Evaluating the Association of Clinical Characteristics With Neutralizing Antibody Levels in Patients Who Have Recovered From Mild COVID-19 in Shanghai, China

IMPORTANCE: The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) threatens global public health. The association between clinical characteristics of the virus and neutralizing antibodies (NAbs) against this virus have not been well studied. OBJECTIVE: To examine the association between clinical characteristics and levels of NAbs in patients who recovered from COVID-19. DESIGN, SETTING, AND PARTICIPANTS: In this cohort study, a total of 175 patients with mild symptoms of COVID-19 who were hospitalized from January 24 to February 26, 2020, were followed up until March 16, 2020, at Shanghai Public Health Clinical Center, Shanghai, China. EXPOSURES: SARS-CoV-2 infections were diagnosed and confirmed by reverse transcriptase–polymerase chain reaction testing of nasopharyngeal samples. MAIN OUTCOMES AND MEASURES: The primary outcome was SARS-CoV-2–specific NAb titers. Secondary outcomes included spike-binding antibodies, cross-reactivity against SARS-associated CoV, kinetics of NAb development, and clinical information, including age, sex, disease duration, length of stay, lymphocyte counts, and blood C-reactive protein level. RESULTS: Of the 175 patients with COVID-19, 93 were female (53%); the median age was 50 (interquartile range [IQR], 37-63) years. The median length of hospital stay was 16 (IQR, 13-21) days, and the median disease duration was 22 (IQR, 18-26) days. Variable levels of SARS-CoV-2–specific NAbs were observed at the time of discharge (50% inhibitory dose [ID50], 1076 [IQR, 448-2048]). There were 10 patients whose NAb titers were less than the detectable level of the assay (ID50, <40), and 2 patients who showed very high titers of NAbs, with ID50 levels of 15 989 and 21 567. NAbs were detected in patients from day 4 to 6 and reached peak levels from day 10 to 15 after disease onset. NAbs were unable to cross-react with SARS-associated CoV and NAb titers correlated with the spike-binding antibodies targeting S1 (r = 0.451; 95% CI, 0.320-0.564; P < .001), receptor binding domain (r = 0.484; 95% CI, 0.358-0.592; P < .001), and S2 regions (r = 0.346; 95% CI, 0.204-0.473; P < .001). NAb titers at the time of discharge were significantly higher in the 82 men (1417 [IQR, 541-2253]) than those in the 93 women (905 [IQR, 371-1687]) (median difference, 512; 95% CI, 82-688; P = .01) and at the time of follow-up in 56 male patients (1049 [IQR, 552-2454]) vs 61 female patients (751 [IQR, 216-1301]) (median difference, 298; 95% CI, 86-732; P = .009). Plasma NAb titers were significantly higher in 56 older (1537 [IQR, 877-2427) and 63 middle-aged (1291 [IQR, 504-2126]) patients than in 56 younger patients (459 [IQR, 225-998]) (older vs younger: median difference, 1078; 95% CI, 548-1287; P < .001; middle-aged vs younger: median difference, 832; 95% CI, 284-1013; P < .001). The NAb titers were correlated with plasma C-reactive protein levels (r = 0.508; 95% CI, 0.386-0.614; P < .001) and negatively correlated with lymphocyte counts (r = −0.427; 95% CI, −0.544 to −0.293; P < .001) at the time of admission. CONCLUSIONS AND RELEVANCE: In this cohort study, among 175 patients who recovered from mild COVID-19 in Shanghai, China, NAb titers to SARS-CoV-2 appeared to vary substantially. Further research is needed to understand the clinical implications of differing NAb titers for protection against future infection.