Children are unlikely to have been the primary source of household SARS-CoV-2 infections

Yanshan Zhu; Conor J Bloxham; Katina D Hulme; Jane E Sinclair; Zhen Wei Marcus Tong; Lauren E Steele; Ellesandra C Noye; Jiahai Lu; Keng Yih Chew; Janessa Pickering; Charles Gilks; Asha C Bowen; Kirsty R Short

On the 31 st of December 2019, the World Health Organisation (WHO) was informed of a series of unknown pneumonia cases emerging in Wuhan City, Hubei Province, China. On the 7 th of January, 2020 the causative agent of these infections was identified as a novel coronavirus subsequently named SARS-CoV-2. This virus eventually spread to more than 180 different countries worldwide and in March 2020 the WHO declared SARS-CoV-2 a pandemic. At the time of writing (22 nd March, 2020) SARS-CoV-2 has infected >274,000 people resulting in >11,000 deaths. 1 Large data analyses have shown that the elderly are particularly susceptible to severe forms of COVID-19 (the clinical manifestation of SARS-CoV-2 infection). 2 However, disease severity and transmission amongst the paediatric population is less well defined. In an analysis of the 44,672 confirmed COVID-19 cases in China only 2·1% were found to be in children (≤19 years of age), 2 suggesting a reduced rate of infection in this age group. However, this observation remains controversial as others have suggested that the rate of SARS-CoV-2 infection in children under ten (7·4%) is similar to the population average (7·9%). 3 The current consensus is that clinical symptoms of COVID-19 are, on average, milder in children (although severe infections can still occur). [4] [5] [6] [7] [8] Such observations are consistent with the lower incidence of severe disease amongst children following infection with other coronaviruses including severe acute respiratory distress syndrome (SARS) or Middle East respiratory syndrome (MERS). 9, 10 However, this lower incidence of clinical symptoms (and therefore lower incidence of detected disease) raises concerns that children could be an important source of SARS-CoV-2 in household transmission clusters. 8 retrieved and reviewed (available in either English or Chinese). Of these, 126 articles were excluded because i) they did not report paediatric infections ii) did not report sufficient individual case data and/or iii) did not report family clusters. Individual paediatric patient data was obtained from the reviewed studies and was only excluded if the individual was recorded as having leukaemia (n = 1) or if the blood panel data was descriptive, rather than numerical (e.g. 'elevated platelets') (n=10). The intra-household transmission clusters were also sourced from information provided by local health authority's news of China, Europe, France, Germany, Italy, Japan, and South Korea when available. Any intra-household cluster identified in these local sources was included in the study.