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Optimal Omicron isolation times and the growing science behind them

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Recently reduced COVID isolation times do not reflect new research which finds a large percentage of individuals remain potentially infectious beyond five days.

As the highly transmissible Omicron variant continues to spread and with less access to COVID testing and contact tracing, other public health measures, including isolation, become more critical.

Mandatory isolation of those with COVID is intended to reduce contact with others for the duration of their infectious period. This said, isolation recommendations are now varying. This has prompted many key questions. For instance, are shortened isolation periods sufficiently protective or will they prolong the pandemic?

Recent studies support longer isolation periods

A recent study by researchers at Harvard University offers some answers. They collected and analyzed 10,324 PCR SARS-CoV-2 viral samples collected from 537 participants (players, team and arena staff and other affiliates) with the National Basketball Association (NBA) occupational health program. The samples were administered by a trained provider and collected between July 5th, 2021 and January 10th, 2022. The program involved frequent testing as well as testing triggered by COVID-19 symptoms and possible contact with infected individuals.
 
Viral load was measured using the cycle threshold, a proxy for infectivity and is correlated with cycle threshold values less than 30 (Ct ≤30). For all infections, researchers determined the percentages with Ct ≤30. Tests results for Omicron and Delta were also separated.

From their analysis the researchers report:
  • Day 11 after detection, all individuals reached a cycle threshold of greater than 30 and all tested PCR negative on day 15.
  • Of 27 Omicron-infected individuals testing positive less than one day after a previous negative or inconclusive test, 52 per cent were PCR positive (Ct ≤30) at day five, 25 per cent at day six, and 13 per cent on day seven post detection
  • Of 70 Omicron-infected individuals detected greater than two days after a previous negative or inconclusive test, 39.1 per cent were PCR positive (Ct ≤30) at day five, 33.3 per cent at day six, and 22.2 per cent on day seven post detection.
  • Omicron infections had a mean duration of 9.87 days relative to 10.9 days for Delta infections.

The authors concede NBA test subjects may not be representative of the population and infectiousness can be influenced by a number of factors, nonetheless they still conclude, “The uncertainty about the true timing of the end of the infectious period for individuals identified as infected with COVID-19 outside of frequent testing regimens argues that a cautious approach for shortening isolation may be warranted.

Another recent study, not yet peer reviewed, but published online by Japan’s National Institute of Infectious Diseases, comes to a similar conclusion. In a cohort of hospitalized Omicron cases in Japan, viral load was highest three to six days after symptoms began. A large proportion of cases had high viral loads up to nine days post detection. Viral shedding was limited from day 10.

The Japanese study, recently cited by Dr. Teresa Tam, Canada’s Chief Public Health Officer of Health, is among the evidence which finds the communicable period for the Omicron variant is no shorter than for previous variants. Based upon the science, the Public Health Agency of Canada’s Recommendations for isolation of COVID-19 cases in the community maintains an isolation period of 10 days.

Shortened isolation periods. Science vs societal impacts.

While many are monitoring the emerging science on when and for how long a person is most infectious, COVID-related illness and isolation is creating significant staffing shortages for businesses. Is this the time to exercise greater precaution or should we ease up restrictions? Will sending potentially infectious persons back into the public or workplaces cause a greater problem?
 
Decision makers appear to consider these impacts and questions when they revised public health guidance on isolation times. The U.S. Centers for Disease Control and Prevention (CDC) noted as much in their rationale for shortening isolation and quarantine times for the general population. The CDC’s revised recommendations require an isolation period of at least five days, regardless of vaccination status, for individuals who test positive or have mild symptoms. When it comes to health care workers though isolation provisions come with a very detailed response depending on severity of illness and/or immune status.

Ontario has similarly revised its COVID isolation guidance. However, Ontario rules distinguish between the fully vaccinated and those unvaccinated, upholding the 10-day isolation period, for the latter. Health care workers and the like also have a different set of rules. “To ensure sufficient staffing levels,” Ontario stipulates infected unvaccinated or immunocompromised persons who work in a “high-risk setting, including hospitals, long-term care, retirement homes, [or] congregate living settings … will have the opportunity to return to work early on day seven of their isolation, with a negative PCR test, or two negative rapid antigen tests on day six and seven.”

Employers' legal OHS obligations

Under Ontario’s Occupational Health and Safety Act (OHSA) employers are charged the greatest legal responsibilities for ensuring safe work, including the duty to take every precaution reasonable for the protection of workers. During the COVID crisis this demands a layered approach to controlling virus transmission and should include access to rapid tests, mandatory vaccination requirements, improved proper masking, enhanced ventilation and physical distancing.

Well-trained workplace health and safety representatives offer a layer of protection too. If your workplace employs 20 or more workers or a designated substance is onsite, the OHSA requires the establishment of a JHSC. In this case, employers must also "carry out" approved Certification training for at least two members of the JHSC, one worker representative and one management representative, including Certification Part ICertification Part II and Certification Refresher

Meantime, WHSC-scheduled in-person training includes Working at Heights and Working at Heights Refresher training.



Don’t see what you need? Beyond the scheduled classes listed above, and where participant numbers warrant, we can work with you to coordinate almost any of our training courses, including our COVID awareness training, for all workers, workplace representatives and supervisors.

Contact a WHSC training services representative in your area.
Email: contactus@whsc.on.ca
Visit: www.whsc.on.ca
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