Our understanding of the role of children in the spread of SARS-CoV-2 has rapidly changed over the last year. Initially, in the absence of clear evidence, it was assumed that transmission within schools would be likely to facilitate the spread of infection, as would be anticipated for an influenza pandemic.  School closure for the majority of children was part of the measures introduced in the first UK lockdown. Later it became clear that children had a very low risk of developing severe infection or complications of covid-19, and may not play a major role in SARS-CoV-2 transmission.  Balancing this new evidence with the substantial impact of schools closure on the wellbeing of children, schools in the UK remained open during the second national lockdown in November 2020. However, in the autumn and early winter of 2020 evidence from population-based samples showed that children and young people in fact had a prevalence of SARS-CoV-2 infection similar to, or higher than adults, and were often asymptomatic, suggesting that transmission within schools may play an important role in wider community spread. [3,4]
Against this backdrop our research group sought to investigate the overall role of contact with children on the risk of developing SARS-CoV-2 infection and serious outcomes from covid-19.  We used pseudonymised GP records for nearly 12 million people across England and categorised households by whether people lived with children or not. For, separating, the first and second waves of the UK pandemic, we determined the risks for adults who lived with children of pre-school and primary school age, secondary school age, or both, compared to adults who did not live with children. Our results showed no or minimal associations during the first wave. However, during the second wave we found an increased risk of SARS-CoV-2 infection and hospital admission for adults who lived with children, although the absolute increase in outcomes were low. Triangulating our results, similar findings were seen among the Danish population during 2020, with the highest risks to adults who lived with children in the period after lockdown. 
Despite these temporal associations we cannot be confident our findings are caused by schools remaining open during the second wave. There may be other differences between adults who live with children and those who don’t, providing greater opportunities for adult to adult transmission such as in playgrounds, more frequent shopping, or working outside of home if not home-schooling.
As this paper is published, children in England have now been back at school for up to two weeks, too early to tell if there will be an important uptick in cases. An important difference compared to 2020 is that a large proportion of those at highest risk of severe outcomes from covid-19 have received at least one dose of vaccine, limiting the potential for adverse outcomes from increased transmission within schools. In addition, schools have worked hard to minimise risk of transmission with measures including lateral flow testing of secondary school age children.
Ultimately, school reopening is a balance of risks and harms, and undoubtedly children have suffered a great deal over the last year. The small increases in risk we have identified across the whole population, even if casually associated with school transmission, must be balanced against the benefits of children returning to education. However, we hope that our research serves as a timely reminder of not letting the guard down now: we must continue to minimise opportunities for SARS-CoV-2 transmission by adhering to current guidelines as the vaccine programme continues.
Harriet Forbes, assistant professor, London School of Hygiene and Tropical Medicine.
Laurie Tomlinson, associate professor, London School of Hygiene and Tropical Medicine. Twitter: @roxytonin
Competing interests: see full declaration on research paper.
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- Viner RM, Mytton OT, Bonell C, et al. Susceptibility to SARS-CoV-2 Infection Among Children and Adolescents Compared With Adults: A Systematic Review and Meta-analysis. JAMA Pediatr Published Online First: 25 September 2020. doi:10.1001/jamapediatrics.2020.4573
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