Fernández Prada, MaríaRivero Calle, IreneCalvache González, AnaMartinón Torres, Federico2021-08-112021-08-112021Euro Surveill. 2021; 26(10): pii=2100193. https://doi.org/10.2807/1560-7917.ES.2021.26.10.21001931560-7917http://hdl.handle.net/10347/26768Monitoring adverse reactions following immunisation is essential, particularly for new vaccines such as those against COVID-19. We describe 20 cases of acute onset of a single supraclavicular lymphadenopathy manifesting between 24 h and 9 days after ipsilateral intramuscular administration of an mRNA-based COVID-19 vaccine, referred to our WHO Collaborating Centre for Vaccine Safety. Our results indicate that the swelling of supraclavicular lymph nodes following immunisation may constitute a benign and self-limited condition, related to a higher than recommended injection siteengThis article is copyright of the authors or their affiliated institutions, 2021. This is an open-access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0) Licence. You may share and adapt the material, but must give appropriate credit to the source, provide a link to the licence and indicate if changes were madeAtribución 4.0 Internacionalhttp://creativecommons.org/licenses/by/4.0/journal article10.2807/1560-7917.ES.2021.26.10.21001931025-496Xopen access