People with ‘silent’ or asymptomatic Covid-19 infection have as much coronavirus in their noses and throats as those with symptoms, warn researchers.

The study, published in the journal Thorax, revealed that these ‘silent’ people may have a key role in driving the spread of Covid-19.

For the findings, the researchers from Asan Medical Centre in South Korea, compared the viral load of 213 people, all of whom had tested positive for SARS-CoV-2, but not all of whom had symptoms of Covid-19 infection.

People infected with the SARS-CoV-2 virus, but who don’t have symptoms, still carry potentially transmissible virus, known as the viral load.

Following a large cluster outbreak of Covid-19 in Daegu City, South Korea, early on in the pandemic, the close contacts of this cluster (a religious group) were traced.

This uncovered more than 3,000 cases of Covid-19, ranging in symptom severity from none to severe.

Those with mild or no symptoms were admitted to dedicated care facilities for isolation and monitoring.

The 213 participants in this study had been admitted to one such facility.

They were classified as symptomless if they had none of the following: fever, chill, muscle pain, fatigue, runny nose, blocked nose, loss of taste or smell, sore throat, cough, headache, dizziness, loss of appetite, etc.

Before the isolation period — an average of six days from the first swab test — around a fifth (19 per cent) people didn’t develop any symptoms.

Of the remaining 172 (81 per cent) with mild symptoms, 144 were retested, adding up to a total of 183 who were included in the final analysis.

Over half of those without symptoms (54 per cent) tested positive for SARS-CoV-2, as did nearly two thirds of those with mild symptoms (64 per cent).

There was no significant difference in the viral load between the two groups.

“Our data adds further support to the general public use of face masks, regardless of the presence of symptoms,” said study lead author Sung-Han Kim.

The researchers noted that most of the participants were also in their 20s and 30s so the findings might not apply to other age groups.

Further studies are needed to clarify whether the persistence of viral DNA in people without any symptoms warrants precautionary quarantine measures, they stressed.