The human respiratory tract is colonized by microorganisms which constitute the respiratory microbiota. This microbiota is involved in the protection of the host against microbial infections. Its dynamics is regulated by mechanisms such as respiratory air flows, contributing to the inhalation of microorganisms, which is balanced by the host's immune system. An imbalance of these microbial communities, called dysbiosis, seems to be involved in the occurrence of respiratory pathologies such as asthma. This pathology affects about 25% of infants and its pathophysiology suggests a microbiota damage, associated with an inflammation. Major aims of this project are to characterize the global composition of the respiratory microbiome of infants with severe asthma, to follow its evolution over time and to determine the inflammatory profile of these patients. The cohort will include 100 patients from University Hospitals of Rouen and Caen. Nasopharyngeal and bronchoalveolar samples from these patients will be sequenced by metatranscriptomic approach and will allow to describe the respiratory microbiome composition. Inflammatory markers will also be analyzed through flow cytometry and ELISA to identify links between inflammation profiles involved in severe asthma and microbiome composition.