LAUSR

Cross-protection from previous live attenuated vaccines is proposed to explain the low impact of COVID-19 on children. This study aimed to evaluate the effect of live attenuated MMR vaccines on the risk of being hospitalized for COVID-19 in children. An exposed (MMR vaccine)–non-exposed cohort study was conducted using the nationwide French National Health Data System (SNDS). We included children born between 1 January 2009 and 31 December 2019. Exposure was defined as a claim of at least one dose of MMR vaccine since birth. Hospitalization for COVID-19 was defined using main diagnostic ICD10 codes. Non-conditional logistic regression was used to calculate the adjusted odds ratios (aORs) of the association between MMR exposure and hospitalization for COVID-19, controlling for socio-demographic and socio-economic factors, co-morbidities, and general health. In total, 6,800,542 (median age 6 IQR [3–8] years) children exposed to a MMR vaccine and 384,162 (6 [3–9] years) not exposed were followed up with for 18 months. Among them, 873 exposed to the MMR vaccine and 38 who were not exposed were hospitalized for COVID-19. In a multi-variate analysis, the exposure of children to MMR vaccination was not associated with a decreased risk of COVID-19 hospitalization versus non-exposure (aOR (95%CI) = 1.09 [0.81–1.48]). A stratified analysis by age showed an aOR = 1.03 [0.64–1.66] for children aged 1–4, an aOR = 1.38 [0.82–2.31] for those aged 5–9, and an aOR = 1.11 [0.54–2.29] for those aged 10–12. Our study suggests that the live attenuated MMR vaccine does not protect children against COVID-19 hospitalization.