Determining the Best Strategies for Maternally Targeted Pertussis Vaccination Using an Individual-Based Model.

Rising pertussis incidence has prompted a number of countries to implement maternally targeted vaccination strategies to protect vulnerable infants, but questions remain about the optimal design of such strategies. We simulated pertussis transmission within an individual-based model parameterized to match Australian conditions, explicitly linking infants and their mothers to estimate the effectiveness of alternative maternally targeted vaccination strategies (antenatal delivery vs. postnatal delivery) and the benefit of revaccination over the course of multiple pregnancies. For firstborn infants aged less than 2 months, antenatal immunization reduced annual pertussis incidence by 60%, from 780 per 100,000 firstborn children under age 2 months (interquartile range (IQR), 682-862) to 315 per 100,000 (IQR, 260-370), while postnatal vaccination produced a minimal reduction, with an incidence of 728 per 100,000 (IQR, 628-789). Subsequent infants obtained limited protection from a single antenatal dose, but revaccinating mothers during every pregnancy decreased incidence for these infants by 58%, from 1,878 per 100,000 subsequent children under age 2 months (IQR, 1,712-2,076) to 791 per 100,000 (IQR, 683-915). Subsequent infants also benefited from household-level herd immunity when antenatal vaccination for every pregnancy was combined with a toddler booster dose at age 18 months; incidence was reduced to 626 per 100,000 (IQR, 548-691). Our approach provides useful information to aid consideration of alternative maternally targeted vaccination strategies and can inform development of outcome measures for program evaluation.