SARS-CoV-2 infection in households with and without young children: Nationwide cohort study

Husby, A.; Corn, G.; Krause, T. G.

Background Infections with seasonally spreading human coronaviruses (HCoVs) are common among young children during winter months in the northern hemisphere, with immunological response lasting around a year. However, it is not clear whether recent household exposure to HCoVs reduces the risk of SARS-CoV-2 infection. Methods In a nationwide cohort study we followed all adults in Denmark aged 18 to 60 years from February 27 to November 15, 2020. Hazard ratios of SARS-CoV-2 infection by number of young children aged ten months to five years living in the household were estimated using Cox regression adjusted for adult age, gender, and other potential confounders. In sensitivity analyses we investigated the effect of age of children in the household, number of children living outside of the household, and number of other adult household-members. Results Among 449,915 adults in Denmark living in households with young children, 5,761 were tested positive for SARS-CoV-2, while among 2,629,821 adults without young children in their household, 33,788 were tested positive for SARS-CoV-2 (adjusted hazard ratio, 1.05; 95% confidence interval, 1.02 to 1.09). Sensitivity analyses of age of children in the household, number of children living outside of the household, and number of additional adult household members found increasing number of children, and especially increasing number of older children, to substantially increase the risk of SARS-CoV-2 infection. Conclusions Living in a household with young children was not associated with decreased risk of SARS-CoV-2 infection, thereby suggesting no strong preventive effect of recent exposure to HCoVs against SARS-CoV-2 infection.