Asymptomatic shares of infections

What proportion of SARS-CoV-2 infections show no symptoms?

The claim ‘one in three infected people show no symptoms’ appears in government statements:

Around 1 in 3 people have coronavirus (COVID-19) without displaying any symptoms.

(Image: HM Government/Facebook)

We need to think, with care, about what such a claim could mean.

• Asymptomatic and pre-symptomatic: Is the intention to only capture symptoms at the point of testing? Should we distinguish between showing no symptoms at all and developing symptoms later?
• A list of symptoms: What is the list of symptoms? Do we say a person has ‘no symptoms’ if they present with something atypical? How do we disentangle listed symptoms for other reasons? Could SARS-CoV-2 variants show distinct profiles of symptoms?
• The population: What is the population under consideration? Would we expect differences in this asymptomatic share between different groups?

(Image: A Rapid Review of the Asymptomatic Proportion of PCR-Confirmed SARS-CoV-2 Infections in Community Settings)

The figure itself comes from a rapid review on the literature of symptoms in confirmed cases. The search, only including studies written in English, yielded 22 studies.