More than one-third of kids with COVID-19 show no symptoms, says study

More than one-third of kids infected with the novel coronavirus are asymptomatic, according to a study which confirms that children diagnosed with COVID-19 may represent just a fraction of those infected.

The research, published in the journal CMAJ, analysed results for 2,463 children in Alberta, Canada, who were tested during the first wave of the pandemic -- March to September -- for COVID-19 infection.

"The concern from a public health perspective is that there is probably a lot of COVID-19 circulating in the community that people don't even realise," said Finlay McAlister, a co-author of the study from the University of Alberta Faculty of Medicine and Dentistry in Canada.

"When we see reports of 1,200 new cases per day in the province of Alberta, that's likely just the tip of the iceberg -- there are likely many people who don't know they have the disease and are potentially spreading it," he said.

Of the 2,463 children, 1,987 had a positive test result for COVID-19 and 476 had a negative result, and of those who tested positive, 714 -- about 36 per cent --reported being asymptomatic.

Due to the asymptomatic nature of the disease in up to one-third of children, McAlister said closing schools for a longer period over Christmas was the right decision.

"As far as we know, kids are less likely to spread disease than adults, but the risk is not zero. Presumably asymptomatic spreaders are less contagious than the person sitting nearby who is sneezing all over you, but we don't know that for sure," he added.

The researchers also found that cough, runny nose and sore throat were three of the most common symptoms among children with COVID-19 infection -- showing up in 25, 19 and 16 per cent of cases respectively.

However, they said these symptoms were slightly more common among those with negative COVID-19 test results, and therefore not predictive of a positive test.

"Of course, kids are at risk of contracting many different viruses, so the COVID-specific symptoms are actually more things like loss of taste and smell, headache, fever, and nausea and vomiting, not runny nose, a cough and sore throat," McAlister said.

"Some people with COVID feel well and don't realise they have it so they socialise with friends and unintentionally spread the virus, and I think that's the big issue," he added.