Primary-age children infected with the coronavirus have much lower viral loads than adults with Covid-19, a study found.
Viral load – the amount of virus a person harbors – has been associated by some scientists with increased transmissibility, although these claims are debated.
Data from public health officials in the Netherlands show a 16-fold difference in the amount of virus between the over-80s and children under the age of 12.
Rapid antigen tests, such as the touted 15-minute screening used in schools and airports, are also likely to be less accurate for children than adults due to their smaller load, the researchers say.
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This graph shows the Cp value for coronavirus patients sorted by age. Cp is a measure of how many cycles of PCR analysis, which amplified a genetic signal, are required to detect a SARS-CoV-2 signal. The higher the number, the lower the viral load. “The median Cp values between the oldest (> 79 years) and the youngest (<12 years) population differed more than 4 PCR cycles, suggesting an approximately 16-fold difference in viral load," the researchers write.
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More than a quarter of a million people in North Holland were tested between January 1, 2020 and December 1, 2020.
Of these, 211,933 were done by qualified healthcare providers, with a viral load data of 18,290.
All these swabs were processed by the same regional laboratory in the Netherlands to ensure that the tests were processed and analyzed in the same way.
“ To our knowledge, this is the first study to evaluate SARS-CoV-2 viral load distributions in a large number of patients from different patient categories, ” the researchers write in their study, which has not yet been peer-reviewed and is online published. as pre-print.
“Our data show a clear relationship between age and SARS-CoV-2 viral load, with children (less than 12 years old) showing lower viral loads independent of gender and symptom duration.”
More than 2,500 of the people tested were under the age of 20 and 238 of them were under the age of 12, which corresponds to elementary school age.
One metric used to quantify viral load is Cp, which indicates how many PCR cycles – which replicate and amplify genetic material – are required before the virus can be detected.
The higher the number, the lower the viral load, as it indicates how many amplification cycles were required.
In the study, the researchers note that the difference between the mean Cp figure for people over 80 and under 12 is more than four cycles, which corresponds to a 16-fold increase.
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“The most remarkable finding of this study was the relationship between SARS-CoV-2 viral load and age, with significantly lower viral loads in children,” add the authors of the study from Kennemerland in the north of the Netherlands.
“Because previous studies have suggested that young children play a limited role in SARS-CoV-2 transmission, our data supports this suggestion.”
During the pandemic, there has been a mystery as to why children are relatively little affected by Covid-19, while adults are so severely affected.
Children caused far fewer cases during the coronavirus pandemic than other respiratory illnesses, including the flu.
The leading theory for this is due to how the coronavirus enters human cells, through a receptor called ACE2 found on many cells in the upper respiratory tract.
As a result, Professor Wendy Barclay of Imperial College London, a member of NERVTAG, explained last month that this made adults ‘easy goals’ compared to children.
This is because the amount of ACE2 that a person naturally and steadily expresses increases over time, with young children having very few people.
ACE2 is the receptor on the surface of human cells that the coronavirus hijacks and uses to infect.
The Dutch researchers point out that antigen tests, which are faster but not as reliable as PCR tests, are even less accurate when used by an infected patient with a low viral load.
In infected children under 12 years of age, the recorded viral load was less than 30 in nearly a third (31.1 percent) of the cases, almost double the number of people with this low value in all other age groups.
As a result, the researchers say that “SARS-CoV-2 antigen tests may have lower sensitivity in children than adults.”