[Analysis of anti-SARS-CoV-2 IgG antibodies in hematologic patients with asymptomatic or mildly symptomatic COVID-19 infections]

At our institution, an outbreak of hospital-acquired coronavirus infection (COVID-19) occurred in the hematology department. We used immunochromatography to examine the anti-COVID-19 IgG antibody level in 10 COVID-19 positive patients who exhibited little or no symptoms. Six patients were negative for IgG antibody at an average of 26 days (range: 11-39 days) after the COVID-19 diagnosis. Among them, two had been negative on PCR twice and were discharged but subsequently became positive on PCR 2-4 weeks later and developed pneumonia. These patients were also positive for IgG antibody after the confirmed diagnosis based on PCR accompanied with the development of pneumonia. Our findings suggest an immune response delay to COVID-19 in immunocompromised patients, such as those with hematologic disorders. Thus, follow-up examinations with antibody testing are important in these patients.