One study found that primary children infected with coronavirus had much lower viral loads than adults with Covid-19.
Some scientists believe that the viral load – the amount of virus a person has – is linked to increased transmissibility, although there are debates about these claims.
Data from public health officials in the Netherlands show a 16-fold difference in the amount of virus between those over 80 and children under 12.
Rapid antigen tests, such as 15-minute screening used in schools and airports, are also less accurate for children than adults because of their lower 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 the number of cycles of PCR analysis, which amplified a genetic signal, is required to detect a SARS-CoV-2 signal. The higher the number, the lower the viral load. “Mean Cp values between the older population (> 79 years) and the youngest (<12 years) differed by more than 4 cycles of PCR, suggesting a difference of approximately 16 times in viral pregnancy," 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 health 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 the distribution of SARS-CoV-2 viral load in a large number of patients in different categories of patients,” write the researchers in their study, which has not yet been evaluated by colleagues and is published online as pre-print.
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 gender and duration of symptoms.
Over 2,500 of the people tested were under the age of 20 and 238 of them were under the age of 12, the equivalent of primary school age.
A value used to quantify the viral load is Cp, which indicates how many cycles of PCR – which replicates and amplifies the genetic material – are needed 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 found that the difference between the average Cp figure for over 80 years and under 12 years is more than four cycles, equivalent to a 16-fold increase.
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“The most remarkable finding of this study was the relationship between SARS-CoV-2 viral pregnancy and age, with significantly lower viral loads in children,” add the authors of the study in 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 support this suggestion.
Throughout the pandemic, there has been a mystery as to why children are relatively unaffected by Covid-19 when adults are so severely affected.
Children presented with pandemics throughout the coronavirus with far fewer cases than for other respiratory diseases, including influenza.
The main theory for this is due to the way the coronavirus enters human cells, through a receptor called ACE2 that is 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 targets” compared to children.
This is because the amount of ACE2 that a person expresses increases naturally and constantly over time, with very few children having people.
ACE2 is the receptor on the surface of human cells that the coronavirus hijacks and uses to infect.
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 the age of 12, the viral load recorded was less than 30 in almost a third (31.1 percent) of cases, almost double the proportion of people with this low reading in all other age groups. .
As a result, the researchers say that “SARS-CoV-2 antigen tests may have a lower sensitivity in children than in adults.”