Aim: This pilot study explored signs of immunological cross-reactivity between SARS-CoV-2 and human coronaviruses (HCoVs) in a Swedish school setting.
Methods: A cross-sectional, hypothesis-generating study was conducted late 2020 before vaccines against COVID-19 were available. Forty-seven 7-8-year-old children, seventy-five 14-year-old adolescents, fifty-four 17-year-old adolescents, and 52 adult school staff were included, and immune responses to SARS-CoV-2 and HCoVs were assessed.
Results: The SARS-CoV-2 seroprevalence was high in the older age groups (33%-41%). Seropositive individuals had significantly higher levels of antibodies against betacorona virus compared to seronegative individuals. SARS-CoV-2 seropositivity was rare among the 7-8-year-old children despite the high endemic context. SARS-CoV-2-specific T-cell responses in the absence of SARS-CoV-2-specific antibodies were seen in all age groups.
Conclusion: The data support a role for cross-reactive immune responses induced by recent HCoV infections, with cross-reactive T-cell responses providing protection against COVID-19 in young children.
Keywords: COVID‐19; SARS‐CoV‐2; children; immune response; school.
© 2026 The Author(s). Acta Paediatrica published by John Wiley & Sons Ltd on behalf of Foundation Acta Paediatrica.