Researchers found a decrease in antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) over 60 days among health care personnel at the Vanderbilt University Medical Center in Nashville, Tennessee, according to a recent research letter published in JAMA.
To assess the duration of antibody response to SARS-CoV-2 infection in health care personnel, the study authors evaluated the change in mean and median signal-to-threshold ratios at baseline and 60 days in study participants who were seropositive at baseline and those who were seropositive vs seronegative at 60 days. Serum samples were tested for anti-SARS-CoV-2 antibodies using a validated enzyme-linked immunosorbent assay against the prefusion-stabilized extracellular domain of the SARS-CoV-2 spike protein. A specimen was considered reactive if the signal-to-threshold ratio at a serum dilution of 1:100 with background correction was greater than 1.0, with higher ratios indicating higher antibody titers.
Serum samples were collected at baseline from the first 249 volunteers (64.5% women; 91.6% White), with a median age of 33 years (range, 21-70 years); 230 volunteers (92%) returned for a second blood draw. Of the 249 participants, 19 (7.6%) had anti-SARS-CoV-2 antibodies detected at baseline, among whom 8 of participants (42%) had antibodies that persisted above the seropositivity threshold at 60 days and 11 (58%) became seronegative. Overall seropositivity changed from 7.6% at baseline (n=19) to 3.2% (n=8) at 60 days.
All 19 participants who were seropositive at baseline had antibody decreases at 60 day. Participants who remained seropositive at 60 days had a higher signal-to-threshold ratio at baseline (mean, 4.8; range, 1.9-6.2) but saw antibodies decline from the mean signal-to-threshold ratio at baseline to 2.3. Participants whose ratios decreased below threshold at 60 days (mean, 1.4; range, 1.1-2.3) saw antibodies decrease from baseline to 0.6 at 60 days.
“The consistency in decline in the signal-to-threshold ratio regardless of the baseline ratio and a higher [percentage] of asymptomatic participants becoming seronegative support the interpretation as a true decline over a 2-month period rather than an artifact of assay performance,” the study authors noted.
Limitations of the study included its single-center setting, small sample size, convenience sampling, and lack of information on timing of infection to evaluate antibody kinetics.
“Implications for health care personnel with antibodies assigned to care for infected patients depend on whether decline in these antibodies increases risk of reinfection and disease, which remains unknown, especially given the lack of data on memory B-cell and T-cell responses,” the study authors concluded.
Patel MM, Thornburg NJ, Stubblefield WB, et al. Change in antibodies to SARS-CoV-2 over 60 days among health care personnel in Nashville, Tennessee. Published online September 17, 2020. Letter. JAMA. doi:10.1001/jama.2020.18796