Children and youth had highest rates of COVID before third wave

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When researchers asked thousands of Canadians to submit blood samples for SARS-CoV-2 antibody testing, they discovered something surprising — children and youth, not older people, had the highest rates of COVID-19 infections in the country.

The Statistics Canada research, which was completed before the third wave of the pandemic began in the spring, is the most representative study to date of the number of Canadians who had developed antibodies from past infections.

The numbers were small. Just 2.6 per cent of people studied had antibodies showing that they had been infected. But, while children have represented a very small proportion of serious COVID-19 illnesses and hospitalizations since the pandemic began, the research shows Canadians 19 and younger were more likely to become infected than adults, although they were often not aware of it. In about one-third of cases, those infections were asymptomatic.

Researchers also found that visible minorities, young and old, were more than twice as likely to have had past infections leading up to the third wave compared to other Canadians. Public health units in Ottawa and elsewhere have noted similar trends. Researchers received samples from more than 11,000 Canadians age one and older. Long-term care and retirement home residents were not included.

The research, released Wednesday, comes as millions of Canadian children under 12, who do not yet qualify for COVID vaccines, will soon head back to school. In Ontario, parents, health officials and others have been calling for a detailed plan from the provincial government that will ensure they get back into class, but safely. Children in Ontario had the fewest in-person school days in the country last year.

Dr. Paul Roumeliotis, the medical officer of health for the Eastern Ontario Health Unit and a pediatrician, is among those who have been advising provincial officials on a safe return to school.

He said he was not surprised to see the research showing children and youth had higher infection rates leading up to the third wave. He too saw an increase in positive tests among those age groups at the beginning of 2021, while children were out of school.

Roumeliotis said plans are under way to ensure return to school is safe, including upgrades to ventilation and air filters. He said children under 12 will have several levels of protection — not only masks and distancing, but having those around them, including teachers, family members and older children, fully vaccinated. Older students should be vaccinated by the time school starts.

“Vaccines add that extra layer of protection,” he said.

Roumeliotis said he is confident that children will be able to have “a more normal school entry than last year” as a result.

He was among those calling for schools to reopen in June.

In coming weeks, he said, there should be more focus on increasing vaccination levels among youths and young adults, who lag behind older adults.

Epidemiologist Catherine Hankins who co-chairs the federal COVID Immunity Task Force that funded the antibody research, said she was surprised people over 60 who participated had the lowest rates of antibodies due to infection. Just 1.4 per cent of people 60 and over who participated in the study had antibodies indicating they had prior infections, compared to 3.3 per cent of children and youth 19 and younger. Among adults from 20 to 59, the rate was 2.9 per cent. At the time the research was done just one per cent of those studied had antibodies from vaccination. No children and youth had been vaccinated.

Among other things, Hankins said the research shows that Canadians were vulnerable when the third wave, fuelled by the highly transmissible Alpha variant, hit in the spring. Vaccination levels were low and few Canadians had antibodies due to previous infection.

“We were not well prepared for the third wave,” she said.

She too said it is important that all the adults around children are vaccinated. It is unlikely a vaccine will be approved for children under 12 until late fall. And then, she said, there is the question of whether Canada should be vaccinating young children who seldom get seriously ill, or contemplating boosters, when much of the world remains unvaccinated.

The Canadians who participated in the study received a test kit in the mail so they could give blood samples from home by pricking their fingers.

Albertans had the highest rates of antibodies due to previous infections — four per cent — followed by Quebec, at 3.2 per cent, Saskatchewan at 2.9 per cent and Ontario at 2.5 per cent. The Atlantic provinces had only 0.5 per cent seroprevalence due to past infection and the numbers were too low to produce a statistical estimate in the territories. The data was collected between November 2020 and April 2021.