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

Abstract

Background Young adults are now considered major spreaders of COVID-19 disease. Although most young individuals suffer from 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 SARS-CoV-2 exist in young adults remain unclear. Objective To conduct a population-based study on humoral and cellular immunity to SARS-CoV-2 and explore COVID-19 disease characteristics in young adults. Methods We invited participants from the Swedish BAMSE birth cohort (age 24-27 years) to take part in a COVID-19 follow-up. From 980 participants (October 2020-June 2021), we here present data on SARS-CoV-2 RBD-specific IgM, IgA and IgG titres measured by ELISA and on symptoms and epidemiological 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 28.4% of subjects were seropositive of which 18.4% were IgM single positive. One in seven seropositive subjects were asymptomatic. Seropositivity associated with use of public transport, but not with sex, asthma, rhinitis, IgE-sensitization, smoking or BMI. 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. Conclusion 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 should imply a continuation of the large-scale vaccination campaign.

Long-term T cell perturbations and waning antibody levels in individuals needing hospitalization for COVID-19

“…We found that all COVID-19 patients developed SARS-CoV-2 antigen specific T cells, that increased over time. Our findings are in accordance with other studies that have shown that SARS-CoV-2 infection results in increased expansion of antigen specific CD4 + and CD8 + T cell subsets [63, 94]. It is still unclear if the lower antigen specific responses seen at 2 and 6 weeks compared to 6-7 months are due to an overall immunosuppression [95] or a natural development of the immune response over time [65].…”

“…In our cohort, we found that the SARS-CoV-2 nucleocapsid-specific and spike-specific neutralizing antibody levels lasted 6-8 months post infection, even though there was a drastic decline at some time point after 6 weeks. Our findings are supported by Björkander et al [94], who have reported that the antibody responses lasted up to 8 months among young adults.…”

Association of Short-term Air Pollution Exposure With SARS-CoV-2 Infection Among Young Adults in Sweden

“…Potential limitations include exposure misclassification given that we estimated exposure to outdoor air pollution, whereas information on microclimate differences in exposure or time-activity patterns (eg, time spent in traffic and indoors) was not available. In addition, we investigated predisposition factors in a relatively small group of participants with only mild to moderate disease, 20 which limited the statistical power. Owing to the high correlations between air pollutants, we did not test the 2-pollutant model to assess the independence of each pollutant.…”

“… 22 Clinical data and self-reported COVID-19–related respiratory symptoms were obtained from questionnaire data. 20 This study was approved by the Swedish Ethical Review Authority, and all participants gave written informed consent. This study adhered to the Strengthening the Reporting of Observational Studies in Epidemiology ( STROBE ) reporting guideline with a completed checklist for observational studies in epidemiology.…”

The (apparent) antibody paradox in COVID-19

“…There are excellent T cell responses to the virus 6 months later [ 135 , 137 ] and T cell responses persist in spite of waning antibody responses [ 138–140 ]. A recent community-based survey from Sweden showed 17% of patients with T cell responses to SARS-CoV-2 were seronegative [ 141 ]. This highlights the importance of diagnostic T cell assays for SARS-CoV-2.…”