# Adverse events following SARS-CoV-2 mRNA vaccination in norwegian adolescents

## TL;DR

This study examines adverse events in Norwegian adolescents after SARS-CoV-2 mRNA vaccination, finding rare occurrences with no significant increase after the first dose.

## Contribution

The study provides nationwide data on AEFI in adolescents, identifying specific events post-second dose.

## Key findings

- Most AEFIs were rare with few cases reported.
- No significant increase in AEFIs after first-dose vaccination.
- Increased IRRs observed for anaphylactic reaction, lymphadenopathy, appendicitis, and myocarditis after second dose.

## Abstract

The Norwegian COVID-19 vaccination campaign of adolescents from April 2021 necessitated surveillance of potential adverse events following immunization (AEFI). In this nationwide study of 496,432 adolescents, AEFI incidence rate ratios (IRRs) after first- and second-dose SARS-CoV-2 mRNA vaccination were compared to IRRs in unvaccinated subjects, and a self-controlled case series analysis was done as a secondary analysis. Seventeen pre-selected potential AEFIs were investigated: Anaphylactic reaction, Acute appendicitis, Lymphadenopathy, Arrhythmia, Cerebrovascular events, Death, Encephalomyelitis and meningitis, Epilepsy and convulsions, Facial nerve palsy, Herpes zoster, Idiopathic thrombocytopenic purpura, Myocarditis and pericarditis, Venous thromboembolic events, Arthropathy, Guillain-Barré syndrome, IgA vasculitis, and Multisystem inflammatory syndrome in children. Most AEFI were rare among adolescents, with few cases, and there was no statistically significant increase in the incidence of AEFIs after first-dose vaccination. Increased IRRs of anaphylactic reaction, lymphadenopathy, appendicitis, and myocarditis and pericarditis were observed following second-dose vaccination.

The online version contains supplementary material available at 10.1038/s41598-026-45261-2.