Evaluating pertussis vaccine effectiveness in children under 5 years of age born in France between 2013 and 2019

Although effective pertussis vaccines are available and have been incorporated into national immunization programs for infants and children, and adolescents and adults in some countries, pertussis remains endemic worldwide. Periodic outbreaks occur every 2 to 5 years. In 2013, France revised its pediatric vaccination program, transitioning from a 3 + 1 to a 2 + 1 schedule. The effects of this change have raised some concerns; however, data on the effectiveness of pediatric vaccines in France post 2013 remain limited. This matched case-control study aimed to estimate the effectiveness of vaccination against pertussis in children born in France between 2013 and 2019, using the French National Health Data System. Children were included in the study if they were alive and free of pertussis at 6 weeks of age, and if their mother-child linkage was available. Pertussis-related hospitalizations were captured using the International Classification of Diseases-10 codes (A37.0 and A37.9), and vaccine exposure status was confirmed using ATCC codes (J07CA02, J07CA06, and J07CA09). The odds ratio (OR) of exposure to vaccine against pertussis for 1, 2, and 3 effective doses was calculated using conditional logistic regression models. Vaccine effectiveness (VE) was estimated as (1-adjusted OR) × 100% in at-term infants. In total, 1,481,884 children were included in the study. When stratified by age groups, a gradient of increasing VE was observed, with highest VE (93.4%) observed among children aged 11.5 to 60 months who were fully vaccinated according to 2 + 1 schedule and lowest (24.1%) among children aged 2 to 4.5 months who received only the first dose. In sensitivity analyses, imputation of missing data on vaccinations potentially received outside the healthcare insurance setting (Protection maternelle et infantile) resulted in an approximately 6% increase in VE. Results demonstrated that adherence to the 2 + 1 schedule provided effective protection against pertussis in full term children in France.