Longitudinal follow-up of IgG anti-nucleocapsid antibodies in SARS-CoV-2 infected patients up to eight months after infection

Van Elslande, Jan; Oyaert, Matthijs; Ailliet, Scott; Van Rans, Marc; Lorent, Natalie; Vande Weygaerde, Yannick; Andr, Emmanuel; Lagrou, Katrien; Vandendriessche, Stien; Vermeersch, Pieter

BACKGROUND: Most SARS-CoV-2 infected patients develop IgG antibodies within 2-3 weeks after symptom onset. Antibody levels have been shown to gradually decrease in the first months after infection, but few data are available at six months or later. METHODS: A retrospective multi-center study was performed using 652 samples of 236 PCR-confirmed SARS-CoV-2 infected patients from 2 Belgian University hospitals. Patients were included if at least two samples were available (range 2-7 samples); including at least one sample collected 30 days or later after first positive PCR (range 0-240 days). Of those 236 patients, 19.1% were classified as mild/asymptomatic (mild) and 80.9% as moderate to critical (severe). IgG anti-nucleocapsid antibodies (anti-N) were measured using the Abbott Architect immunoassay. RESULTS: 22.2% of mild and 2.6% of severe COVID-19 cases never seroconverted (p < 0.001). Of the mild patients who seroconverted 0-59 days after PCR; 18.8%, 40.0% and 61.1% were seronegative in the windows 60-119 days, 120-179 days and 180-240 days after PCR, respectively. In severe patients, these numbers were 1.9%, 10.8% and 29.4% respectively (p < 0.05 each). Antibody levels were significantly higher in severe patients compared to mild patients in each 60 day window (p < 0.001 each). CONCLUSIONS: SARS-CoV-2 anti-N IgG antibody levels steadily decreased after 2 months up to 8 months post PCR. Of severe COVID-19 patients, 70.6% remained positive up to eight months after infection. Antibody levels were significantly lower in mild SARS-CoV-2 infected patients and 61.1% became seronegative within 6 months after the first positive PCR.