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Little is known about the nature and durability of the humoral immune response to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
We measured antibodies in serum samples from 30,576 persons in Iceland, using six assays (including two pan-immunoglobulin [pan-Ig] assays), and we determined that the appropriate measure of seropositivity was a positive result with both pan-Ig assays. We tested 2102 samples collected from 1237 persons up to 4 months after diagnosis by a quantitative polymerase-chain-reaction (qPCR) assay. We measured antibodies in 4222 quarantined persons who had been exposed to SARS-CoV-2 and in 23,452 persons not known to have been exposed.
Of the 1797 persons who had recovered from SARS-CoV-2 infection, 1107 of the 1215 who were tested (91.1%) were seropositive; antiviral antibody titers assayed by two pan-Ig assays increased during 2 months after diagnosis by qPCR and remained on a plateau for the remainder of the study. Of quarantined persons, 2.3% were seropositive; of those with unknown exposure, 0.3% were positive. We estimate that 0.9% of Icelanders were infected with SARS-CoV-2 and that the infection was fatal in 0.3%. We also estimate that 56% of all SARS-CoV-2 infections in Iceland had been diagnosed with qPCR, 14% had occurred in quarantined persons who had not been tested with qPCR (or who had not received a positive result, if tested), and 30% had occurred in persons outside quarantine and not tested with qPCR.
Our results indicate that antiviral antibodies against SARS-CoV-2 did not decline within 4 months after diagnosis. We estimate that the risk of death from infection was 0.3% and that 44% of persons infected with SARS-CoV-2 in Iceland were not diagnosed by qPCR.
N. Engl. J. Med 2020 Sep 01;[EPub Ahead of Print], DF Gudbjartsson, GL Norddahl, P Melsted, K Gunnarsdottir, H Holm, E Eythorsson, AO Arnthorsson, D Helgason, K Bjarnadottir, RF Ingvarsson, B Thorsteinsdottir, S Kristjansdottir, K Birgisdottir, AM Kristinsdottir, MI Sigurdsson, GA Arnadottir, EV Ivarsdottir, M Andresdottir, F Jonsson, AB Agustsdottir, J Berglund, B Eiriksdottir, R Fridriksdottir, EE Gardarsdottir, M Gottfredsson, OS Gretarsdottir, S Gudmundsdottir, KR Gudmundsson, TR Gunnarsdottir, A Gylfason, A Helgason, BO Jensson, A Jonasdottir, H Jonsson, T Kristjansson, KG Kristinsson, DN Magnusdottir, OT Magnusson, LB Olafsdottir, S Rognvaldsson, L le Roux, G Sigmundsdottir, A Sigurdsson, G Sveinbjornsson, KE Sveinsdottir, M Sveinsdottir, EA Thorarensen, B Thorbjornsson, M Thordardottir, J Saemundsdottir, SH Kristjansson, KS Josefsdottir, G Masson, G Georgsson, M Kristjansson, A Moller, R Palsson, T Gudnason, U Thorsteinsdottir, I Jonsdottir, P Sulem, K Stefansson