(172) Impact of Live Attenuated Measles, Mumps and Rubella (MMR) Vaccines on The Risk of Hospitalization with COVID-19 in Children: A Cohort Study of 7 million Children in France

Publication Number: 1217

Background: From the beginning of Covid-19 pandemic in 2020, children have always been the least affected population compared with adults. A cross-protection of previous live attenuated vaccinations has been put forward to explain Covid’s low impact in children; but the litterature is controversial on this topic.

Objectives: To evaluate the effect of live attenuated MMR vaccine on the risk of being hospitalized with Covid-19 in children.

Methods: We conducted an exposed/non-exposed cohort study using the nationwide French health care database (SNDS), which records all in-and outpatient claims, as well as hospital discharges, for more than 65 million inhabitants from birth to death. We included all children born between January 1, 2009 and December 31, 2019 and followed them from March 1, 2020 to August 31, 2021. Exposure was defined as a claim for at least one dose of MMR vaccine (ATC code J07BD52) ever since birth. Study outcome consisted of Covid-19 main, related or associated hospitalization diagnosis (ICD10 codes). Variables significantly associated with both exposure and hospitalization for Covid-19 were selected for multivariate analysis. We used a conditional logistic regression to evaluate the association between MMR exposure and hospitalization with Covid-19, controlling for age, sex, universal health coverage, residence, social deprivation index and paediatric chronic conditions.

Results: The children’s cohort included 7,184,704 (49% female) followed during 18 months, among which data on MMR exposure was available on 6,800,542 (median age 6 years IQR [3-8]) and 384,162 (6 years [3-9]) exposed and non-exposed respectively. Among them, 1,747 and 83 were hospitalized in exposed and non-exposed groups respectively. Exposure to MMR vaccine in children was not associated with a decreased risk of Covid hospitalisation compared to non-exposure (Adjusted Odd Ratio aOR [95%CI] =0.94 [0.78-1.15]). Exploration of factors of Covid-19 hospitalization identified significant aOR for Universal Health Coverage (1.79 [1.61-1.98]), respiratory diseases (2.35 [2.09-2.64]), neurologic diseases (4.06 [3.34-4.94]), congenital or genetic defects (2.72 [2.01-3.68]), and metabolic diseases (2.94 [2.10-4.12]).

Conclusions: Our study suggests that the live attenuated MMR vaccine does not protect children against Covid-19 hospitalization. However our study could not take into account children with a prior positive PCR test; Additional studies are needed to confirm our results.