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STOCKHOLM (Sweden), March 25 (Dialogue) The reasons why children are less likely to be severely ill from COVID than adults are unclear.
Some suggest this may be because children are less likely to develop conditions such as type 2 diabetes and high blood pressure that are known to be associated with more severe COVID. Others think it may be because of differences in children’s ACE2 receptors — the way viruses get into our cells.
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Some scientists have also suggested that children may have higher existing immunity to COVID than adults. In particular, this immunity is thought to come from memory T cells (immune cells that help your body remember invading bacteria and destroy them) produced by the common cold — some of which are caused by coronaviruses.
We put this theory to the test in a recent study. We found that T cells previously activated by the coronavirus that causes the common cold recognized SARS-CoV-2 (the virus that causes COVID) in children. These responses decline with age.
Early in the pandemic, scientists observed the presence of memory T cells capable of recognizing SARS-CoV-2 in people who had never been exposed to the virus. These cells are often called cross-reactive T cells because they arise from past infections caused by pathogens other than SARS-CoV-2. Studies have shown that these cells can provide some protection against COVID and even enhance the response to COVID vaccines.
what did we do
We used blood samples from children, taken at the age of two and then again at the age of six before the pandemic. We also included adults, none of whom had been previously infected with SARS-CoV-2.
In these blood samples, we looked for T cells specific to a coronavirus that causes the common cold, called OC43, as well as T cells that responded to SARS-CoV-2.
We used an advanced technique called high-dimensional flow cytometry that allowed us to identify T cells and characterize their state in great detail. In particular, we investigated T cell reactivity to OC43 and SARS-CoV-2.
We found that the frequency of SARS-CoV-2 cross-reactive T cells was closely related to that of OC43-specific memory T cells, and the frequency was higher in children than in adults. Cross-reactive T-cell responses were evident in two-year-olds, peaked at six, and then declined with age.
We’re not sure if the presence of these T cells translates into protection against COVID, or by how much. But this existing immunity appears to be particularly effective early in life, and it could go some way to explaining why children tend to fare better than adults when they get COVID.
some restrictions
Our study was based on a sample of adults (26-83 years) and children aged 2 and 6 years. We did not analyze samples from children of other age groups, which is important to further understand age differences, especially given that COVID-19 mortality rates are lowest among children aged 5 to 9 and higher among younger children. We also did not have samples from teens or adults under the age of 26.
In addition, our study investigated T cells circulating in the blood. But immune cells are also found in other parts of the body. It remains to be determined whether the age differences observed in our study are similar to samples from lower respiratory tract or tonsil tissue, for example, where SARS-CoV-2-responsive T cells were also detected when exposed to the virus. (dialogue)
(This is an unedited and auto-generated story from a Syndicated News feed, the content body may not have been modified or edited by LatestLY staff)
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