Antibody levels remain high to one-year’s follow-up after moderate and severe COVID-19, but not after mild cases

Abstract

Background

Understanding the longevity of antibodies against SARS-CoV-2 infection is of utmost importance in predicting the further course of the pandemic and to plan vaccination strategies. Here we report a cohort of COVID-19 patients with different disease severities whose antibody dynamics we evaluated during one-year of follow-up.

Methods

We conducted a longitudinal study of 123 COVID-19 patients and 45 SARS CoV-2 negative outpatients with upper respiratory tract infection. We analyzed the demographic and clinical features of the patients with COVID-19 in relation to different disease severities according to the WHO classification. The antibody response was evaluated by a Luciferase Immunoprecipitation System (LIPS) assay at 3, 6, and 12 months after the acute infection.

Results

Amongst the enrolled COVID-19 patients, 15 (12%) had mild, 42 (34%) had moderate, 39 (32%) had severe and 27 (22%) had critical disease courses; 79% of the patients were hospitalized. During follow-up, all patients had anti-SARS RBD-IgG levels above the cut-off value on all visits, but the antibody levels varied significantly between the different disease severity groups. Between the six- and 12-month follow-up visits, 41% of patients were vaccinated, which enhanced their antibody levels significantly.

Conclusion

Our data demonstrate sustained antibody levels at one-year after moderate and severe COVID-19 infection. Vaccination of patients with the mild disease is important to raise the antibody levels to a protective level.

Keywords:

• COVID-19
• SARS CoV-2
• the WHO classification
• RBD-IgG antibodies
• one-year follow-up
• vaccination

Acknowledgements

We would like to thank the following colleagues: Annika Häling and Meeri Jürgenson for their help performing LIPS assays, Anne Krips, who aliquoted and stored samples for this study, and Külli Miljukov for help with follow-up visits. Most of all, we thank all the study participants who participated in this study.

Disclosure statement

The authors have no conflicts of interest to declare.

Additional information

Funding

The study was supported by the basic research fund of the Department of Internal Medicine, Institute of Clinical Medicine of University of Tartu and by RITA2/126 (HOSPICOVI) a project financed by the Estonian Research Council.