Persistently positive SARS-CoV-2-specific IgM during 1-year follow-up

Dear Editor, Immunoglobulin M (IgM) antibodies typically appear in the early stageof infection and have a short maintenance time, so IgM is frequentlyused as a diagnostic criterion for acute or recent disease.1However,unconventional IgM‐specific responses have been described in SARS‐CoV‐2 infection, raising doubts about the use of IgM as a biomarkerfor COVID‐19 and the role of this antibody in immunity to SARS‐CoV‐2