9 April 2020, updated on 20 April 2020 – Rapid systematic review

The role of asymptomatic SARS-CoV-2 infections: rapid living systematic review and meta-analysis

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  1. What is the proportion of people that becomes infected with SARS-CoV-2 infection who do not experience symptoms at all during their infection?
  2. Amongst people who become infected with SARS-CoV-2, what proportion has no symptoms at the time of testing, but develops symptoms later?
  3. What proportion of SARS-CoV-2 infections is accounted for by people who are either asymptomatic throughout infection, or pre-symptomatic?


  1. We estimate, from empirical data, that up to 40% of people who become infected with SARS-CoV-2 will have an asymptomatic infection and will not develop symptoms during the course of their infection.
  2. Based on empirical studies, the proportion of people detected to have asymptomatic SARS-CoV-2 that goes on to develop symptoms is uncertain.
  3. Mathematical modelling studies predict that 50-60% of all SARS-CoV-2 tranmsission is the result of transmission from either asymptomatic or pre-symptomatic individuals.

Date of request: 30/3/2020
Date of response: 9/4/2020 amd 20/4/2020

In response to request from: NCS-TF Advisory Board

Comment on planned updates: This is a living systematic review. The search was updated on 20.04.2020.

Expert groups and individuals involved: Public Health

Contact persons: Prof. Nicola Low, Institute of Social and Preventive Medicine, University of Bern, Switzerland, e-mail nicola.low@ispm.unibe.ch

As the Swiss National COVID-19 Science Task Force has been disbanded as of 31 March 2022, no further epidemiological assessments, scientific updates or policy briefs will be published in the future. All previous publications, pages and information of the Science Task Force remain available on this website.