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Important Update: CoV Transmissibility

Updated: Dec 28, 2021

Just a brief update: Yesterday, one of the most significant papers relating to this virus was published. In the paper they used contact tracing data to estimate the window in which people are infectious and importantly are able to infect others.

Research with the original SARS and the Flu virus show that the sub-clinical infectious window is only 24 hours. This is the window where you feel and look fine, but are actively shedding the virus into the environment. When you are feeling sick people you stay home (usually), when you look sick people avoid you. So sickness avoidance behavior limits the spread of the virus during the clinical infectious phase.

In contrast, the sub-clinical infectious period for SARS-CoV2 is estimated to be as large as 5 days. Meaning, you look and feel fine for those 5 days, but you are actively shedding the virus into the environment. The authors estimate that 44% of all infections happen in this sub-clinical/pre-symptomatic infectious window.

This finding has profound implications for our ability to socially engineer the control of this virus. For example,

  • Temperature readings are not a good indicator of being infectious.

  • I will have to revise my opinion on jogging and riding in together: if the sub-clinical infectious period is as large as they predict, and you are truly with no symptoms, then more caution is needed while exercising.

  • It also highlights the critical importance of contact tracing and quarantine. If you have been in contact with someone who is, post-meeting, diagnosed with COVID-19, you need to quarantine yourself for 14 days.

Please note, this does not change anything for you if you are practicing appropriate social distancing. And the work emphasized, that in-home (close contact transmission) was the most important factor. But it highlights, that even if you feel fine and look fine, you may be actively shedding the virus in to the environment and inadvertently infecting others.

It also does strongly suggest that mask wearing, to limit your respiratory emissions into the environment, will be an important tool to limit the spread of the virus (now and post-lockdown).

About the author

Erin S. Bromage, Ph.D., is an Associate Professor of Biology at the University of Massachusetts Dartmouth. Dr. Bromage graduated from the School of Veterinary and Biomedical Sciences James Cook University, Australia where his research focused on the epidemiology of, and immunity to, infectious disease in animals. His Post-Doctoral training was at the College of William and Mary, Virginia Institute of Marine Science in the Comparative Immunology Laboratory of late Dr. Stephen Kaattari.

Dr. Bromage’s research focuses on the evolution of the immune system, the immunological mechanisms responsible for protection from infectious disease, and the design and use of vaccines to control infectious disease in animals. He also focuses on designing diagnostic tools to detect biological and chemical threats in the environment in real-time.

Dr. Bromage joined the Faculty of the University of Massachusetts Dartmouth in 2007 where he teaches courses in Immunology and Infectious disease, including a course this semester on the Ecology of Infectious Disease which focused on the emerging SARS-CoV2 outbreak in China.

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