Asymptomatic infection has similar SARS-CoV-2 viral load to mild COVID-19

Simon Collins, HIV i-Base

A lack of correlation between levels of SARS-CoV-2 and symptoms in people with mild COVID-19 was reported in a recent study showing that people with asymptomatic infection do not present lower risks for transmission. 

These data are important given the UK recommendation to continue prevention measures as lock down is eased.

The study included PCR results from 39 asymptomatic and 144 symptomatic participants attending a community clinic in South Korea. Overall, median age was approximately 25 years (IQR 21 to 46), 50% were male/female and one-fifth of people diagnosed SARS-CoV-2 positive but without severe symptoms were asymptomatic.

PCR levels in the upper respiratory tract were similar in these two groups, with no significant differences (p>0.99).

However, the study also reported that more than half of these young, mildly symptomatic patients, showed persistent positive upper respiratory RT-PCR results at the follow-up visit two weeks later.


A lack of symptoms has never been considered uninfectious as the main difference between SARS-2 and SARS-2 is that transmission occurs in the pre-symptomatic stage.

Even though SARS-CoV-2 viral load doesn’t always correlate with infectiousness, these results might be useful for recognising potential transmission risk in people who remain asymptomatic throughout infection, and who are therefore less likely to be diagnosed.

However, being PCR positive at two weeks is very common with inpatients – but this does not help knowing if this is a replicant competent virus that can infect others or it just a bit of dead virus.


Ra SH et al. Upper respiratory viral load in asymptomatic individuals and mildly symptomatic patients with SARS-CoV-2 infection. Thorax 202176:61-63. (1 May 2021). (html) (PDF)

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