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Efficacy of pertussis booster vaccination varied by resurgence method
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Efficacy of booster vaccination schedules for pertussis was contingent on how the disease resurged, according to new study findings.
“Despite the discussion surrounding the efficacy and epidemiological effectiveness of pertussis vaccines, several countries experiencing increased pertussis incidence have supplemented their existing routine infant immunization schedule with additional booster doses,” study researchers Maria A. Riolo, PhD, of the University of Chicago, and Pejman Rohani, PhD, of the University of Michigan, wrote. “Importantly, the timing and number of recommended booster doses vary considerably between countries.”
Pejman Rohani
Using a stochastic, age-stratified transmission model within a genetic algorithm framework, researchers investigated how to best and most cost-effectively mitigate pertussis via booster vaccination. They examined four scenarios: insufficient vaccine coverage, low efficacy, waning vaccine immunity and leaky immunity.
The insufficient vaccine coverage scenario simulated an efficacious vaccine with 70% uptake. In the low-efficacy scenario, simulations assumed 100% eventual vaccine uptake and a 30% probability of uptake failure. The waning vaccine immunity scenario assumed 100% uptake of a fully effective vaccine with a mean duration of vaccine-derived immunity of 15 years. The leaky immunity scenario assumed a vaccinated patient had a 14.5% chance of infection after exposure.
“In reality, it is likely that more than one of these mechanisms may be simultaneously at play in a given population,” the investigators wrote. “However, in order to disentangle the control impacts of each factor systematically, we make the pragmatic assumption that in each scenario, only the focal mechanism is responsible for ongoing chains of pertussis transmission.”
The genetic algorithm indicated that when pertussis burden was due to low vaccination coverage, the optimal booster strategy involved minimal vaccination among older age groups and focused most on targeting young children. This strategy achieved greater disease reduction with lower vaccination effort compared with other strategies.
Similarly, optimal strategies for the insufficient coverage scenario involved introduction of a single booster dose at ages 1, 2, 3, 4, or 5 years.
In the waning vaccine immunity scenario, the most successful immunization schedules included three booster doses among patients aged 6 to 19 years, administered every 5 years, followed by additional boosters when aged between 25 and 45 years.
The genetic algorithm found no booster schedules that effectively reduced disease burden in the leaky immunity scenario.
“Our results reinforce the importance of ongoing efforts to better understand vaccine-derived pertussis immunity since it is central to developing cost-effective control strategies,” Riolo and Rohani wrote. “If the cause of resurgence is vaccine leakiness, then no worthwhile booster strategies are able to combat this problem, pointing toward the need for new vaccines.”
Disclosure: The study was funded by the NIH. The researchers report no relevant financial disclosures.
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Riolo MA. Proc Natl Acad Sci USA. 2015; [published ahead of print Jan. 19].
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