Children rarely develop severe coronavirus disease 2019 (COVID-19), the illness that has led to over 102.35 million cases and at least 2.21 million deaths worldwide. Often, older people and those with underlying health conditions or comorbidities are at a higher risk of developing severe COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.
Despite previous studies showing that children often develop a mild illness or exhibit no symptoms at all, it is still unclear why they are spared by the wrath of the viral infection.
Researchers at the Department of Medicine, Northwestern University, and the Ann & Robert H. Lurie Children’s Hospital of Chicago in the U.S. set out to investigate the host response to SARS-CoV-2, respiratory syncytial virus (RSV), and influenza virus (IV) in the nasal mucosa in children and adults.
The study, which appeared on the medRxiv* preprint server, showed that the response to SARS-CoV-2 infection at the primary site of infection is similar between children and adults. However, differences in the immune response to the virus determine disease severity, regardless of the viral load and interferon response at the primary site of infection, which is the nasal mucosa.
Age differences in COVID-19 infection
The coronavirus pandemic, which first emerged in China in December 2019, is more deadly and serious in older adults, those who are immunocompromised, and people with comorbidities. These include hypertension, diabetes, heart disease, kidney failure, and obesity.
Children and teenagers, on the other hand, can still be infected with SARS-CoV-2, but they are usually asymptomatic or with mild symptoms.
Some children, however, can get severely-ill from COVID-19 and may require hospitalization, admission to intensive care, and mechanical ventilation to help them breathe.
Some children who were infected with SARS-CoV-2 develop Multisystem Inflammatory Syndrome in Children (MIS-C). Though the exact cause of MIS-C is still unknown, several cases reported in many countries were tied to COVID-19.
Infants who are less than one year old with underlying medical conditions are more likely to develop severe COVID-19. These conditions include immunosuppression, sickle cell disease, asthma or chronic lung disease, diabetes, genetic, neurologic or metabolic disorders, and obesity.
To arrive at the study findings, the researchers analyzed the clinical outcomes and gene expression in the nasal mucosa in 36 children hospitalized with COVID-19, 24 children with RSV, and 8 children with IV infection. They also studied these in 16 adults with mild to moderate SARS-CoV-2 infection and seven pediatric and 13 healthy adult controls.
Since the study aimed to assess how the host response to SARS-CoV-2 primary site of infection compared between children and adults, they performed ribonucleic acid (RNA) sequencing of nasal mucosa samples obtained from children and adults with COVID-19. They also obtained samples from children with RSV or IV and healthy controls.
The study findings showed that the local antiviral interferon signaling had no differences between COVID-19-positive children and adults and was similar to those with severe RSV.
In summary, the evidence revealed that the response to SARS-CoV-2 infection at the primary site of infection is similar in children and adults. It is also comparable to other respiratory tract viruses.
Hence, the team concluded that local interferon response to SARS-CoV-2 in the upper respiratory tract does not differ between children and adults. The reason behind the differences in symptoms and severity of illness may have been driven by other mechanisms in the body.
The team added that other factors like systemic immune responses and the differences of these responses between children and adults may determine the level of severity of COVID-19 in children and adults.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.