Influenza -Like Illness

Title: Mucosal and systemic immunity correlates of protection against influenza in young children (MUSIC-Flu). The goal of this observational study is to better understand how immune responses in the blood and mucosa are linked to protection against influenza infection and illness in young children. We will compare immune responses in children who get influenza infection to those who do not. Children aged 2-5 years of age will be followed from April through October 2026 during the influenza season in South Africa. During this time, nasal swabs will be collected three times per week to test for influenza and other respiratory viruses. Information on symptoms and temperature will be collected by nurses at weekly visits and daily by caregivers using an electronic symptom diary. Blood samples will be collected before and after the influenza season, and at two additional time points during the study. Special immune cells will also be collected from blood samples before and after the season. In addition, samples from the nose and mouth will be collected every month. These samples will be tested to measure immune responses, including antibodies, signaling proteins (cytokines), and specific immune cells (T cells and B cells).

Every year in the fall and winter, numerous respiratory viruses (such as influenza viruses, SARS-CoV-2 (COVID-19), RSV, rhinovirus, and metapneumovirus) circulate in mainland France, causing acute respiratory infections (ARIs). These viruses can cause epidemics of varying severity, requiring close monitoring to determine their circulation levels and adapt public health measures accordingly. In France, ARI surveillance relies on two networks: the Sentinelles network in primary care and the RENAL network in hospitals. The Sentinelles surveillance is conducted in collaboration with Santé publique France, the National Reference Center for Respiratory Infection Viruses (Institut Pasteur and Hospices Civils de Lyon), and the University of Corsica. As part of the virological surveillance of ARIs, Sentinelles physicians are asked to collect nasopharyngeal swabs or saliva samples from a sample of patients presenting with an ARI during their clinic visits. This surveillance makes it possible to identify respiratory viruses circulating in primary care (general practice and pediatrics), to describe confirmed cases for each of the circulating viruses, and to estimate the impact of each on general practice. This surveillance also allows for the evaluation of the effectiveness of vaccines against influenza and COVID-19.