Background incidence rates and observed-to-expected ratios of adverse events of special interest after covid-19 mRNA vaccination during pregnancy in France: a nationwide population-based study.

Background: Pregnant women are at increased risk of complications when infected by SARS-CoV-2, hence the recommendations for vaccines against COVID-19 during pregnancy. Post-marketing safety surveillance is crucial for this subpopulation typically excluded from clinical trials. Our objective was to assess the risk of adverse events of special interest (AESI) after mRNA vaccination during pregnancy using the French National Health Data System. Methods: Observed-to-expected (OE) analyses were performed on 16 AESIs and 8 negative control outcomes. Expected numbers were obtained using background incidence rates (BGIRs) from the pre-COVID-19 period (2015-2019). BGIRs were stratified by age group and pregnancy trimester (T Findings: A total of 5,267,928 pregnancies were involved in the BGIR analysis. The detailed description of BGIRs by trimester showed marked heterogeneity, with different types of trends depending on the AESI. OE ratios were assessed from 898,678 BNT vaccinations (553,236 pregnancies) and 96,415 MOD vaccinations (59,354 pregnancies). No increased risk was evidenced during pregnancy vs. the pre-conceptional period. Only two modest AESI signals, of the same order of magnitude as those of negative outcomes, were observed with MOD: Appendicitis at T Interpretation: This work did not evidence any safety signal after mRNA vaccination against COVID-19 for AESI during pregnancy. It contributes to the growing body of evidence regarding its safety. Funding: This study did not receive any specific grant.