SARS-CoV-2 infection in households with and without young children: Nationwide cohort study, Denmark, 27 February 2020 to 26 February 2021

Background: Infections with seasonally spreading coronaviruses are common among young children dur-ing winter months in the northern hemisphere; the immunological response lasts around a year. However, it is not clear if living with young children changes the risk of SARS-CoV-2 infection among adults. Aim: Our aim was to investigate the association between living in a household with younger children and the risk of SARS-CoV-2 infections and hospitalisation. Methods: In a nationwide cohort study, we followed all adults in Denmark aged 18 to 60 years from 27 February 2020 to 26 February 2021. Hazard ratios of SARS-CoV-2 infection by number of 10 months to 5 year-old children in the household were estimated using Cox regression adjusted for adult age, sex and other potential confounders. In a sensitivity analy-sis, we investigated the effect of the children's age. Results: Among 450,007 adults living in households with young children, 19,555 were tested positive for SARS-CoV-2, while among 2,628,500 adults with-out young children in their household, 110,069 were tested positive for SARS-CoV-2 (adjusted hazard ratio (aHR) = 1.10; 95% confidence interval (CI): 1.08-1.12). Among adults with young children, 620 were hospital-ised with SARS-CoV-2, while 4,002 adults without chil-dren were hospitalised with SARS-CoV-2 (aHR = 0.97; 95% CI: 0.88-1.08). Sensitivity analyses found that an increasing number of younger children substantially increased the risk of SARS-CoV-2 infection but not hospitalisation. Conclusion: Living in a household with young children was associated with a small increased risk of SARS-CoV-2 infection.