One study found that primary children infected with coronavirus have much lower viral loads than adults with Covid-19.
Some scientists believe that the viral load, the amount of virus that a person harbors, is related to increased transmissibility, although there is debate about these claims.
Data from public health officials in the Netherlands reveal a 16-fold difference in the amount of virus between those over 80 and children under 12.
According to the researchers, rapid antigen testing, such as the recommended 15-minute screening used in schools and airports, will also be less accurate for children than for adults because of its lower load.
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This graph shows the Cp value of coronavirus patients by age group. Cp is a measure of how many cycles of PCR analysis, which amplify a genetic signal, are needed to detect a SARS-CoV-2 signal. The higher the number, the lower the viral load. “Median Cp values between the largest population (> 79 years) and the youngest (<12 years) differed in more than 4 PCR cycles, suggesting an approximate 16-fold difference in viral load.", the researchers write
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More than a quarter of a million people in the north of the Netherlands were tested between 1 January 2020 and 1 December 2020.
Of these, 211,933 were performed by qualified healthcare professionals, with viral load data available for 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in a large number of patients from different patient categories.”, the researchers write in their study, which has not yet been peer-reviewed and is published online as a prepress.
“Our data show a clear relationship between age and SARS-CoV-2 viral load, with children (under 12 years of age) having lower viral loads, regardless of sex and duration of symptoms.”.
More than 2,500 of the people tested were under the age of 20 and 238 of these were under the age of 12, equivalent to primary school age.
One metric used to quantify viral load is Cp, which indicates how many cycles of PCR – which replicates and amplifies genetic material – are needed before the virus can be detected.
The higher the figure, the lower the viral load, as it indicates how many amplification cycles were needed.
In the study, the researchers observed that the difference between the average Cp figure for those over 80 and under 12 is more than four cycles, equivalent to a 16-fold increase.
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“The most notable 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 Kennemerland study in the north of the Netherlands.
“As previous studies have suggested that young children play a limited role in the transmission of SARS-CoV-2, our data support this suggestion.”.
Throughout the pandemic there has been mystery surrounding why children are not relatively affected by Covid-19, when adults are so affected.
Throughout the coronavirus pandemic, children have accounted for far fewer cases than in other respiratory illnesses, including the flu.
The main theory of this is due to how the coronavirus enters human cells, through a receptor called ACE2 that is found in many cells of 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 targets” compared to children.
This is because the amount of ACE2 that a person expresses naturally and constantly increases over time, as young children have very little and people.
ACE2 is the receptor on the surface of human cells that the coronavirus sequesters and uses to infect.
Dutch researchers point out that antigen testing, which is faster but not as reliable as PCR testing, is even less accurate when used by an infected patient with a low viral load.
In infected children under 12, the recorded viral load was less than 30 in almost a third (31.1%) of cases, almost double the proportion of people with this low reading in other age groups .
As a result, researchers say that “SARS-CoV-2 antigen testing may have lower sensitivity in children than in adults”.