Rapid antigen tests to the rescue: The new world without COVID restrictions

With COVID-19 restrictions easing across the country, including the lifting of capacity limits, ending proof-of-vaccination requirements, and elimination of indoor masking mandates, most Canadians remain uncertain what living with COVID-19 in a less restrictive way looks like. We need to understand that COVID is not over yet and that we still need to remain vigilant as restrictions lift. The idea that we must “live with COVID” is not new—we’ve been living with it over the past two years—but we do need to adjust to going back to some sense of normalcy recognizing that the threat is still out there, but we already know what works to prevent serious health outcomes and reduce transmission: getting fully vaccinated, including a third shot (booster), is the best way to avoid serious health outcomes from omicron; continuing to wear a medical-grade mask in high-risk settings such as poorly ventilated, crowded, indoor spaces where people can't physically distance; keeping at least a two-metre distance from others, especially if parties are unmasked; and staying at home and isolating for several days if symptoms develop. Rapid antigen tests (RATs) are a quick, easy and cost-efficient resource to have in our tool kit to quickly identify and isolate those with COVID-19 but can also be used to clear individuals out of isolation if symptoms are not due to COVID-19. They have also been effectively used in asymptomatic workplace surveillance programs where asymptomatic workers are tested 3-5 times a week to clear people to work and keep workplaces and workers safe. Using and interpreting them properly is key to meaningfully reduce disease spread. In recent weeks, there has been a compelling need to reassess testing strategies which employ the use of RATs given public health restrictions for PCR testing. While the specificity of a positive RAT is almost 100%, a recent Swiss study found RATs to have a lower sensitivity to the highly transmissible Omicron variant (BA.1), including its newly identified subvariant, BA.2, compared to previously circulating strains of SARS-CoV-2, including the more severe Delta variant2. Omicron remains the predominant strain circulating across the Canada and internationally due to its ability to cause re-infection and breakthrough infections in those who are fully vaccinated. Additionally, preliminary findings from research on the BA.2 subvariant has found it to be upwards of 33% more infectious than the original Omicron variant. Studies have also found that individuals infected with Omicron are infectious days before they test positive on a RAT. Due to these findings, a single negative RAT is insufficient to rule out a COVID-19 infection. Conversely, a single positive RAT is sufficient to conclude COVID-19 infection and isolate without the need for PCR confirmation testing. Given the negative impact isolation has had on individuals and communities, using RATs to test out of isolation in some situations can be very helpful. Serial testing, whereby multiple tests done 24 - 48 hours apart, can be used to clear symptomatic individuals from isolation. If an individual develops symptoms and is uncertain if they have COVID, they can use serial testing with RATs to determine their isolation requirements. If symptomatic, test with two RATs 24-48 hours apart: If any RAT is positive, isolate for 5-10 days depending on your age and vaccination status. If the first test is negative, continue to isolate and test again in 24 hours. If the second test is also negative, you are unlikely to have COVID-19 but should still isolate until symptoms have improved for 24 hours. You can then resume your normal activity but should still wear a mask when out of your house and avoid visiting high-risk setting such as hospitals and long-term care settings. In addition to serial testing strategies, a change in swabbing method is also recommended to increase the sensitivity of RATs to Omicron. A study out of South Africa, where the Omicron variant was first identified last November, found there are higher viral loads in saliva compared to nasal samples4. This study was corroborated with findings that Omicron is found in high viral loads in the bronchus and is associated with greater reports of upper respiratory symptoms such as sore throat and cough1. These are important findings as the standard for confirming COVID-19 infection has primarily been through nasal-collected samples. Swabbing, or sampling from, the anterior nares (nostrils) has been a popular means of sample collection as it is less invasive than others, such as from the nasopharyngeal or oropharyngeal areas, and can be self-administered. However, to optimize the sensitivity of RATs, and thus increase reliability of their results, experts recommend adoption of a combined oral-nasal swabbing method. The combined oral-nasal sampling method involves swabbing the inside of both cheeks plus the very back of the throat or tongue followed by both nostrils using the same swab – best to get the order of swabbing correct here. Using this combined method increases the sensitivity of RATs to be comparable to the sensitivity of nasopharyngeal samples which are considered the gold standard for testing but require a trained, regulated health care professional to perform. Along with COVID-19 vaccination, RATs have played a key role in the easing of restrictions and re-opening of businesses, schools, and venues across the country. RATs continue to be a valuable resource to quickly identify and isolate those with COVID-19, furthering our collective progress towards the end of the pandemic. Considering the recent findings, it is strongly recommended that individuals and organizations adopt the updated RAT strategies, including the combined oral-nasal sampling method and serial testing for both asymptomatic and symptomatic individuals, as we all adjust to a new way to live with COVID without ongoing restrictions. Dr. Jonathan Davids is the corporate chief medical director of DriverCheck and Melanie Smith, R.N., is senior COVID testing implementation manager at DriverCheck. Founded in 1996, DriverCheck (DriverCheck.ca) provides workplace medical testing and assessments. References Adamson, B., Sikka, R., Wyllie, A. L., & Premsrirut, Prem. (2022, January 5). Discordan SARS-CoV-2 PCR and rapid antigen test results when infectious: A December 2021 occupational case series. doi: https://doi.org/10.1101/2022.01.04.22268770 Bekliz, M., Perez-Rodriguez, F., Puhach, O., Adea, K., Marques Melancia, S., Baggio, S., Corvaglia, A., Jacquerioz-Bausch, F., Alvarez, C., Essaidi-Laziosi, M., Escadafal, C., Kaiser, L., & Eckerle, I. (2022, January 17). Sensitivity of SARA-CoV-2 antigen-detecting rapid tests for Omicron variant. doi: https://doi.org/10.1101/2021.12.18.21268018 Jüni, P., Baert, S., Corbeil, A., Johnstone, J., Patel, S. N., Bobos, P., … McGeer, A. (2022, February 10). Use of rapid antigen tests during the Omicron wave. https://covid19-sciencetable.ca/sciencebrief/use-of-rapid-antigen-tests-during-the-omicron-wave/ Marais, G., Hsiao, N., Iranzadeh, A, Doolabh, D., Enoch, A., Chu, C., Williamson, C., Brink, A., & Hardie, D. (2021, December 24). Saliva swabs are the preferred sample for Omicron detection. doi: https://doi.org/10.1101/2021.12.22.21268246 World Health Organization. (2022, February 22). Statement on Omicron sublineage BA.2. Retrieved from https://www.who.int/news/item/22-02-2022-statement-on-omicron-sublineage-ba.2

Rapid antigen tests to the rescue: The new world without COVID restrictions

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