Natural Course of Severe Acute Respiratory Syndrome–Associated Coronavirus Immunoglobulin after Infection

Abstract
To the Editor—In Chen et al.'s recent study, severe acute respiratory syndrome (SARS)-associated coronavirus (SARSCoV) IgG was shown to be persistent for up to 60 days [ 1]. Their results suggested that production of this antibody is dependent on CD4+ cells and might play a role in protective immunity against SARS CoV. On the other hand, IgM has been found to decrease and become undetectable 11 weeks into the recovery phase [ 2]. Whether survivors of SARS can have persistent antibody and lifelong immunity against SARS CoV is unknown.