SARS-CoV-2-specific B- and T-cell immunity in a population-based study of young Swedish adults.

Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden. Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; Center of Occupational and Environmental Medicine, Region Stockholm, Stockholm, Sweden. Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. Division of Clinical Immunology and Transfusion Medicine, Department of Laboratory Medicine, Karolinska Institutet at Karolinska University Hospital, Stockholm, Sweden. Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden; Sachs' Children and Youth Hospital, Södersjukhuset, Stockholm, Sweden. Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden; Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; Sachs' Children and Youth Hospital, Södersjukhuset, Stockholm, Sweden. Electronic address: erik.melen@ki.se. Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden. Electronic address: qiang.pan-hammarstrom@ki.se.

The Journal of allergy and clinical immunology. 2022;(1):65-75.e8

Abstract

BACKGROUND Young adults are now considered major spreaders of coronavirus disease 2019 (COVID-19) disease. Although most young individuals experience mild to moderate disease, there are concerns of long-term adverse health effects. The impact of COVID-19 disease and to which extent population-level immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exists in young adults remain unclear. OBJECTIVE We conducted a population-based study on humoral and cellular immunity to SARS-CoV-2 and explored COVID-19 disease characteristics in young adults. METHODS We invited participants from the Swedish BAMSE (Barn [Children], Allergy Milieu, Stockholm, Epidemiology) birth cohort (age 24-27 years) to take part in a COVID-19 follow-up. From 980 participants (October 2020 to June 2021), we here present data on SARS-CoV-2 receptor-binding domain-specific IgM, IgA, and IgG titers measured by ELISA and on symptoms and epidemiologic factors associated with seropositivity. Further, SARS-CoV-2-specific memory B- and T-cell responses were detected for a subpopulation (n = 108) by ELISpot and FluoroSpot. RESULTS A total of 28.4% of subjects were seropositive, of whom 18.4% were IgM single positive. One in 7 seropositive subjects was asymptomatic. Seropositivity was associated with use of public transport, but not with sex, asthma, rhinitis, IgE sensitization, smoking, or body mass index. In a subset of representative samples, 20.7% and 35.0% had detectable SARS-CoV-2 specific B- and T-cell responses, respectively. B- and T-cell memory responses were clearly associated with seropositivity, but T-cell responses were also detected in 17.2% of seronegative subjects. CONCLUSIONS Assessment of IgM and T-cell responses may improve population-based estimations of SARS-CoV-2 infection. The pronounced surge of both symptomatic and asymptomatic infections among young adults indicates that the large-scale vaccination campaign should be continued.

Methodological quality

Publication Type : Clinical Trial

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