What role do children play in family transmission of COVID-19?
The global outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to the coronavirus disease 2019 (COVID-19) pandemic and claimed more than 6.26 million lives. Households represent a high-risk exposure setting for SARS-CoV-2 transmission, and the role of children in spreading the virus is not known.
A new study published in the International Journal of Infectious Diseases systematically reviews the literature. He is performing a meta-analysis to assess the prevalence of pediatric COVID-19 in family groups, estimate the secondary attack rate of children in households, and compare the transmissibility of SARS-CoV-2 in different age groups.
Study: The role of children in the familial transmission of COVID-19: a systematic review and meta-analysis. Image Credit: Halfpoint / Shutterstock
Globally, people are still suffering from the fourth wave of the pandemic, caused by the Omicron variant of SARS-CoV-2. Besides vaccination, breaking the chain of transmission of the virus is an effective way to control the epidemic. Research has shown that the household is perhaps the most at-risk exposure setting and could have contributed to a sharp escalation in COVID-19 cases even after the social distancing policy and nationwide shutdowns.
Infectious respiratory diseases such as influenza and measles are often transmitted from children to adults, but it is not known whether SARS-CoV-2 is transmitted this way. Children could be responsible for the continued spread of the virus, frequently being asymptomatic carriers. In fact, increased transmission by children has been observed with the emergence of new variants (eg, Delta and Omicron). It is therefore essential to better understand the role played by children in household viral transmission.
A new study
PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed in conducting this study. Two or more confirmed cases of COVID-19 among people in whom case diagnosis occurred within 2 weeks of each other identified a household transmission cluster. Family contacts were not family members who necessarily lived together. Instead, they were defined as close contacts who had unprotected contact with the index/primary case.
The secondary attack rate was used to empirically estimate the transmissibility of SARS-CoV-2. The number of secondary cases in households divided by the total number of household contacts was defined as the secondary attack rate (SAR) in households. Persons under the age of 18 were defined as children.
Systematic retrieval was performed on PubMed and EMBASE from inception to April 20, 2022, using specific key search terms and excluding non-primary papers and modeling studies. The case analyzes of domestic pediatric infections and the RAS meta-analysis were the two parts in which the studies were included. 47 and 48 articles were included for case review and meta-analyses, respectively.
The researchers observed that primary and secondary child cases constituted only a small proportion of household transmission in the case analyses. Findings like this suggest that children are unlikely to be the primary cause of infection in family clusters. Consistent with previous meta-analyses, scientists observed lower household transmissibility in pediatric index cases and secondary contacts, compared to adults. Based on these results, children might be less susceptible to COVID-19 than adults.
A marked difference was found between children under 10 years old and those over 10 years old, and in line with another study, scientists found higher transmissibility in younger children. However, due to the limited number of studies, this difference lacked statistical power, suggesting the need for further future studies.
The scientists estimated that the total pooled household SAR for index children/primary cases and secondary cases was 0.20 and 0.24. In both child and contact index cases, lower household transmissibility was observed compared to adults. Subgroup analyzes of different variants and time periods were performed and this revealed an increase in household DAS in children (Omicron: 0.56, Alpha: 0.42, Delta: 0.35, Wild: 0, 20). Moreover, when new variants dominated, no significant difference was found in household DAS between children and adults.
Main limitations of the study
A relatively insufficient and limited number of articles were included. Due to this insufficiency, some aspects of RAS have not been well explored, including incubation and infectious periods. In some studies, determination of case status may be uncertain, particularly in asymptomatic index cases in children. In addition, epidemiological information is subject to bias because it was self-reported. More importantly, significant unexplained heterogeneity was a significant hurdle when interpreting the results. The researchers said qualitative findings may be more reliable than quantitative results, which limits the generalizability of the findings.
The current study documents that although children do not appear to be dominant in family transmission, their transmissibility increased as new variants continued to emerge. Research and implementation of vaccination in children is extremely important, given the risks of serious complications posed by pediatric COVID-19.