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Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019

Our take —

RT-PCR has limited sensitivity using nasal swab samples, even within the first 3-5 days following symptom onset (approximately 70%) and declines thereafter. 90% of patients will seroconvert within 15 days of symptom onset; average time to seroconversion was 11 days. Antibody concentrations were higher among patients with more severe disease.

Study design

Case Series

Study population and setting

173 cases of COVID-19 from the Shenzhen Third People’s Hospital (Guangdong Province, China) between January 11, 2020 and February 9, 2020. Patients had acute respiratory infection syndromes and/or abnormalities in chest computed tomography (CT) images with a detectable SARS-CoV-2 RNA in a respiratory sample for at least one time point. Critical illness (n=32) was defined as acute respiratory distress syndrome or oxygen saturation <93% who required mechanical ventilation either invasively or non-invasively.

Summary of Main Findings

Sensitivity of RT-PCR on nasal swabs is at most ~70%, 3 to 5 days post symptoms and decreases to 40% by day 9. 90% of individuals seroconvert 15 days after symptoms. The average time from symptoms to seroconversion was 11 days. Individuals with critical illness had higher concentrations of antibodies to SARS-CoV-2.

Study Strengths

Large sample size and good follow up data.

Limitations

RT-PCR was performed on nasal swabs.

Value added

Demonstrates that sensitivity of RT-PCR of nasal swabs is highly dependent on the timing of sampling.