LAUSR

Objectives Worldwide spread of COVID-19 disease highlights the need for assessment of long-term humoral immunity in convalescent subjects. Our objectives were to evaluate long-term IgG SARS-CoV-2 antibody response and B-cell memory response in COVID-19 convalescent subjects. Methods Blood samples were collected from a cohort of subjects recovering from COVID-19 disease and from healthy subjects that donated blood. SARS-CoV-2 IgG antibodies were quantitatively detected by ELISA using anti-S1 spike IgG. SARS-CoV-2 spike-specific IgG memory B-cells were evaluated in a randomly selected group of COVID-19 recovering subjects by reversed B-cell FluroSpot based on human IgG SARS-CoV-2 receptor-binding domain. Statistical analysis was performed with clinical variables and time post-COVID-19 infection. Results Antibody response was not detected in 26 of 392 (6.6%) COVID-19 convalescent subjects. Over a period of 9 months, the level of antibodies decreased by 50% but stabilized at 6 months and prevailed a protective level up to 9 months. No differences were found regarding IgG SARS-COV-2 antibody levels for age, gender, and major blood types, over-time. COVID-19 asymptomatic subjects did not differ in antibody level overtime from subjects with mild to severe disease. Repeated paired IgG SARS-COV-2 antibody level analyses disclosed that over 6 and 9 months, 15.3% (9 of 59) and 15.8% (3 of 19) of subjects became SARS-COV-2 IgG seronegative, respectively, all with low antibody level at 3 months. Rate of antibody decline was not affected by age, gender, or clinical symptomatology. In a subgroup of recovering subjects, memory B-cell response up to 9-months post COVID-19 infection, was undetectable in 31.8% (14/44) of subjects with no correlation to age, SARS-COV-2 antibody level, or time post-infection. Conclusions Majority of COVID-19 convalescent subjects develop IgG SARS-COV-2 antibody response that prevails a protective level over a period of up to 9-months regardless of age, gender, major blood types or clinical symptomatology.