiologically ineffective and economically costly," they conclude. Rohani is a professor of ecology and evolutionary biology, a professor of complex systems, and a professor of epidemiology. The first author of the PNAS paper is Maria Riolo, former postdoctoral fellow in the lab of Professor Mercedes Pascual, and former U-M doctoral student, who is now a postdoctoral researcher at the University of Chicago.
Rohani said he strongly supports childhood vaccinations and a tightening of personal-belief exemptions that allow some parents to opt out of vaccinating their children. In the U.S., the Centers for Disease Control and Prevention recommends a series of five shots for whooping cough, also known as pertussis, for children under 7. Additional shots are recommended for older children and some adults.
Riolo and Rohani used a mathematical model to identify pertussis booster schedules that result in the greatest reduction in disease for the lowest economic cost. They looked at several potential causes of the pertussis resurgence separately, though in the real world it's likely that more than one of the mechanisms are simultaneously at play.
Their mathematical model uses a "genetic algorithm" that mimics how evolution by natural selection would operate on a population of diverse booster schedules.
They found that the most effective booster schedules varied depending on the resurgence mechanisms. They looked at four possible mechanisms: insufficient vaccine coverage, low vaccine efficacy, waning immunity and a leaky vaccine.
Read more: Michigan News press release