Humoral Immune Response to SARS-CoV-2 in Iceland
Daníel F. Guðbjartsson, Gudmundur L. Norddahl, Páll Melsted, Kristbjörg Gunnarsdóttir, Hilma Hólm, Elías Eyþórsson, Asgeir Ö. Arnthórsson, Daði Helgason, Kristbjörg Bjarnadóttir, Ragnar Freyr Ingvarsson, Brynja Thorsteinsdottir, Steinunn Kristjánsdóttir, Kolbrún Birgisdottir, Anna M. Kristinsdottir, Martin I. Sigurðsson, Gudny A. Arnadottir, Erna V. Ivarsdottir, Margrét B. Andrésdóttir, Frosti Jónsson, Arna B. Agustsdottir, Jonas Berglund, Berglind Eiríksdottir, Rún Friðriksdóttir, Elisabet E Gardarsdottir, Magnús Gottfreðsson, Olafia S. Gretarsdottir, Steinunn Guðmundsdóttir, Kjartan R. Guðmundsson, Thora R Gunnarsdottir, Arnaldur Gylfason, Agnar Helgason, Brynjar Ö. Jensson, Áslaug Jónasdóttir, Hákon Jónsson, Þórður Kristjánsson, Karl G. Kristinsson, Droplaug N. Magnúsdóttir, Ólafur Þ. Magnússon, Lovisa Bjork Olafsdóttir, Sölvi Rögnvaldsson, Louise le Roux, Guðrún Sigmundsdóttir, Ásgeir Sigurðsson, Garðar Sveinbjörnsson, Kristin E. Sveinsdottir, Maney Sveinsdottir, Emil Aron Thorarensen, Bjarni Thorbjornsson, Maríanna Þórðardóttir, Jona Saemundsdottir, Sigurður Kristjánsson, Kamilla S. Josefsdottir, Gísli Másson, G. Georgsson, Már Kristjánsson, Alma D. Möller, Runólfur Pálsson, Þórólfur Guðnason, Unnur Þorsteinsdóttir, Ingileif Jónsdóttir, Patrick Sulem, Kāri Stefánsson
Abstract
BACKGROUND: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.