A study conducted by researchers in Belgium has found no evidence to support concerns that asymptomatic young children may be a source of severe acute respiratory syndrome coronavirus disease 2 (SARS-CoV-2) transmission.
No cases of asymptomatic carriers were detected among a cohort of 84 children (aged six to 30 months) attending daycare centers across Belgium shortly following the 29th February outbreak in the country and before the lockdown was implemented on 18th March.
A pre-print version of the article can be accessed on the server medRxiv*, while the paper undergoes peer review.
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Older adults more likely to experience severe disease
Since the outbreak of SARS-CoV-2 in Wuhan, China in December 2019, the virus has swept the globe and been declared a pandemic emergency by the World Health Organization (WHO) on 20th March.
The primary modes of transmission between people are close contact with an infected individual and contact with contaminated objects. Symptoms, which vary in severity, include dry cough, fever, shortness of breath, difficulty breathing, and respiratory failure.
Research has shown that older people are the most likely to experience severe symptoms of the associated coronavirus disease 2019 (COVID-19). Still, less is known about the severity of disease and transmission rates among young children and infants.
Concerns about asymptomatic young children
Some research conducted in China suggests that symptoms are less severe among children and more likely to go unrecognized compared with adults.
Potential explanations include less likelihood of exposure to pathogens and infected people; lower levels of the angiotensin-converting enzyme 2 (ACE 2) receptor for SARS-CoV-2; a higher rate of respiratory infection during the winter meaning a higher antibody level, and a less developed immune system causing children to react differently to pathogens.
The authors of the current study say that “the lower symptomatic disease incidence in the pediatric population raises the concern that this population could be an important source of SARS-CoV-2 transmission.”
The situation in Belgium
In Belgium, the SARS-CoV-2 epidemic started on 29th February, and 689 cases had been confirmed across the country by 13th March.
Understanding the role children may play in the transmission is vital for deciding on the public health measures that should be implemented and on potential strategies for exiting from the lockdown currently imposed.
To investigate, Heidi Theeten (Vaccine and Infectious Disease Institute, University of Antwerp) and colleagues analyzed nasopharyngeal swabs taken from 84 children (aged six to 30 months) attending eight daycare centers in Belgium (four in Flanders, three in Wallonia and one in Brussels) during the first weeks (2nd to 12th March) of the epidemic.
Around one-half of the children were girls, about half had signs of the common cold, just over half shared their household with at least one sibling, and the majority attended daycare at least twice a week and had non-smoking parents.
“No asymptomatic carriage of SARS-CoV-2 was detected”
The team reports that all of the children tested did not have SARS-CoV-2, meaning that shortly following the start of the epidemic and before the lockdown was implemented on 18th March, there was no asymptomatic carriage detected in this random sample of 84 young children in daycare.
Theeten and colleagues say the findings are in line with those of other studies suggesting that children only play a minimal role in the SARS-COV-2 epidemic.
A large-scale screening study conducted in Iceland reported that children aged under 10 years were less likely to test positive than children aged 10 years or more. Another large-scale survey conducted in Italy found no positive cases among children aged under 10 years, either before or after lockdown had been implemented in the district where the first death had occurred.
A household study conducted in China found that the rate of secondary cases among children was only 4%, compared with 17% among adults.
In addition, since the outbreak began, only a handful of deaths worldwide have involved children, who generally only experience mild symptoms.
What does this study add?
“Our study adds that in Belgium, where the epidemic was imported mainly by adult travelers, there is no sign of early introduction into daycare centers at the moment children were not yet isolated at home although the virus was clearly circulating,” write Theeten and colleagues.
“It is clear that more evidence is needed to understand the actual role of young children in the transmission of SARS-CoV-2 and their infection risk when attending daycare,” they conclude.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.