The worldwide outbreak of Severe Acute Respiratory Syndrome Coronavirus 2 (SARSCoV2) has caused a pandemic of Coronavirus Disease 2019 (COVID19), killing more than 6.26 million people. The home is an exposed environment at high risk of SARSCoV2 infection, and the role of children in the spread of the virus is unknown.
A new study published in the International Journal of Infectious Diseases systematically reviews the literature. We perform meta-analyses to assess the prevalence of pediatric COVID19 in family clusters, estimate secondary infection rates for children in households, and compare SARSCoV2 infection rates in different age groups.
Background
People around the world are still suffering from the fourth wave of pandemics caused by the Omicron variant of SARSCoV2. Breaking the chain of transmission of the virus, along with vaccination, is an effective way to combat the outbreak. Studies show that households are the highest-risk exposure environment and may contribute to the rapid increase in COVID 19 cases even after social distance policies and national blockades.
Infectious respiratory diseases such as influenza and measles are often transmitted from children to adults, but it is unclear whether SARSCoV2 is transmitted in this way. Children may be responsible for the continued spread of the virus, as they are often asymptomatic carriers. In fact, with the advent of new variants (such as Delta and Omicron), an increase in infection by children has been observed. Therefore, it is important to better understand the role of children in household viral infections.
A New Study
The Preferred Reporting Items for Systematic Reviews and MetaAnalyses (PRISMA) guidelines were followed to conduct this study. Two or more confirmed COVID19 cases among individuals where the diagnosis of cases occurred within 2 weeks of each other, identified a household transmission cluster. The household contacts were not the 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 SARSCoV2. The number of secondary cases in a household divided by the total number of contacts in the household was defined as the secondary incidence rate (SAR) in the household. People under the age of 18 were defined as children.
A systematic search was conducted on PubMed and EMBASE from the beginning until April 20, 2022, using specific key search terms and excluding non-primary sources and modelling studies. Case analysis of pediatric home infections and a meta-analysis of SAR were two parts that included the study. The case analysis and meta-analysis contained 47 and 48 articles, respectively.
Key Findings
Researchers observed that primary and secondary child cases constituted only a small proportion of the household transmission in case analyses. Findings like this suggest that children are unlikely to be the main cause of infection in familial clusters. Consistent with previous meta-analyses, scientists observed lower household transmissibility in both pediatric index cases and secondary contacts, compared to adults. Based on these findings, children may be less susceptible to COVID19 than adults.
A marked difference was found between children under 10 years and those over 10 years, and consistent with another study, scientists found higher transmissibility among younger children. However, due to the limited number of studies, this difference lacks statistical power, suggesting the need for further future studies.
Scientists estimated the total SAR of pooled households for child index / primary and secondary cases to be 0.20 and 0.24, respectively. Lower household transmission rates were observed in both children and contact proband cases compared to adults. Subgroup analyzes of different variants and durations revealed an increase in SAR in children’s homes (Omicron: 0.56, Alpha: 0.42, Delta: 0.35, Wild: 0.20). In addition, there was no significant difference in home SAR between children and adults when the new subspecies prevailed.
Key Limitations of the Study
It is relatively inadequate and contains a limited number of articles. Due to this insufficiency, certain aspects of SAR, such as incubation and infection time, have not been fully studied. In some studies, the determination of the condition of the case may be uncertain, especially for the proband of an asymptomatic child. In addition, epidemiological information is self-reported and can be biased. Most importantly, significant unexplained heterogeneity has created a major obstacle to the interpretation of the results. Researchers have shown that qualitative conclusions may be more reliable compared to quantitative results and may limit the generalizability of the results.
Conclusion
Current studies show that children do not appear to dominate home infections, but as new variants continue to emerge, children’s infection rates have increased. Given the serious risk of complications from COVID 19 in children, the study and implementation of vaccination in children is very important.
