Table 2. Sequential interventions to manage and mitigate risk from severe acute respiratory syndrome coronavirus 2 on mink farms in British Columbia, October 2020 to October 2021.

Trigger	Purpose and considerations/actions	Outcomes and challenges
1. OHC, formed in October 2020
Large outbreaks reported in mink farms in European countries	Purpose: To assess, mitigate, and respond to risks from SARS-CoV-2 on BC mink farms using a One Health approach. Action: The OHC held weekly to semi-weekly meetings to: share information and contextualized technical and on-the-ground expertise of all members; coordinate human, animal, and environmental surveillance strategies; jointly identify biosafety gaps to be addressed and request for funds or other response tools; collaborate on decision-making based on shared situational assessments and evidence review; coordinate communication with mink farm operators; and liaise with other jurisdictions and organizations such as the Public Health Agency of Canada, United States Centers for Disease Control and Prevention and the World Health Organization.	The OHC enabled timely and effective response to mink farm outbreaks, realistic and implementable regulations, policies and guidelines, and optimization and sharing of technical, financial and human resources. The OHC also helped to provide unified and coordinated messaging to mink farm operators. Challenges in differing perceptions of risk or related decisions were typically surmountable and consensus was possible to reach in most areas. In some circumstances where specific legal jurisdiction clearly identified the most responsible organization, decisions were left to that organization.
2. Mink farm inspections, starting December 4, 2020
2.1 Initial inspections at Farm 1
Outbreak investigation at Farm 1	Purpose: To assess adherence to enhanced biosafety measures and identify gaps for improvement. Action: Coordinated inspections were carried out by OHC partners (i.e. PH, MAFF, and/or WorkSafeBC).	Inspections at Farm 1 found limited biosafety measure implementation. Out of concern for workers potentially contracting a mink-adapted COVID-19 variant, only activities necessary for animal welfare were immediately allowed to continue at Farm 1, halting the pelting process. Based on Farm 1 findings, a letter was issued to all mink producers urging the implementation of enhanced biosafety measures as outlined by the draft federal guidelines.
2.2 Repeated farm inspections on all mink farms
Finding of limited safety measures at Farm 1	Purpose: To monitor implementation and feasibility of biosafety measures required by PH, MAFF or WorkSafeBC. Action: Inspections were repeated at all active mink farms on an ongoing basis.	Initial inspections on all mink farms found weaker biosafety measure implementation than those recommended by the mink farm biosafety advisory group. Implementation of recommended enhanced biosafety measures improved over time with the issuance of a FH PH Class Order mandating enhanced measures, along with subsequent inspections and feedback to mink farm operators.
3. Formal communications with mink farm operators, including Provincial Health Officer and Chief Veterinarian letter to operators on December 6, 2020, and follow-up meetings between PH, MAFF and industry in January and February 2021
Weak biosafety measures observed on Farm 1 during outbreak investigation, and in other farms’ inspections triggered by the Farm 1 outbreak	Purpose: To communicate PH concerns to mink farm operators and achieve improved biosafety measures on mink farms. Action: The letter reminded operators of the mandatory requirement for a written COVID-19 Safety Plan and for those plans to be posted. It strongly recommended all mink farms to immediately review and strengthen those Safety Plans to implement the measures recommended for mink farms that were outlined in a biosecurity advisory from the Canadian Food Inspection Agency and the Public Health Agency of Canada. Those measures included the use of fitted respirators (N95 or equivalent) especially for pelting (or, if unavailable, medical masks), gloves, and eye protection, as well as viral testing of workers before pelting and on a weekly basis until pelting conclusion. Follow-up meetings (one with a “town hall” format) were instituted for mink farm operators to share information about the industry operations, for public health and MAFF to share more about the science, and to support discussion about control measures.	Some operators’ COVID-19 Safety Plans were found lacking, and some reported that they thought recommendations were challenging, confusing, and unnecessary. To improve compliance, FH issued a Class Order to all mink farms mandating enhanced measures be implemented before pelts, animals, or products could be moved on or off farms. OHC subcommittees were also created to issue BC-specific biosafety recommendations balancing risk reduction with practicality considerations and challenges. Meetings led to greater understanding of mink farm operations and increased overall buy-in for public health measures, although perceptions still varied across the industry.
4. Mink euthanasia for the purpose of pelt production on Farm 1, December 16–24, 2020
Concern that maintaining a stock of thousands of mink infected with SARS-CoV-2 at Farm 1 would promote further viral replication and mutation, on the one hand, versus concern of viral transmission to workers	Purpose: To decrease further viral replication with associated risk of mutation among infected mink on Farm 1. Considerations: There were thousands of animals left to skin at Farm 1 when the process was halted. On the one hand, keeping the herd at its large size could enable further viral replication and promote the emergence of more mutations, and from the producer’s perspective, mink needed to be skinned as soon as possible before aging decreased pelt value, among other considerations. On the other hand, the skinning process is considered high risk because of compression of the mink’s lungs expelling respiratory secretions, potentially generating aerosols, and workers being in very close proximity to each other and to the mink. Culling of the entire herd, disposal, and disinfection was considered, to decrease ongoing risk of transmission from regular operation. However, this was ultimately decided against as it would have exposed a significant number of additional workers, was logistically complicated and had significant negative implications for the producers.	A decision was reached to allow euthanasia and skinning under strict biosafety measures, which could vary considering whether performed by previously infected workers or not. Farm 1 producer decided to proceed with euthanasia/skinning. Skins were not ultimately processed into pelts as processing facilities were unable to accept skins from an infected herd, causing financial strain.
5. Surveillance of farmed mink mortalities, starting in December 2020
Concerns of potentially undetected or delayed detection of mink outbreaks	Purpose: To quickly detect SARS-CoV-2 infection in mink herds. Considerations and action: The OHC had concerns that clinical surveillance with weekly written monitoring of illness and mortality, as suggested by the Canadian COVID-19 One Health working group ((21)) was unlikely to be adequate, and active surveillance had been recommended by both the World Health Organization and the World Organisation for Animal Health ((16)). Farm 1 had submitted mortalities upon request by MAFF following detection of the farmworker outbreak, while Farm 2 submitted mortalities for testing based on herd signs or excess mortality. Participation in mandatory mink mortality surveillance regardless of excess mortality or compatible signs was ordered December 14, 2020, with the start of collection in the following month. The goal of mandatory mortality surveillance was to monitor for SARS-CoV-2 infection among mink herds in a timely manner, regardless of signs or symptoms, enabling swift quarantine and detection of mutations and minimizing transmission to workers. Based on the Canadian Food Inspection Agency guidelines, it was estimated that weekly collection of 15 mink mortalities per farm would provide a 95% surveillance sensitivity to detect an outbreak; therefore, farms were required to provide up to 15 per week. Logistical considerations, both from farms and from testing processing capacity, suggested five mortalities per week would be more feasible, estimated to provide 65% sensitivity. FH environmental health officers collected frozen and sealed mink carcasses from both non-infected and infected premises each week and brought them to MAFF’s Animal Health Centre for SARS-CoV-2 testing. Any non-negative samples were sent to the National Centre for Foreign Animal Disease for confirmatory polymerase chain reaction testing and to the BCCDC Public Health Laboratory for whole-genome sequencing, if positive.	On December 23, 2020, mink mortalities collected the prior week from a second farm (Farm 2) returned SARS-CoV-2-positive, and an additional outbreak was declared; mink displayed slight clinical signs and increased mortality (fewer than 3%). Farm 2 owners euthanized their small herd (fewer than 1,000 mink) without request by PH or MAFF. Farms had challenges in providing even the five mortalities per week due to the low mortality rate for many months of the year and small herd sizes in BC. On May 14, 2021, Farm 3 mink mortalities collected in early May were confirmed SARS-CoV-2-positive. The outbreak investigation uncovered mink exposure to an infectious worker who tested positive approximately 6 weeks earlier (within 14 days of the first dose of the vaccine), harbouring the same strain as positive mink. Ongoing mortality collection enabled detection of Farm 3 mink cases months after the outbreak start, enabling timely assessment of viral propagation and evolution in the herd; however, mink mortality freezing, collection, thawing and testing was resource-intensive.
6. Farm quarantine by BC Chief Veterinarian
Suspicion or confirmation of a SARS-CoV-2 infection in a mink herd (Farm 1, Farm 2 and Farm 3)	Purpose: To limit potential spread of the virus from infected mink farms. Action: The Chief Veterinarian placed a quarantine order on infected premises that restricted all movements of animals, products and goods off of the farm. New enhanced protocols of disinfection of vehicles, products, and goods were put in place before authorization was given for non-essential activities.	On Farm 1, the herd was deemed free of disease as of February 24, 2021, after 2 sets of 65 samples taken 2 weeks apart were found to be all negative. As the Farm 2 herd was culled, it did not need to be declared free of disease. The Farm 3 herd was still considered infected by the end of this study period. Farm sites remained in quarantine until the determination that the farm environment was decontaminated.
7. Mandatory worker COVID-19 testing, December 2020–January 2021
Concerns of undetected asymptomatic worker infection or avoidance of testing by symptomatic workers	Purpose: To detect past or current COVID-19 infection in mink farmworkers. Action: In Mid-December 2020, mink farmworkers (n=102) were mandated to complete COVID-19 virology and serology tests before being allowed back on farms. Farm 2 workers had repeated viral and serological testing in January 2021 after pelting completion, to detect missed infections.	No viral or serological tests taken in December 2020 and January 2021 returned SARS-CoV-2-positive.
8. Voluntary worker COVID-19 surveillance, starting in January 2021
Concerns of undetected asymptomatic worker infection or avoidance of testing by symptomatic workers	Purpose: To improve detection of COVID-19 infection in mink farmworkers. Action: Public Health implemented a free-of-charge, weekly surveillance program for mink farmworkers in January 2021, utilizing self-collected saline gargle samples ((22,23)). BCCDC PH nurses trained workers on gargle sample self-collection and associated processes, minimizing ongoing PH staffing requirements and increasing testing acceptability, while maintaining sensitivity compared to nasopharyngeal swabs ((22,23)) and still enabling whole genome sequencing by the BCCDC Public Health Laboratory. A same-day medical courier collected samples from farms for delivery to the BCCDC Public Health Laboratory, with 0–2 days from sample collection to results. Indeterminate results led to repeated tests.	All active farms (6 farm units including Farm 1) participated by the end of February 2021. Between February 21 and May 31, 2021, an audit showed active workers’ weekly participation at 86%–100% per farm. The worker surveillance program detected 11 COVID-19 cases. One additional positive worker was detected through community testing following household exposure. Detection of positive workers triggered increased testing (2–3 times per week). Further, if an infectious worker had been near mink, 3 weeks of live mink sampling also occurred. Some farms voluntarily maintained twice or thrice-weekly testing.
9. Wildlife surveillance, starting in January 2021
Concern regarding SARS-CoV-2 transmission to surrounding wildlife	Purpose: To detect potential SARS-CoV-2 transmission to wildlife from escaped mink or feral cats ((17,18,24)). Action: Wildlife surveillance around Farm 1 and Farm 2, utilizing wildlife trapping, testing, and video footage, occurred from January to March 2021. Wildlife surveillance was also undertaken around Farm 3 in summer 2021.	Virology and serology tests were negative on all 65 animals sampled around Farm 1 and Farm 2. Repeated wildlife surveillance surrounding Farm 3 in summer 2021 located no infected wildlife but did detect 3 escaped mink that tested positive ((25)).
10. Mandatory worker COVID-19 vaccination, April 2021
Availability of COVID-19 vaccine supply and prioritization of vaccines for high-risk workplaces, including mink farms	Purpose: To reduce risk of SARS-CoV-2 transmission to mink herds from mink farmworkers. Action: On April 15, 2021, a new FH PH Order permitted only vaccinated workers to work in proximity to mink.	Most workers opted to be vaccinated (~90% first dose at the time of the Order including unmandated workers). Pfizer-BioNTech (BNT162b2) vaccination was offered to workers beginning March 17 and subsequently to their household members with excellent uptake; second doses were offered in May–June, with more than 90% worker uptake. Out of the 12 COVID-19-positive workers, 33% were unvaccinated, 25% partially vaccinated (onset or positive test more than 14 days post-first dose), and 42% fully vaccinated (more than 14 days post-second dose) at the time of infection.
11. Joint rapid qualitative risk assessment, June 2021
Need for an up-to-date, BC-specific assessment on the risk of mink farm-related SARS-CoV-2 variant of interest emergence and community transmission to inform further response	Purpose: A formal risk assessment was undertaken to support decision-making regarding concerns related to SARS-CoV-2 and the mink farm industry in BC. Action: In June 2021, a multi-jurisdictional risk assessment was conducted as per best practices ((26)). National and provincial experts assessed potential scenarios’ probabilities, impacts, and uncertainties, using a modified Delphi approach (personal communication, V. Clair, 2021).	The likelihood of a variant of interest emerging in mink and circulating in the community over the next 5 years was evaluated as unlikely (moderate-high uncertainty) with minor to moderate impacts (moderate-high uncertainty). As a result, BCCDC recommended a moratorium on mink farming expansion. Following detection of SARS-CoV-2-positive escaped mink on Farm 3, the Provincial Health Officer issued a moratorium on expansion of the mink industry in late July 2021 ((27)).

Abbreviations: BC, British Columbia; BCCDC, British Columbia Centres for Disease Control; COVID-19, coronavirus disease 2019; FH, Fraser Health Authority; MAFF, Ministry of Fisheries and Oceans; OHC, One Health Committee; PH, Public Health; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2