Table 5. Joint rapid qualitative risk assessment on severe acute respiratory syndrome coronavirus 2-associated risk for mink farms in British Columbia, June 29, 2021.

Methods
The scope of the assessment was limited to the mink farms in the Fraser Health Authority and British Columbia. The outcome of interest was the circulation of a mink-induced SARS-CoV-2 variant of interest (VOI) in the community that could potentially increase transmission, cause more severe disease in humans, escape vaccines or significantly decrease the effectiveness of therapeutic and diagnostic technologies, compared with what is seen with currently circulating variants. The pathways assessed were human-mink-human and human-mink-wildlife-human. Two timeframes were assessed: 1) short term: completion of the current production cycle, up to before the start of the next breeding season; and 2) long term: the next five years. A multi-jurisdictional expert group jointly completed all steps of the process. Using a modified Delphi approach, the expert group assessed probability, impact, and uncertainty estimates. Probabilities along the scenario pathways were combined as per accepted qualitative risk assessment methodologies. Several assumptions were made by the expert group that influence the results. There is often a high degree of uncertainty related to the assumptions. They are important to highlight because changes to the assumptions may affect the final estimates, and significant changes may indicate the need for reassessment.
Probability level, impact and uncertainties
The combined assessment of probability and the assessment of consequence the emergence and circulation of a VOI in the community of mink/wildlife origin were as follows: 1. What is the likelihood and impact of emergence and circulation of a SARS-CoV-2 VOI in the community due to virus evolution in mink or “wildlife after exposure to mink” during completion of this cycle, compared to what is seen with currently circulating variants and evolving public health measures? Probability: very unlikely (VOI in wildlife pathway) to very unlikely/unlikely (VOI in mink pathway) Uncertainty: moderate (VOI in mink pathway) to high (VOI in wildlife pathway) Impact: minor to moderate at the local/regional level, and slightly less at the provincial level Uncertainty: moderate to high 2. What is the likelihood and impact of emergence and circulation of a SARS-CoV-2 VOI in the community due to virus evolution in mink or “wildlife after exposure to mink” WITHIN THE NEXT FIVE YEARS, compared to what is seen with currently circulating variants and evolving public health measures? Probability: very unlikely (VOI in wildlife pathway) to unlikely (VOI in mink pathway) Uncertainty: moderate (VOI in mink pathway) to high (VOI in wildlife pathway) Impact: minor to moderate at the local/regional level, and slightly less at the provincial level Uncertainty: moderate to high The combined probability estimates for both timeframes of the human-mink-human pathway were driven primarily by the probability of the evolution of the virus into a VOI in a mink herd, with higher uncertainty associated with the probability in the five-year assessment due to the higher uncertainty in the expected number of mink herd outbreaks per year as time goes on and higher uncertainty regarding the evolution of a VOI. The risk assessment for the next five years assumed limited control measures. In the pathway involving wildlife, most steps were estimated as less probable than for the direct pathway from mink-to-humans, with a similar level of uncertainty. The mode of the overall probability for the human-mink-wildlife-human pathway during both periods was very low, regardless of the spread scenario in wildlife (limited spread or reservoir). These estimates were driven primarily by 1): the probability of evolution of the virus into a VOI in wildlife that was assessed as very unlikely to occur and 2) the probability that a person would contract the virus from wildlife was assessed as very unlikely. Experts expressed it is more likely that a VOI will arise in humans rather than in mink. If there was emergence and circulation of a VOI in the community that was of mink/wildlife origin, the magnitude of the impact on the health of the population above the current/ongoing pandemic impacts for this cycle were estimated as likely to be minor to moderate at the local/regional level, and slightly less at the provincial level. The uncertainty associated with this was moderate to high. The magnitude of the impact at the five-year timeframe was assessed as likely to be similar, with a higher level of uncertainty.

Abbreviations: SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; VOI, variant of interest