Two-Year Prospective Study of the Humoral Immune Response of Patients with Severe Acute Respiratory Syndrome

Liu, Wei; Fontanet, Arnaud; Zhang, Pan-He; Zhan, Lin; Xin, Zhong-Tao; Baril, Laurence; Tang, Fang; Lv, Hui; Cao, Wu-Chun

In a cohort study of 56 convalescent patients with severe acute respiratory syndrome (SARS), titers of immunoglobulin G (IgG) antibodies and neutralizing antibodies (NAbs) against SARS-associated coronavirus were assessed at regular intervals (at 1, 4, 7, 10, 16, and 24 months after the onset of disease) by use of enzyme-linked immunosorbent assay and neutralization assay. IgG antibody and NAb titers were highly correlated, peaking at month 4 after the onset of disease and decreasing thereafter. IgG antibodies remained detectable in all patients until month 16, and they became undetectable in 11.8% of patients at month 24. The finding that NAbs remained detectable throughout follow-up is reassuring in terms of protection provided against reinfection; however, NAb titers decreased markedly after month 16