The role of children in the spread of COVID-19: Using household data from Bnei Brak, Israel, to estimate the relative susceptibility and infectivity of children

Abstract

One of the significant unanswered questions about COVID-19 epidemiology relates to the role of children in transmission. In this study we estimate susceptibility and infectivity of children compared to those of adults. Understanding the age-structured transmission dynamics of the outbreak provides precious and timely information to guide epidemic modelling and public health policy. Data were collected from households in the city of Bnei Brak, Israel, in which all household members were tested for COVID-19 using PCR. To estimate relative transmission parameters in the absence of data on who infected whom, we developed an estimation method based on a discrete stochastic dynamic model of the spread of the epidemic within a household. The model describes the propagation of the disease between household members allowing for susceptibility and infectivity parameters to vary among two age groups. The parameter estimates are obtained by a maximum likelihood method, where the likelihood function is computed based on the stochastic model via simulations. Inspection of the data reveals that children are less likely to become infected compared to adults (25% of children infected over all households, 44% of adults infected over all households, excluding index cases), and the chances of becoming infected increases with age. An interesting exception is that infants up to age one year are more likely to be infected than children between one and four. Using our modelling approach, we estimate that the susceptibility of children (under 20 years old) is 45% [40%, 55%] of the susceptibility of adults. The infectivity of children was estimated to be 85% [65%,110%] relative to that of adults. It is widely observed that the percentage of children within confirmed cases is low. A common explanation is that children who are infected are less likely to develop symptoms than adults, and thus are less likely to be tested. We estimate that children are less susceptible to infection, which is an additional factor explaining their relatively low rate of occurrence within confirmed cases. Moreover, our results indicate that children, when infected, are somewhat less prone to infect others compared to adults; however, this result is not statistically significant. The resulting estimates of susceptibility and infectivity of children compared to adults are crucial for deciding on appropriate interventions, and for controlling the epidemic outbreak and its progress. These estimates can guide age-dependent public health policy such as school closure and opening. However, while our estimates of children's susceptibility and infectivity are lower than those of adults within a household, it is important to bear in mind that their role in the spread of COVID-19 outside the household, is also affected by different contact patterns and hygiene habits.

Susceptibility to SARS-CoV-2 Infection Among Children and Adolescents Compared With Adults

“…A total of 18 studies were contact-tracing studies (CTSs), 7,10,12,16-31 with 3 based in schools, [29][30][31] and 14 studies were population screening studies. 7, [32][33][34][35][36][37][38][39][40][41][42][43][44][45] Two were high quality, 33,35 22 were medium quality, 10,12,16,21,22,[24][25][26][27][29][30][31][32]34,36,38,[40][41][42][43][44][45] 7 were low quality, [17][18][19][20]23,28,39 and 1 was uncertain quality. 7,37…”

“…χ 2 Test suggested this group difference was significant (χ 2 = 4.54; P = .03). When only the 8 high-quality and medium-quality studies with low risk of bias were examined, 10,12,16,21,[24][25][26][27] this finding was no longer significant (OR, 0.68; 95% CI, 0.41-1.11); however, the difference in estimates between low-quality studies and high-quality and medium-quality studies was not significant (eFigure 1 in the Supplement). We hypothesized that CTSs including only household contacts might provide a clearer indication of the relative susceptibility to infection of children vs adults because all contacts within households might be assumed to receive a similar exposure to infection from index cases.…”

“…A total of 6 studies were from mainland China, 10,16,18,20,22,24 2 from the US, 25,26 and 1 each from Taiwan, 17 Japan, 19 South Korea, 12 Israel, 21 the Netherlands, 7,28 Brunei, 27 and India, 23 with 3 CTSs based in schools from Australia, 29 Ireland, 30 and Singapore. 31 Lower secondary attack rates in children and adolescents compared with adults were reported by 11 studies: 5 from provinces of China, including Hunan, 10,22 Hubei, 16,18 and Beijing, 20 and 6 from other countries, including Taiwan, 17 Japan, 19 the US, 25,26 Israel, 21 and the Netherlands, 7,28 although confidence intervals were wide in some studies. No significant differences in secondary attack rates by age were reported in 3 studies from Guangdong province, China, 24 Brunei, 27 and the states of Tamil Nadu and Andhra Pradesh in India, 23 with 1 study from South Korea 12 reporting high secondary attack rates in those younger than 19 years.…”

Measures to maintain regular operations and prevent outbreaks of SARS-CoV-2 in childcare facilities or schools under pandemic conditions and co-circulation of other respiratory pathogens

“…Less frequently, individual children or students whose parents were also often sick and were considered vectors [ 31 ], [ 57 ]. Children have so far not appeared as so-called “superspreaders” in schools and day-care centres or within families [ 29 ], [ 58 ], [ 59 ], [ 60 ], [ 61 ]. A more detailed analysis of the transmission paths in terms of a structured outbreak analysis is missing.…”

“…Israel, Sweden or the USA), the number of infections in the general population was rising, in some cases significantly, so that the question of the causal relationships between infections in pupils through private or school transmissions and the cause of the infections in caregivers or staff remained unanswered [ 38 ], [ 40 ], [ 56 ]. Other aspects of specific risks in children and adolescents, such as the membership of families in population groups with religiously or ideologically motivated rejection of the hygiene measures [ 59 ], [ 62 ] or contradictory recommendations of the responsible health authorities with a simultaneously increased risk of mobility (USA) [ 63 ], [ 64 ] also make it difficult to draw general conclusions about the role of children and adolescents. The authors of a recent report on an outbreak at a secondary school in Israel emphasize that in the overcrowded school classes (>30 pupils), the wearing of mouth and nose covers and frequent airing were not consistently adhered to due to the high outside temperatures (40°C and more) (the air conditioning system was constantly in operation with no information on air exchange rates) [ 65 ].…”