corona virus-Covid19

More Than Half of COVID-19 Infections Acquired from Asymptomatic Carriers Interview with:

Jay C. Butler, MD, FAAP, MACP, FIDSA Deputy Director for Infectious Diseases Centers for Disease Control and Prevention Atlanta, GA  30333

Dr. Butler

Jay C. Butler, MD, FAAP, MACP, FIDSA
Deputy Director for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA  30333 What is the background for this study?

Response: There are still disagreements about the significance of transmission of SARS-CoV-2 from asymptomatic persons.  It has been known since at least March 2020 that, unlike the closely related coronavirus that causes SARS, transmission of COVID-19 from asymptomatic and presymptomatic persons occurs and that at least 30% of infected persons do not develop symptoms.  Estimating the proportion of transmissions from persons without symptoms informs the decision analysis for prioritization of community mitigations opportunities:  wearing of masks, social distancing, and hand hygiene. If only a low proportion of transmission occurs from people without symptoms, these interventions would be less likely to control transmission when broadly applied in the community.  On the other hand, if a significant proportion of spread is from infected persons without symptoms, the value of these measures is enhanced.

Additionally, obtaining strategic and systematic screening tests for SARS-CoV-2 to identify and isolate persons without symptoms in selected settings, such as congregational housing settings, will have greater potential impact if spread from persons without symptoms is common. What are the main findings?

Response: First, it should be clear that while isolation of persons with symptoms or who are known to be infected is of benefit, it will have a limited impact in limiting ongoing transmission.

Second, under a wide range of base values, more than half of infections are acquired from persons without symptoms.  This highlights the opportunity to slow spread by wearing masks, particularly when around others outside of the home, avoiding crowds and keeping distance from others, particularly when indoors, and performing hand hygiene.  It also highlights the potential to slow spread through strategic use of screening tests and simple environmental controls, such improving ventilation by opening a window when possible. What should readers take away from your report?

Response: Additional data that would be helpful include further assessment of the efficacy of various types of masks used in the in community, the impact of new variants on the transmission dynamics and base values used in this decisional analysis, and the optimal strategies for use of laboratory resources to screen persons without symptoms. What recommendations do you have for future research as a result of this work?

Response: Controlling the COVID-19 pandemic requires controlling the “silent pandemic” of transmission from persons without symptoms. The community mitigation tools need to be utilized broadly to slow spread of SARS-CoV-2 from all infected persons at least until safe and effective COVID-19 vaccines are widely available and used.  This is particularly important as at least one variant (B.1.1.7) with strong evidence of increased potential for transmission have emerged and have potential for global spread.



Johansson MA, Quandelacy TM, Kada S, et al. SARS-CoV-2 Transmission From People Without COVID-19 Symptoms. JAMA Netw Open. 2021;4(1):e2035057. doi:10.1001/jamanetworkopen.2020.35057



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Last Updated on January 8, 2021 by Marie Benz MD FAAD