Immediate adverse events following COVID-19 immunization. A cross-sectional study of 314,664 Italian subjects.

Background And Aim: The urgency of having rapidly safe and efficient COVID-19 vaccines called for the need to shorten trial phases, reduce sample sizes, and speed-up the approval process by the regulatory Agencies. In light of this, monitoring adverse effects (AEFI) (both immediate and at medium-long term) become of great importance. Aim of this cross-sectional study was to explore the associations between several factors and risk of immediate AEFI.