A team of researchers analyzed all of the nearly 220,000 positive cases in Ontario during the pandemic, from January 2020 to January 2021.
The data shows that 35 per cent of children under the age of nine who tested positive for the virus were asymptomatic.
Another 31.4 per cent only showed a single symptom with the most common being a fever.
Engineering professor Dr. Ed McBean led the study and said the data is “worrisome” and could cause a rapid spread of COVID-19 transmission in communities.
“Our findings indicate that asymptomatic and pre-symptomatic cases are substantial in number,” McBean said. “This highlights the importance of targeting asymptomatic and mild infections in the continuing effort to control the spread of COVID-19.”
Overall cases were milder in children and very few showed signs of a cough — a frequent symptom in adults over the age of 40, the university said.
The study has been recently published in Infectious Disease Reports and used data obtained from the Ministry of Health.
It consisted of over 219,075 individual cases that tested positive from over 8.4 million COVID-19 tests performed throughout Ontario prior to Jan. 10, 2021.
The positive tests were classified by symptoms including cough, fatigue, fever, headache, shortness of breath, sore throat and no symptoms.
“There is a broad range of severity of illnesses from COVID-19 making asymptomatic infections important to understand because the virus can still be transmitted, causing critical illness in others,” McBean said.
Even with schools closed and a provincewide stay-at-home order in place, McBean believes there is still a need to focus on asymptomatic testing.
“Given the fact that more than 30 per cent of children with the virus are asymptomatic, it would be effective to invest in testing to identify asymptomatic children in situations where children are not wearing masks, such as in daycares, and are in close proximity to other children or adults, such as multi-generational homes and daycares,” he said.
The Ontario government first launched voluntary targeted testing for students and staff last fall in hot spots such as Toronto, Peel and York.
That approach was expanded in February and as of April 16, over 3,000 schools have been invited for asymptomatic testing.
According to Education Minister Stephen Lecce’s office, about 48,700 tests have been completed, of which 317 confirmed cases were identified.
“Our government has taken action to deploy asymptomatic testing provincewide, the first program of its kind in Canada, and testing results continue to demonstrate a low positivity rate,” spokesperson Caitlin Clark said in an email.
“We will continue to promote and encourage all students staff and families to take advantage of this program – which uses the least invasive testing options possible.”