More scientific reasons why children are largely sheltered from Covid-19

  • Several studies have shown that children are less affected by severe Covid-19 than adults
  • Research by UTHealth and the Baylor College of Medicine sheds further light on these protection mechanisms
  • The team has now moved on to analyse blood samples from patients in different stages of the disease 

Children have been shown to be more resilient against Covid-19, the disease caused by SARS-CoV-2, and emerging research has been shedding light on why this is the case. Among the ongoing research is a study that found differences between the lung physiology and immune function of children and adults.

The study was done by researchers from the University of Texas Health Science Center at Houston (UTHealth) and Baylor College of Medicine, and was published in the journal American Journal of Physiology-Lung Cellular and Molecular Physiology.

The findings resulted from a collaboration between paediatric and adult physicians, as well as experts in paediatric surgery, adult critical care, neonatology, and molecular biology.

Low percentage of positive cases among patients under 18

In their paper, the researchers note that in the first 149 082 positive Covid-19 cases in the US, a low 1.7% of cases were infants, children and adolescents under the age of 18. Three paediatric deaths were identified by the Centers for Disease Control and Prevention (CDC) as of April 2020.

The role of ACE2 in protecting children

For a number of months, researchers studying the virus have found a pivotal link between Angiotensin-converting enzyme 2s, called ACE2, and SARS-CoV-2. ACE2 are the receptors (or doors) that allow the virus to enter the body’s cells. What's interesting is that children naturally present with less ACE2 in their lungs than adults.

"ACE2 are important for viral entry and there seems to be less of them in children, because they increase with age," said Matthew Harting, assistant professor in the Department of Pediatric Surgery at McGovern Medical School at UTHealth and senior author of the paper. 

Immune system also plays a role

In addition to the above, the researchers also explained that children’s immune systems respond differently to viruses than those of adults. In essence, this leaves a smaller chance for severe illness in paediatric patients.

Various mechanisms explain these differences, such as the retention of T-cells in children, which have the ability to fight off or limit inflammation. T-cells have a viral response and also an immune modulator response.

“In severe cases of adult Covid-19 patients, we've seen that those T-cells are reduced, so the ability to fight the virus is also reduced. In kids, those T-cells seem to be maintained, so they are still able to prevent the virus," said Harry Karmouty-Quintana, an assistant professor in the Department of Biochemistry and Molecular Biology at McGovern Medical School, and co-author of the paper.

Karmouty-Quintana commented that patients with higher levels of T-cells have higher levels of Interleukin 10 (IL-10) (also known as human cytokine synthesis inhibitory factor), which is an anti-inflammatory cytokine. Children also have a higher concentration of regulator T-cells in their lung tissue.

"IL-10 inhibits the inflammation of other components like IL-6 that are detrimental. Adults tend to experience hyperinflammatory states, where kids do not. In preclinical studies in mice, IL-10 has also shown to decrease with age," explained Karmouty-Quintana.

Lung

Image: Krithika Lingappan, MBBS; Matthew Harting, MD; Bindu Akkanti, MD

Harting stressed the importance of collaborations such as this study because they can shed critical insight into why the disease behaves differently in children compared to older people.

"Even now, as we're learning about effective treatments, we're seeing younger people handle this disease better than older people. Moving forward, physicians and scientists need multidisciplinary collaboration to continue learning. This is just another step in the right direction to attack this virus."

A new study by the same team is underway, using blood samples from patients in different stages of Covid-19. This will help them to understand the disparities in disease progression between children and adults and work towards a possible treatment in the future.

Read more on: coronavirus

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