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SINGAPORE: Children under the age of five have the “lowest risk” of contracting COVID-19 from adults, according to a Singapore study on household transmission of the virus.
The KK Women’s and Children’s Hospital (KKH) study was based on data from children who were household contacts of COVID-19 cases and were screened for the disease in the hospital between March and April.
A total of 213 children under the age of 16 were tested for COVID-19 during this period. They come from 137 households with a total of 223 adults who were confirmed cases, according to the study.
Of the 213 children tested, 13 cases of adult-to-child transmission of COVID-19 were detected in seven households.
This equaled a 6.1 percent “attack rate” among children and 5.2 percent of 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%.
This was the lowest rate among all age groups, compared to 8.1% for children ages five to nine and 9.8% for children ages 10 to 16.
The findings were published in October in the Journal of Pediatrics.
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The study also found that the risk of secondary infection in children was higher if the COVID-19 index patient was the child’s mother. At 11.1 percent, the rate was almost double that if the index case was a parent or grandparent.
“Because the population’s 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 study authors wrote.
“Since transmission is known to be correlated with the degree of contact, one might expect attack rates to be higher in younger children, who presumably have closer interactions with their parents than older children.
“However, in our study, the attack rate was lower in the younger age group,” the study authors wrote.
Dr. Yung Chee Fu, a consultant for the KKH Infectious Diseases Service and a co-author of the study, said that younger children may be more resistant to COVID-19 infection.
“It is possible that younger children are more resistant to SARS-CoV-2 infection at the cellular level,” he said in an Oct. 13 newsletter about the study on the KKH website.
Dr. Yung referred to studies that have found a trend of “higher expression”, with increasing age, of an enzyme receptor in the nasal epithelium that is used by the coronavirus for host entry.
The study also looked at reports of a multisystem inflammatory syndrome in children infected with COVID-19, which has led to severe illness and death in some cases.
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“The subpopulations of children at risk and the full spectrum of multisystem inflammatory syndrome in children remain unknown,” the study authors wrote.
“However, the low attack rate among children in the youngest age group suggests that” they are less likely to become infected than adults and may not be the drivers of the epidemic, “they added.
“The low attack rate suggests that strict adherence to infection control can eliminate or reduce the risk of transmission from adults to children at home.”
About 4 in 10 asymptomatic children
Another recent KKH study of 39 children with COVID-19 in Singapore found that 38.5 percent of the children remained asymptomatic.
This high proportion of asymptomatic cases made it difficult to identify children with COVID-19 based solely on symptomatic tests, said author Dr. Li Jiahui.
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“This important finding underscores the importance of early detection and isolation of children following detection of possible 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 Annals, the official medical journal of the Singapore Academy of Medicine.
It was based on data from 39 cases of children with COVID-19 who were admitted to KKH between January and May. This accounted for around 70 percent of all pediatric cases detected in Singapore.
Mild 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 diarrhea and loss of smell or taste.
“Symptomatic children were more likely to have abnormal laboratory parameters, but they did not have a worse outcome compared to asymptomatic cases,” the study found.
All the children had a “mild course of the disease” and were discharged “well,” with a mean hospital stay of 15 days, according to the study.
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