Chamber and committees

Asymptomatic and pre-symptomatic transmission of COVID-19 occurs, which is a challenge for suppressing the virus as there is a risk of individuals mixing with others, whilst not presenting symptoms. The Scottish Government does not hold information on the transmission rates of COVID-19 by only asymptomatic and pre-symptomatic people. For this reason, the decision-making process around asymptomatic and pre-symptomatic transmission, as well as any other COVID-19 related issue, will continue to be based on the available scientific and medical evidence from:

• the World Health Organisation;

• the UK Scientific Advisory Group for Emergencies;

• the Scottish Government COVID-19 Advisory Group.

Please note that SAGE and the Scottish Government COVID-19 Advisory Group, as well as other UK advisory groups such as the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) and the Scientific Pandemic Influenza Group on Modelling (SPI-M), discuss the emerging evidence of transmission of COVID-19 separately. Each of them also publishes separate papers, which may cover the asymptomatic and pre-symptomatic transmission of the virus.

The paper ‘SARS-COV-2: Transmission Routes and Environments, 22 October 2020’ (available from SAGE meetings, October 2020 - GOV.UK (www.gov.uk)) reported that:

“The contribution of asymptomatic infection to transmission will depend on:
‎ • the relative degree of infectiousness (this is approximately 1/3 as infectious compared to those who have or go onto have symptoms [45]),
‎ • the proportion of infections that are asymptomatic (recent estimates suggests 20% (95% CI 17%–25%) of individuals remain asymptomatic throughout the infection [45])
‎ • the relative number of contacts (asymptomatic cases are unlikely to self-isolate so may have more contacts than symptomatic cases). It is plausible therefore that both asymptomatic and pre-symptomatic cases make a significant contribution to transmission. People with mild symptoms (paucisymptomatic), who feel otherwise well, still carry large amounts of virus in the upper respiratory tract, which might particularly contribute to transmission of SARS-CoV-2 [43].”

The Coronavirus (COVID-19): Scotland’s Strategic Framework was published on 23 October 2020, setting out how we will work to suppress the virus to the lowest possible level and keep it there, while we strive to return to a more normal life for as many people as possible and tackle the four harms we know the virus causes. We will keep our approach under review, informed by scientific evidence and continued engagement with business and communities.

Sources:
‎ 43. Cevik M, Tate M, Lloyd O, Maraolo AE, Schafers J, Ho A. SARS-CoV-2, SARS-CoV-1 and MERS-CoV viral load dynamics, duration of viral shedding and infectiousness: a living systematic review and meta-analysis. medRxiv 2020: 2020.07.25.20162107.
‎ 45. Buitrago-Garcia D, Egli-Gany D, Counotte MJ, et al. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. PLOS Medicine 2020; 17(9): e1003346.