This is a summary, written by members of the CITF Secretariat.
See an infographic of the preliminary Round 3 results.
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

The latest, preliminary, non-peer reviewed results from the EnCORE study (Round Three) show an increasing number of Montreal youth, aged 2 to 17, acquired antibodies due to a SARS-CoV-2 infection between October 2020 and December 2021. Its data found that 10.6% of participants had antibodies to SARS-CoV-2 between November and December 2021, whereas 9.7% had antibodies between May and August 2021 and 5.8% between October 2020 and March 2021. It’s important to note that 82% of participants’ samples were collected before the Omicron variant became widespread in the Montreal region. CITF-funded researcher Dr. Kate Zinszer, from the Université de Montréal, is the project lead.

Key Results:

  • Those with the highest rate of infection-acquired seroprevalence over time were children between the ages of 5 and 11, with 13.2% seroprevalence recorded November 2021-December 2021. This was followed by 12- to 17-year-olds (8.7%) and 2- to 4-year-olds (6.8%).
  • Seroreversion, when a child tests positive for antibodies to SARS-CoV-2 and later tests negative, helps us understand how long antibodies remain detectable. In this sample, 59% of previously positive participants were still positive after 6 months, yet after 1 year only 15% of previously positive participants had detectable antibodies.
  • Seroprevalence varied between the four neighbourhoods involved in the study, with Montreal North reporting 16.7% seroprevalence, Mercier-Hochelaga-Maisonneuve (HOMA) 16.7%, Plateau Mont-Royal 12.6%, and the West Island reporting 3.2% seroprevalence.
  • The parents of 81% of the participants reported their children aged 5 and older had received at least 1 dose of the vaccine.
  • The rate of seroconversion, when a child becomes positive for SARS-CoV-2, was estimated to be approximately 12/100, meaning that if 100 children are followed over 1 year, we would expect 12 of them to test positive for SARS-CoV-2.
  • Compared with the time before the COVID-19 pandemic:
    • 31% of participants reported less time on physical activity
    • 47% spent less time with friends in-person
  • At the time of the survey:
    • 45% of parents reported being concerned about their child’s mental health;
    • 36% of parents reported their children experiencing difficulties with emotions, concentration, behaviour or relationships;
    • 42% of parents reported that their children spent more time on screen for non-educational purposes.
  • Among adolescents (14-17 years old) in the study, 99% had received at least one dose of vaccine. The top reasons adolescents chose to get vaccinated were: to protect themselves; to protect their family; to stop the spread of the virus.

The 872 participants were recruited from schools and daycares in four areas of Montreal with distinct socioeconomic and population differences.