There is a lack of understanding as to why some people suffer from long-lasting symptoms after COVID-19 infection. A new study from Karolinska Institutet in Sweden, and the Helmholtz Center Munich (HMGU) and the Technical University of Munich (TUM), both in Germany, now demonstrates that a certain type of immune cells called macrophages show altered inflammatory and metabolic expression several months after mild COVID-19. The findings are published in the journal Mucosal Immunology.