Vast majority of Montreal-area teens developed COVID-19 antibodies, study shows

Five- to 11-year-olds showed the highest rate of antibodies to protein N, suggesting they developed them after catching COVID-19. Teens had the highest rate of antibodies associated with vaccines.

Researchers studied 641 blood samples from babies, children and teens

Noa Mendell, 14, receives a COVID-19 vaccine shot from Laurence Dubé at a COVID-19 vaccination site in Montreal, Saturday, May 22, 2021. (Graham Hughes/The Canadian Press)

Nearly all Montreal-area teenagers age 12 to 17 have developed COVID-19 antibodies, according to a CHU Sainte-Justine study.

The study, led by pediatric infectious diseases specialist Dr. Caroline Quach, shows the highest level of antibodies — 97 per cent — is in teens age 12 to 17, when taking into account those who developed antibodies through either vaccination or natural infection.

"It gives us enough information to tell us there have been a lot of infections and recently, in all likelihood, Omicron [infections]," Quebec's interim public health director, Dr. Luc Boileau, who commissioned the study, said at a news conference Wednesday.

Omicron has been the dominant COVID-19 variant in the province since December 2021, Quebec's Health Ministry confirms.

Data from Quebec's institute of public health (INSPQ) published Wednesday shows nearly three million Quebecers have been infected with Omicron.

From Jan. 26 to Feb. 10, researchers assessed the proportion of children under 18 with an antibody response to COVID-19.

They used blood samples from 641 young patients at the CHU Sainte-Justine emergency rooms.

Once their blood had been tested for whatever had brought them to the ER, the leftover blood was tested for COVID antibodies. Then, the samples, which were made anonymous, were sent to Héma-Québec's laboratory for evaluation.

From Jan. 26 to Feb. 10, researchers assessed the proportion of children under 18 with an antibody response to COVID-19. Protein N, in pink, indicates antibodies that come from exposure to COVID. (CHU Sainte-Justine)

A person vaccinated against COVID-19 develops only one kind of antibodies to the virus, to the spike (S) protein. Someone who develops antibodies after being infected develops two types — the nucleocapsid protein (N) and the S protein, according to Quach.

"With time, you tend to lose your antibodies to protein N much faster than you would lose the S," she said.

Five- to 11-year-olds showed the highest rate of antibodies to protein N (43 per cent), suggesting they developed them after catching COVID-19.

The antibody against protein N was found among nearly 30 per cent of children between six months to four years old, meaning they had caught COVID-19. Children under the age of four are not eligible for vaccination at this time.

The results show that nearly 30 per cent of infants under the age of six months had had COVID-19 or their mothers had caught it and transferred maternal antibodies to them.

Over the hump

The findings come as hospitalizations in the province are expected to decline and Quebec prepares to lift pandemic health measures in schools.

Elementary and high school students will no longer have to wear masks in class when they return from March break, on March 7 or 14, depending on the region.

Given Omicron has already spread so quickly, Quach said lifting the mask requirement in schools is a fair public health recommendation.

"These children were already eating all together at lunch. They were already spending half an hour to an hour everyday without masks," she said. "Because of the contagiousness of Omicron, that's enough to contaminate whoever needs to be contaminated in the classroom."

"We passed the hump of the Omicron wave, which doesn't mean that everything will be hunky dory from now on but I think that we should be seeing a decrease in mortality and cases," she said.

Quach says the study will continue until 1,000 samples are collected, which she expects will happen in the next two weeks.

with files from Matt D'Amours