Serological follow-up of SARS-CoV-2 asymptomatic subjects

TLDR

SARS‑CoV‑2 symptoms are non‑specific, ranging from asymptomatic to severe pneumonia, and asymptomatic carriers often remain undiagnosed, raising uncertainty about antibody development and persistence. This study aimed to assess the emergence and durability of SARS‑CoV‑2 antibodies in asymptomatic individuals. The authors followed 31 asymptomatic participants from the UNICORN cohort who had a positive nasal swab or Spike‑RBD Ig in March 2020, collecting a second blood sample eight weeks later for IgM, IgG, total antibodies and a structured questionnaire. Results showed that about 80 % of asymptomatic subjects lacked circulating antibodies after eight weeks, more than 40 % never had detectable Ig, and two‑thirds of those with baseline Ig lost IgG by week 8, indicating that most asymptomatic infections do not elicit lasting RBD‑Spike antibodies and affecting serological interpretation.

Abstract

Abstract SARS-CoV-2 symptoms are non-specific and can range from asymptomatic presentation to severe pneumonia. Asymptomatic subjects carrying SARS-CoV-2 often remain undiagnosed and it is still debated whether they develop immunoglobulins (Ig) and how long they persist. The aim of this study was to investigate the development and persistence of antibodies against SARS-CoV-2 in asymptomatic subjects infected by the virus. This follow-up study was performed on the 31 asymptomatic subjects who presented a positive nasal swab or serology against SARS-CoV-2 (Ig against Spike-RBD) in the first part of the UNICORN study (March 2020) aimed at attesting previous or current contacts with the virus in the personnel of the University of Milan. Eight weeks after the first Ig measure, these subjects were invited to donate a second blood sample for testing serum antibodies (IgM, IgG and total antibodies) and to fill-in a structured questionnaire. About 80% of asymptomatic subjects did not present circulating immunoglobulins against SARS-CoV-2 after 8 weeks from a positive nasal swab against the virus. Moreover, in more than 40% of these subjects, no Ig against SARS-CoV-2 were detected at any time. Finally, about two third of subjects with immunoglobulins at baseline did not present IgG against SARS-CoV-2 after 8 weeks. The majority of subjects who developed an asymptomatic SARS-CoV-2 infection do not present antibodies against the RBD-spike protein after 8 weeks of follow-up. These data should be taken into account for the interpretation of the serological evidences on SARS-CoV-2 that are emerging nowadays.