More evidence that young children seldom pass on the Covid-19 virus. But another study appears to show this is not true for children older than ten.

Scientists think they have discovered at least one significant reason why children are less likely to transmit Covid-19 and are also less likely to experience the disease anything like as severely as the average adult.

Children produce fewer ‘nasal ACE2 receptors, which serve as the entry point for the virus into cells’, according to an article in the Journal of the American Medical Association. One explanation it provides is that because they have fewer “doorways” allowing the virus to enter the body, the children are less likely to have a viral load that makes them ill or allows them to transmit it to other people. 

Other research has suggested that children get far more common colds per year than adults do, so the body has already built up some antibodies or T-cells to attack the next incoming cold. As colds are also produced by four different types of coronavirus, it is possible that the resistance to the common cold also helps in fighting off Covid-19 or reduces its severity or clears it more quickly, scientists speculate.

A South Korean study shows that younger kids are less likely to transmit and catch COVID-19, while kids ages 10 and older seemingly transmit Covid-19 in the same way and to the same degree as adults. The study is published online in the journal Emerging Infectious Diseases. The basis on which the research was done, however, has severe limitations.

As now is well known, children under 10 years of age were much less likely, the researchers found, to transmit the disease to others.

In the study, the researchers looked at reports for 59,073 contacts of 5,706 coronavirus disease (COVID-19) index patients reported in South Korea between Jan. 20, 2020, when the country reported its first case, through March 27. An index case refers to the first person documented to test positive for the disease in a cluster. There were 10,592 contacts who lived in the same household with the index patients; of those contacts, 11.8% tested positive for COVID-19. Out of the 48,481 non-household contacts, just 1.9% had COVID-19. 

The researchers found that in households with an ‘index patient’ who was between 10 and 19 years old, 18.6% of contacts ended up testing positive for Covid-19.

The problem with the research is that the ‘index patient’, who was the first in the household to test positive for Covid-19, may not actually have been the first person in the household to have absorbed the virus.