COVID-19 induces a reliable immune response after 15 days as measured by antibody levels in blood

As serological assays begin to identify people with presumed immunity to #COVID19 #SARSCoV2—the first who will restore our societies—understanding antibody response timing is critical. This study of 173 patients suggests ~15 days to robust IgM/IgG levels David R. Liu@davidrliu on Twitter

Pre-print here (pdf)
Results Among 173 patients, the seroconversion rate for Ab, IgM and IgG was 93.1% (161/173), 82.7% (143/173) and 64.7% (112/173), respectively. Twelve patients who had not seroconverted were those only blood samples at the early stage of illness were collected. The seroconversion sequentially appeared for Ab, IgM and then IgG, with a median time of 11, 12 and 14 days, respectively. The presence of antibodies was < 40% among patients in the first 7 days of illness, and then rapidly increased to 100.0%, 94.3% and 79.8% for Ab, IgM and IgG respectively since day 15 after onset. In contrast, the positive rate of RNA decreased from 66.7% (58/87) in samples collected before day 7 to 45.5% (25/55) during days 15 to 39. Combining RNA and antibody detections significantly improved the sensitivity of pathogenic diagnosis for COVID-19 patients (p < 0.001), even in early phase of 1-week since onset (p = 0.007). Moreover, a higher titer of Ab was independently associated with a worse clinical classification (p = 0.006). Conclusions The antibody detection offers vital clinical information during the course of SARS-CoV2 infection. The findings provide strong empirical support for the routine application of serological testing in the diagnosis and management of COVID-19 patients.

Prof. Zheng Zhang, PhD, MD. Institute of Hepatology, Shenzhen 3rd People’s Hospital, Shenzhen 518112, Guangdong Province, China
Email: zhangzheng1975@aliyun.com. Prof. Lei Liu, MD, Shenzhen 3rd People’s Hospital, Shenzhen 518112, Guangdong Province, China; Email: liulei3322@aliyun.com. Prof. Sheng-Xiang Ge, PhD, The State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, National Institute of Diagnostics and Vaccine Development in Infectious Diseases, Xiamen University, Xiamen 361102, China; Phone: 86-0592-2184110; Fax: 86-0592-2181258; Email: sxge@xmu.edu.cn. Prof. Jun Zhang, MSc, The State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, National Institute of Diagnostics and Vaccine Development in Infectious Diseases, Xiamen University, Xiamen 361102, China; Phone: 86-0592-2184110; Fax: 86- 0592-2181258; Email: zhangj@xmu.edu.cn.

See also

• How blood from coronavirus survivors might save lives
• New York City researchers hope antibody-rich plasma can keep people out of intensive care.