Pertussis is a highly contagious disease whose complications can be very serious, particularly in infants who have not been vaccinated or have not completed their vaccination series. Various studies have shown that, in the majority of cases, parents or siblings are the primary sources of infection for young children. In 2004, in addition to the standard pertussis vaccination schedule, the French High Council for Public Health recommended vaccinating couples planning to have children or, failing that, updating the vaccinations of all household members during pregnancy and as soon as possible after childbirth for the mother. This strategy, known as "cocooning," was supplemented in 2008 by the recommendation to administer a pertussis booster during the 10-year dTP booster for 26- to 28-year-olds to all adults who had not received a pertussis vaccination in the past 10 years. The objective of this study, which examined reimbursement data for individuals aged 20 to 39 enrolled in the general health insurance scheme in 2007 and 2008 in the Île-de-France region, was to conduct an initial assessment of the number of pertussis vaccines prescribed and reimbursed in the Île-de-France region, as well as the characteristics of the recipients and prescribers of this vaccine. Despite the limited number of years studied, the results revealed a widespread increase in dTcaP prescriptions at the expense of dTP between 2007 and 2008, across all age groups and all departments in the Île-de-France region. These prescriptions are primarily issued by general practitioners, but less than 2% are issued by pediatricians or gynecologists, despite their central role in the "cocooning" strategy. This analysis will be repeated regularly in the coming years to assess the impact of the regional program aimed at raising awareness among healthcare professionals regarding the prescription of the pertussis vaccine for young adults in the Île-de-France region. (R.A.)