SINGAPORE: Children under the age of five are at “lowest risk” of contracting COVID-19 from adults, according to a Singapore study of household transmission of the virus.
The study by KK Women’s and Children’s Hospital (KKH) drew on data of children who were household contacts of COVID-19 cases and were screened for the disease at the hospital between March and April.
A total of 213 children under the age of 16 were screened for COVID-19 during this period. They came from 137 households with a total of 223 adults who were confirmed cases, according to the study.
Of the 213 children evaluated, 13 cases of adult-to-child COVID-19 transmission were detected across seven households.
This amounted to an “attack rate” of 6.1 per cent among children and 5.2 per cent of the households with confirmed exposure to COVID-19, the study found.
Further analysis showed that the adult-to-child transmission rate for children under the age of five was 1.3 per cent.
This was the lowest rate among all age groups, compared to 8.1 per cent for children aged five to nine, and 9.8 per cent for children aged 10 to 16.
The findings were published in October in the Journal of Pediatrics.
The study also found that the risk of secondary infection in children was highest if the index COVID-19 patient was the child’s mother. At 11.1 per cent, the rate was almost double that if the index case was a father or grandparent.
“Because population susceptibility to SARS-CoV-2 is assumed to be universal, the attack rate in children would be expected to be similar to that in adults,” the authors of the study wrote.
“Because transmission is known to be correlated with degree of contact, attack rates might be expected to be higher in younger children, who presumably have closer interactions with their parents than do older children.
“However, in our study the attack rate was lowest in the youngest age group,” the study's authors wrote.
Dr Yung Chee Fu, a consultant at KKH’s Infectious Disease Service and a co-author of the study, said that younger children might have more resistance to COVID-19 infection.
“It is possible that younger children are more resistant to SARS-CoV-2 infection at a cellular level,” he said in an Oct 13 newsletter about the study on KKH’s website.
Dr Yung made reference to studies that have found a trend of “increased expression”, as age increases, of an enzyme receptor in the nasal epithelium that is used by the coronavirus for host entry.
The study also noted reports of a multisystem inflammatory syndrome in children infected with COVID-19, which has led to severe illness and death in some cases.
“The subpopulations of children at risk and the full spectrum of multisystem inflammatory syndrome in children remain unknown,” the study’s authors wrote.
"However, the low attack rate among children in the youngest age group suggested that they “are less likely to become infected than adults and may not be drivers of the epidemic," they added.
“The low attack rate suggests that strict compliance with infection control may be able to eliminate or reduce the risk of transmission from adults to children in household settings."
ABOUT 4 IN 10 CHILDREN ASYMPTOMATIC
Another recent study by KKH of 39 children with COVID-19 in Singapore found that 38.5 per cent of the children remained asymptomatic.
This high proportion of asymptomatic cases made it difficult to identify children with COVID-19 based on symptomatic testing alone, said author Dr Li Jiahui.
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“This important finding underscores the importance of early screening and isolation of children upon detection of potential exposure to an index case of COVID-19,” added Dr Yung, also a co-author of the study.
The study was published in August in the Annals, the official medical journal of the Academy of Medicine, Singapore.
It drew on data from 39 cases of children with COVID-19 who were admitted to KKH between January and May. This represented about 70 per cent of all pediatric cases detected in Singapore.
A low-grade fever, runny nose, sore throat and cough were the most common symptoms reported by children with COVID-19, according to the study. Other symptoms included diarrhoea and loss of smell or taste.
“Symptomatic children were more likely to have abnormal laboratory parameters but they did not have a poorer outcome compared to asymptomatic cases,” the study found.
All the children had a “mild course of illness” and were discharged “well”, with a mean hospital stay of 15 days, according to the study.