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.
Keywords: COVID-19 disease; IgA; IgG; IgM; SARS-CoV-2; asthma; memory B cells; memory T cells; population-based cohort; risk factors; young adults.
【저자키워드】 SARS-CoV-2, IgG, IgM, Asthma, Risk factors, memory B cells, COVID-19 disease, IgA, memory T cells, Young adults., population-based cohort, 【초록키워드】 COVID-19, coronavirus disease, Asthma, Coronavirus disease 2019, coronavirus, vaccination, Risk factors, Immunity, T cells, SARS-COV-2 infection, T-cell Response, Infection, memory B cells, Sex, risk, Symptom, smoking, severe acute respiratory syndrome Coronavirus, ELISA, COVID-19 disease, asymptomatic infections, Adults, Cohort, body mass index, Health, IgE, Characteristics, Asymptomatic, cellular immunity, memory T cells, Seropositivity, Mild, allergy, age, ELISPOT, Follow-up, public transport, T-cell, respiratory, assessment, disease, seropositive, seronegative, T-cell responses, humoral and cellular immunity, population-based cohort, memory response, IgG titer, humoral, mild to moderate, body mass, Transport, acute respiratory syndrome, Factor, birth cohort, acute respiratory syndrome coronavirus, acute respiratory syndrome coronavirus 2, mild to moderate disease, moderate disease, subject, individual, participant, binding domain, positive, rhinitis, specific IgM, IgG titers, subpopulation, memory T, milieu, Effects, memory B, Barn, whom, IMPROVE, detectable, conducted, indicate, subjects, Swedish, subset, seropositive subject, symptomatic and asymptomatic, 【제목키워드】 T-cell immunity, Swedish,