COVID-19: Variant risk assessment methods

Published: January 27, 2023

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• Variant risk assessment framework
• Criteria for estimating the level of uncertainty

Variant risk assessment framework

The table below has been adapted from the Public Health England Risk Assessment Framework (PDF) for SARS-CoV-2 variants of concern and variants under investigation to determine the level of risk posed by the variant. It will serve as a guidance when determining the comparative risk level to the reference variant.

Table 1. Risk comparison relative to baseline or specific reference variant (e.g., Omicron BA.2)

Indicator	Reduced risk	Comparable risk	Elevated risk
Transmissibility	Limited person-to-person transmission.	Similar transmissibility to baseline or specific reference variant.	More transmissible than baseline or specific reference variant.
Disease severity	Evidence of less severe clinical picture (asymptomatic or symptomatic) compared with baseline or specific reference variant.	Similar clinical picture in terms of hospitalization rates and/or case fatality compared with baseline or specific reference variant, or experimental animal data suggesting potential for increased disease severity in humans.	More severe clinical picture (hospitalization rates) or higher case fatality compared with baseline or specific reference variant.
Immune evasionTable 1 Footnote 1: Immunity after infection	Evidence of no infection in humans previously infected with the baseline variant, and/or limited reinfection cases found in humans previously infected with any variant, or structural data suggesting no antigenic differences.	Evidence of limited infection in humans with known prior infection, or evidence of limited functional evasion of immunity after infection, or structural data suggesting some antigenic differences.	Evidence of frequent infection in humans with known prior infection, or evidence of marked functional evasion of immunity after infection, or structural data suggesting significant antigenic differences.
Immune evasionTable 1 Footnote 1: Immunity after vaccination	Evidence that vaccine performance is preserved, or structural data suggesting no antigenic difference in vaccine target epitopes.	Evidence of limited functional evasion of vaccine derived immunity, or structural data suggesting some differences in vaccine target epitopes.	Evidence of marked functional evasion of vaccine derived immunity, or structural data suggesting significant differences in vaccine target epitopes.
Treatments	Evidence of increased clinical effectiveness of therapeuticsTable 1 Footnote 2 or increased number of effective therapeuticsTable 1 Footnote 2 or evidence of increased in vitro activityTable 1 Footnote 3 of a therapeutic.	Evidence of comparable clinical effectiveness of therapeuticsTable 1 Footnote 2 or no change in the number of effective therapeuticsTable 1 Footnote 2 or evidence of retained in vitro activity creased in vitro activityTable 1 Footnote 3 of therapeutics.	Evidence of decreased clinical effectiveness of therapeuticsTable 1 Footnote 2 or decrease in the number of effective therapeuticsTable 1 Footnote 2 or evidence of reduced in vitro activity or loss of in vitro activity creased in vitro activityTable 1 Footnote 3 of therapeutics.
Table 1 - Footnote 1 Immune evasion is based on two indicators: immunity after infection and/or immunity after vaccination. Return to Table 1 Footnote 1 referrer Table 1 - Footnote 2 Therapeutic: Refers to a therapeutic procured and available in Canada. Return to Table 1 Footnote 2 referrer Table 1 - Footnote 3 Activity: Refers to a variant's in vitro fold change in activity for therapeutics reported by the OpenData Portal: SARS-CoV-2 variants and therapeutics. It is not known how in vitro data correlate with clinical outcomes. Return to Table 1 Footnote 3 referrer

Criteria for estimating the level of uncertainty

Very high uncertainty: Criteria is lack of data or reliable information; results are based on crude speculation only.

High uncertainty: Criteria is limited data or reliable information available; results are based on educated guess.

Moderate uncertainty: Criteria is some gaps in availability or reliability of data and information, or conflicting data; results based on limited consensus.

Low uncertainty: Criteria is reliable data and information available but may be limited in quantity, or be variable; results based on expert consensus.

Very low uncertainty: Criteria is reliable data and information are available in sufficient quantity; results strongly anchored in empiric data or concrete information.