COVID-19 immunity in young adults with mild disease
Published: October 22, 2021
Young adults contribute substantially to the spread of SARS-CoV-2 infection and although most suffer from mild disease, there are concerns of long-term adverse health effects. The impact of COVID-19 disease and the population-level immunity against SARS-CoV-2 existing in young adults remain unclear.
In a recent article in The Journal of Allergy and Clinical Immunology (JACI), Björkander et al. conducted a study on unvaccinated 24–27-year-olds from the population-based cohort BAMSE in Stockholm, Sweden, between October 2020 and June 2021. They measured SARS-CoV-2 receptor-binding domain (RBD) -specific IgM, IgA and IgG titres by ELISA and explored disease characteristics, symptoms and epidemiological factors associated with these antibodies (n=980). They further measured SARS-CoV-2-specific B- and T-cell responses by ELISpot and Fluorospot in a subpopulation of participants (n=108).
The authors report that 28.4% of subjects were positive for at least one antibody isotype (seropositive), of which 18.4% were IgM single positive. About half of the seropositive individuals reported that they had been bedbound due to symptoms, but less than 1% were hospitalized. A majority reported reduced taste and/or smell. Fewer than one in ten had symptoms for more than four weeks and one in seven were 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 randomly selected samples, 20.7% and 35.0% had detectable SARS-CoV-2 specific memory B- and T-cell responses, respectively. Among seropositive subjects, 70% had detectable levels of memory B-cells, while 55% had memory T-cells. Of note, T-cell responses were detectable in 17.2% of seronegative subjects.
The continuously high surge of both symptomatic and asymptomatic infections among young adults highlights the need for continuing the large-scale vaccination campaign in this age group, the authors conclude. The study findings further suggest that assessment of IgM may improve population-based estimations of SARS-CoV-2 infection, and that the relatively low proportion of seropositive subjects with detectable cellular responses and the notable proportion of seronegative subjects with T-cell responses warrant further investigations. The authors will now continue to study the longevity of B- and T-cell immunity and the impact of vaccination in the BAMSE cohort.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.
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