Meeting 37 of the CSA COVID-19 Expert Panel

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As part of the response to the COVID-19 pandemic, the Chief Science Advisor of Canada created the Expert Panel on COVID-19 to advise her on the latest and most relevant scientific developments. This information assists the CSA in providing current, cross-disciplinary and independent advice to the Prime Minister and government.

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Overview of discussions

Held by teleconference on December 18, 2020

The following discussion reflects evidence and scientific knowledge up to December 17th.

Participating experts

• Mona Nemer PhD, Chief Science Advisor of Canada (chair)

Disease modelling

• Daniel Coombs PhD, University of British Columbia

Risk and behavioural sciences

• Kim Lavoie PhD, Université du Québec à Montréal
• Louise Lemyre PhD, University of Ottawa

Biomedical and clinical sciences

• Joanne Langley MD, Dalhousie University
• Allison McGeer MD, Mount Sinai Hospital, University of Toronto
• Samira Mubareka MD, Sunnybrook Research Institute
• Guillaume Poliquin MD, PhD, Public Health Agency of Canada
• Supriya Sharma MD, Health Canada
• Cara Tannenbaum MD, Université de Montréal, Health Canada Departmental Science Advisor

Invited expert

• Pascal Michel DVM PhD, Departmental Science Advisor, Public Health Agency of Canada

Other

• Luc Gauthier, Office of the Chief Science Advisor (support)
• George Enei P. Eng, Office of the Chief Science Advisor (support)
• Vanessa Sung PhD, Office of the Chief Science Advisor (support)
• Priya Gurnani PhD, Office of the Chief Science Advisor (support)

Considerations for reducing the required quarantine period for travellers

• There is emerging evidence suggesting that a shortened quarantine period (i.e. fewer than 14 days) for travellers could be considered, potentially in combination with testing and other conditions.
• The experts discussed the key considerations, evidence, and challenges associated with changing the traveller quarantine guidelines.

Modeling

• Recent modeling studies estimate that the difference in benefit between a quarantine period of 10 or 14 days is small in most circumstances, and that a shorter quarantine period combined with testing could be a possible alternative to a full 14-day quarantine^{Footnote 1}, ^{Footnote 2}.
• Closer scrutiny of published modelling studies could support this determination.

COVID-19 infectivity period

• Given the available evidence up until December 17th, the period of transmissibility for previously healthy individuals is typically 7-10 days after symptom onset. Beyond this period, the probability of transmission diminishes substantially, though outlier cases do occur.
  • Individuals who are immunocompromised, or have a severe disease, can shed virus for a much longer period of time. These individuals do not represent a major driver of transmission events.
• Transmissibility in children is still under active debate, though the general consensus is that children under the ages of 8- 10 years of age are less efficient transmitters. Teenagers appear to transmit at a similar rate to adults. The lack of symptoms in children could increase opportunities for transmission, as their guardians would not be aware of the active infections.
• Another complexity of using a test to exit quarantine is that some individuals may test positive late into their quarantine or with high Ct (threshold cycle) values. It is unclear how one would determine whether it is an old or new infection (e.g. due to quarantine breach), whether they are infectious, and how these cases would be handled.

Regional context

• The risks associated with reducing the quarantine period is greater in areas with low community prevalence. The downstream effect of a single imported case in a place with fewer COVID-19 cases would have a greater impact than in a place that already has high levels of community transmission.
• Models and policies need to consider demographics, such as Northern and remote communities, where transmission occurrences are low, and they do not readily have access to rapid testing.
• Different communities have different abilities to manage the risks and demands associated with a shortened quarantine period plus testing. Ideally, quarantine guidelines would be specific to local contexts, recognizing it would be very challenging to have contextualized national guidelines.

Pilot studies and initiatives in Canada

• The Alberta COVID-19 Border Testing Pilot Program^{Footnote 3} allows for a shortened quarantine period for international travellers, combined with two negative test results and a number of restrictions, including a ban on visiting hospitals, nursing homes, or other higher risk places.
• Nova Scotia implemented a 14-day quarantine period plus testing strategy for all students entering from outside the “Atlantic Bubble”. Follow-up surveys found that the 14-day quarantine period adversely affected the students’ mental health.
• Both the Alberta and Nova Scotia initiatives, as well as another pilot project conducted at Toronto Pearson Airport, found relatively few positive COVID-19 cases. The pre-test probability of an average traveller appears to be low.
• To better monitor for COVID-19 importation events as border measures change, the National Microbiology Laboratory (NML) is working with CanCOGeN to develop lineage heterogeneity indices on a weekly basis. If there is an appearance of a lot of heterogeneity, that would indicate likely importation events.
  • Of note, this approach will require a reasonable turnaround time for sequencing and a robust sampling framework to identify target travellers.

Behavioural considerations

• The iCARE studies have consistently found that 13% of respondents report that they do not adhere to quarantine when they return from travel. It is possible that a reduction in the duration of quarantine may increase compliance^{Footnote 4}.
• Reducing quarantine periods could encourage more people to travel, as the current 14-day quarantine is a significant deterrent. If the level of travel increases, the previously established predictive models may no longer be applicable.

Limitations in lab capacity

• A test-dependant reduction in quarantine periods would result in an increase in testing demand for already resource-strained labs.
• In addition to challenges with lab capacity, the timely delivery of samples into labs should be considered.
• There are opportunities to enlist academics and researchers to help with processing tests, but not all clinical diagnostic labs are comfortable with this approach.
• Point-of-care rapid tests could be helpful, but they would need to be validated and piloted before broad implementation.
  • Rapid tests are able to produce results in real time, and their level of sensitivity may better discern a person’s infectiousness compared to PCR tests.