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SJD Barcelona Children's Hospital

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Infection in children
Una niña durante la realización de una PCR en el marco del estudio Kids Corona

Since the onset of the COVID-19 pandemic, different studies have shown that the disease affects pediatric and adult populations differently.

The number of children affected seems to be much lower than that of adults, despite their being a risk group for serious respiratory infections, and when they become infected, they usually suffer from a milder form of the disease. We are joining forces to answer key questions.

Do children catch COVID-19?

Are children infected less often than adults, are they infected just as often but they don’t transmit the disease, or are they infected just as often but do not develop the disease?

To answer this question, we need studies with many patients and in which the samples are collected in a harmonized and standardized way so that we can compare them and extract reliable results.

To this end, we have conducted an ambitious study of adults and children living together in the same family home where there has been a case of COVID-19. Through serological tests, in which we take a blood sample to see if antibodies against the coronavirus are present, we can know if more children or adults have become infected in a home where there has been a case of COVID-19. Using the PCR technique with samples from the back of the nose and throat (also called a nasopharyngeal swab) we can detect if the virus is still present or if it has already been eliminated.

In addition, we have also started a large seroprevalence study with about 2000 children and adolescents that will allow us to know the level of immunity they have developed against COVID-19, taking into account the degree to which they are affected, and study possible protective factors that can explain the differences between children and adults.

Why do children develop the disease more mildly?

There are several factors that may contribute to COVID-19 being milder in children, which we are investigating in several studies.

On the one hand, children have different microbes in the back of the nose and throat (the nasopharynx) to those of adults. During the first years of life, these microbes are very numerous and diverse, and this could act as a protective factor for the disease by hindering the entry or replication of the coronavirus. On the other hand, it is known that the enzyme that converts angiotensin 2 (abbreviated as ACE2), a molecule that is needed for the lungs to work properly, is the preferred receptor for coronavirus, that is, it is the place where the virus attaches itself when it infects a cell.

What is not yet clear is the difference in ACE2 levels and function in children and adults, but because of its key role as a gateway for coronavirus in the cell, it is thought to play a key role in the protection of children against COVID-19. By studying microbes and ACE2 in children and adults, both those affected by COVID-19 to varying degrees and those unaffected, we will answer these questions.

Finally, immunity can also be a protective factor in children. It is believed that their innate immunity (the first line of defense) could be superior to that of adults and would allow for better control of the early stage of the disease. Likewise, adaptive immunity (the more specific defense and that which, in adults, can lead to exaggerated inflammation) could be lower. By studying the immune response in children and adults, both those affected by COVID-19 to varying degrees and those unaffected, we can understand the role played by the immune system of children and adults in the evolution of the disease.

What have we discovered so far with our research? (updated June 8, 2020)

The research team of the Kids Corona platform has visited 411 family homes in which a parent diagnosed with COVID-19 by PCR had been identified.

The preliminary results of the serological tests, in which we take a blood sample to check for antibodies against the coronavirus, showed that 17.5% of the 724 children who lived with a parent who was ill with COVID-19 had also contracted the virus. This is a percentage very similar to that observed in adults who have lived with an infected person (18.9%), so we can conclude that children are infected to a similar extent to adults who come into contact with a case of COVID-19.

However, of the children with COVID-19, more than half had no symptoms and the rest had very mild symptoms, mainly fever, except for one child who required hospital admission.

Therefore, although children become infected with COVID-19 to the same extent as adults, the disease manifests itself in a much milder form in children than in adults.

Study on COVID-19 in homes

Estudio sobre la COVID-19 en hogares

The information we obtain from the studies we have underway will be essential to continue advancing in the prevention, diagnosis and treatment of COVID-19. Understanding how COVID-19 affects children may be key to finding out how the transmission or severity of the infection in adults may be reduced.