Preliminary results from a study underway in Montreal shed important light on the extent to which 2 to 17 years-old have had COVID-19 between last October 2020 and this April 2021. As an overall average, 5.8% of participating children were found to have antibodies to SARS-CoV-2, the virus that causes COVID-19. However, the seroprevalence (proportion of children with antibodies in their blood) increased sharply over time. In October and November of 2020, only 3.3% of children had antibodies. By April 2021, in the third wave, 8.9% of the students tested had antibodies. The results of this study are preliminary and have not yet been peer-reviewed.

The study which was announced October 20, 2020, named EnCORE, collected finger prick (dried blood spot) samples from 1,632 children and adolescents attending schools and daycares in four neighbourhoods of Montreal: the West Island, Plateau Mont-Royal, Montreal North, and Mercier-Hochelaga Maisonneuve (HOMA).

“Our preliminary results show infections in children and adolescents grew faster in the February-April 2021 period,” says project lead Dr. Kate Zinszer, Assistant Professor at l’École de santé publique, Université de Montréal, and researcher at the Centre de recherche en santé publique. “The results also suggest that seroprevalence is higher in neighbourhoods with lower socio-economic indexes and at a greater percentage for racialized residents. That said, our results could also simply reflect the later timing of recruitment this winter and spring in the Hochelaga-Maisonneuve (HOMA) and Montreal-North areas, corresponding to increased transmission via variants during our third wave.”

Seroprevalence estimates by neighbourhood suggest that 4.8% of children and teens on the West Island had antibodies to SARS-CoV-2, 5.4% in the Plateau, 6.2% in HOMA, and 7.3% in Montreal-North. The blood samples were taken from 354 children in daycare, 725 children in elementary schools, and 553 students in high schools. Looking at the geographical split, 33% were from Plateau-Mont-Royal, 31% from the West Island, 22% from HOMA, and 15% from Montreal-North.

“Interestingly, of the 95 children who tested positive for antibodies with our serology test, 82% had previously tested negative for SARS-CoV-2 or had never been tested for the virus. This means most of the participating children’s infections would have gone undetected without this study,” adds Dr. Zinszer.

The survey portion of the study also gives insight into vaccine confidence and the mental health repercussions of the pandemic on Montreal children, teens and their parents.

“Most of the parents surveyed, 86%, said that they were likely to have their child vaccinated against COVID-19, but the percent is lower among visible minorities,” states Dr. Zinszer. “About a third (33%) of parents who were from visible minorities indicated they would be reticent to vaccinate their children.”

When it comes to behaviour and emotional health, surveys filled out by parents suggest 33% of children have had difficulties with emotions, concentration, behaviour, or relationships with other people. In addition, 55% of children have been less physically active, 54% have been spending more time on screens for non-educational purposes, 81% have been spending less in-person time with friends, and 54% are less socially connected. Interestingly, 14% of parents reported their child was more socially connected during the pandemic than she or he had been before COVID hit.

“These preliminary results correspond with growing evidence that COVID-19 is affecting poorer neighbourhoods and racialized communities more than others,” says CITF Leadership Group member Dr. Jim Kellner, a pediatric infectious disease consultant and leader of the CITF’s Pediatric Network. “This means that efforts to protect these communities through public health surveillance, safer workplaces, and tailored vaccine distribution need to be scaled up urgently. As well, vaccinating adolescents is the right thing to do, now that we have vaccines that are Health Canada approved for age 12 and up. Although seroprevalence may have reached 9.6% in some neighbourhoods recently, herd immunity is far off. We need to include younger children in vaccination strategies, offering them safe and effective protection from this very serious illness.”

Recruitment continues

The EnCORE research study is starting its second phase and is calling on all parents and legal guardians with children attending selected schools and daycares to have their children take part. Participation requires a consent form, an online questionnaire, and a home finger prick test. Researchers will inform parents if their child does have antibodies to SARS-CoV-2, although that still does not guarantee immunity against the virus that causes COVID-19. Vaccination is recommended in any case for people who have antibodies to SARS-CoV-2. To participate in the study or see if your child’s school or daycare is participating, please visit the EnCORE website:

About the COVID-19 Immunity Task Force

The Government of Canada established the COVID-19 Immunity Task Force in late April 2020. The Task Force is overseen by a Leadership Group of volunteers that includes leading Canadian scientists and experts from universities and healthcare homes across Canada who are focused on understanding the nature of immunity arising from the novel coronavirus that causes COVID-19. To that end, the CITF is supporting numerous studies to determine the extent of SARS-CoV-2 infection in Canada (in the general population as well as in specific communities and priority populations), understand the nature of immunity following infection, develop improved antibody testing methods, and help monitor the effectiveness and safety of vaccines as they are rolled out across Canada. The Task Force and its Secretariat accordingly work closely with a range of partners, including governments, public health agencies, institutions, health organizations, research teams, other task forces, and engages communities and stakeholders. Most recently, the Task Force has been asked to support vaccine surveillance, effectiveness and safety as part of its overall objective to generate data and ideas that inform interventions aimed at slowing—and ultimately stopping—the spread of SARS-CoV-2 in Canada. For more information visit:


COVID-19 Immunity Task Force
Rebecca Burns
Cell: +1.438.871.8763
Caroline Phaneuf
Cell: +1.514.444.4532