More than one-third of children with COVID-19 show no symptoms: study

"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 realize," said Finlay McAlister, a professor of medicine in the Faculty of Medicine & Dentistry.

"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.

For the study, McAlister's team analyzed results for 2,463 children who were tested during the first wave of the pandemic -- March to September -- for COVID-19 infection.

All told, 1,987 children had a positive test result for COVID-19 and 476 had a negative result. Of children who tested positive, 714 -- 35.9 per cent -- reported being asymptomatic.

"It speaks to the school safety programs," he said. "We can do all the COVID-19 questionnaires we want, but if one-third of the kids are asymptomatic, the answer is going to be no to all the questions -- yet they're still infected."

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

"As far as we know, kids are less likely to spread disease than adults, but the risk is not zero," he said. "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."

The researchers also found that although 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 -- they were actually 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," he said.

McAlister noted that his group has a similar paper coming out that shows sore throats and runny noses aren't reliable signs of COVID-19 in adults either, although the vast majority of adults (84 per cent) do show symptoms.

"Sore throat and runny nose means you've got some kind of upper respiratory tract infection, but fever, headache, and loss of taste or smell are the big ones for indicating that one may have COVID-19 rather than another viral upper respiratory tract infection," he said, adding nausea and vomiting wasn't as prominent in adults.

McAlister added that if people have any symptoms at all, they should stay home and get tested, while even those who feel well should still be doing everything they can to stay safe -- wearing a protective mask, frequent handwashing, keeping distance, and avoiding meeting indoors.

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