Study registration: *
Publication Nasreen S, medRxiv, 2021
Dates: 2020-12-14 to 2021-08-03
Funding: Public/non profit (Canadian Immunization Research Network (CIRN) through a grant from the Public Health Agency of Canada and the Canadian Institutes of Health Research (CNF 151944). Public Health Agency of Canada, through the Vaccine Surveillance Reference group and the COVID-19 Immunity Task Force. ICES, which is funded by an annual grant from the Ontario Ministry of Health (MOH).)
Conflict of interest: Yes (KW is CEO of CANImmunize and serves on the data safety board for the Medicago COVID-19 vaccine trial.)

Methods

Study design:Test-negative
Description of participants: Symptomatic community-dwelling individuals aged ≥16 years with no history of SARS-CoV-2 infection in Canada
Inclusion criteria:
  • Community-dwelling individuals
  • aged ≥16 years
  • had symptoms consistent with or a severe outcome attributable to COVID-19
  • tested for SARS- CoV-2 between 14 December 2020 and 3 August 2021.

Exclusion criteria:
  • Individuals who tested positive for SARS-CoV-2 prior to their selected index date and those who received Ad26.COV2.S (Janssen), because it has not been used in Ontario (despite receiving approval), or mixed (ChAdOx1-mRNA or different mRNA) vaccine schedules.

Follow-up duration (months): 7.5
Vaccines:
  • 1 or 2 doses of mRNA-1273
  • 1 or 2 doses of ChAdOx1-S
  • 1 or 2 doses of BNT162b2
Variant description :
Variant name: Delta
Evidence: Indirect evidence (prevalence of variant in the population: 1 to 40%)
Documents
available

Protocol

NR

Statistical plan

NR

Data-sharing stated: Yes, the full dataset creation plan and underlying analytic code are available from the authors upon request
Data accessibility: www.ices.on.ca/DAS (email: das@ices.on.ca)
General comment Control for confounding was good but uncontrolled confounding cannot be ruled out; in addition there is a possibility of selection bias (particularly for the outcome severe disease), including due to uncertainties over the validity of a test-negative design in this regard.