key: cord-0845403-f2yr9f7e authors: Haileamlak, Abraham title: Why COVID-19 is Less Severe in Pediatric Patients? date: 2020-07-01 journal: Ethiop J Health Sci DOI: 10.4314/ejhs.v30i4.1 sha: eed9239e0a849fb004c9cffe9d3e33592f97a6dc doc_id: 845403 cord_uid: f2yr9f7e nan SARS-CoV-2 is one of seven coronaviruses known to infect humans. Other than SARS-CoV-2, the other coronaviruses causing SARS and MERS are deadly, the rest are relatively benign causing only common colds in the vast majority of cases. SARS-CoV-2 indiscriminately infecting people with varying severity across geographies, genders, and occupations. Despite this indiscriminate attack, experiences and studies indicate that children are mildly affected in comparison to adults, representing approximately 5% of cases and less than 1% of admissions to hospital (1, 2) . The proportion of severe and critical cases was 10.6%, 7.3%, 4.2%, 4.1%, and 3.0% for the age group of ˂1, 1-5, 6-10, 11-15 and >15 years, respectively (1). SARS and MERS showed similar pater where kids are largely spared from severe diseases. Swine flu (H1N1) virus, responsible for the flu pandemic of 2009 and 2010 preferentially had tummy symptoms on children. It became mysterious why children are less sick after being infected where more than 90 percent of pediatric cases presenting as moderate, mild, or without symptoms entirely. "Why most of the children's COVID-19 cases were less severe than adults' cases is puzzling. Scientists and clinicians need to learn more about this virus and the immune response against it at different age groups. Untying the mystery why SARS-CoV-2 is less severe in children could help to design new ways to combat the spread of the disease. Different literatures forwarded the following ideas to explain why children develop mild COVID-19 disease. 1. Vulnerability to ARDS: though small number of cases pass through all phases, COVID-19 disease is having three distinct phases namely the viral phase, the pulmonary phase, and the hyperinflammatory phase. It is during the hyperinflammatory phase cases are likely to develop severe complications like acute respiratory distress syndrome (ARDS). However, studies showed that children are not less prone to developing ARDS during respiratory tract infections; in fact, during the H1N1 flu pandemic, being under the age of one year was a significant risk factor for developing a severe form of ARDS (3, 4) . Therefore, this argument cannot hold true. One of the reasons for the milder COVID-19 disease presentation in children compared to adult may be due to a qualitatively different response to the SARS-CoV2 virus (5 (6) . The presence of other viruses in the airways of children could limit the growth of SARS-CoV2 by direct virusto-virus interactions and competition (7). Similar to that of SARS-CoV-1, SARS-CoV-2 establishes infection by glomming on to a protein called angiotensinconverting enzyme (ACE)2 which is found on the surfaces of cells throughout the body (8) . Differences in the expression levels of the ACE-2 receptor between children and adults could contribute for the less severe disease in children. Some researchers have hypothesized that kids' lung cells could make fewer-or perhaps even differently shaped-ACE2 proteins. This is an example of the fact that the immune systems of children and adults are different, both with respect to their composition and functional responsiveness (9). To note, although children tend to have mild forms of COVID-19, protective measures should be taken to prevent them from becoming infected. This is important for mitigating the pandemic, as not only can children transmit viruses even when presenting mild forms of the disease, but they have been shown to harbour large amounts of the virus even without showing symptoms (10). It is important to remember that viruses can persist in faeces long after they are gone in nasopharyngeal secretions. Understanding the milder COVID-19 disease in children will provide important information about the disease. It may also suggest important protective mechanisms and targets for future therapies. Epidemiology of COVID-19 among children in China Systematic review of COVID-19 in children shows milder cases and a better prognosis than adults Viral Infection in the Development and Progression of Pediatric Acute Respiratory Distress Syndrome. Front Pediatr Influenza A (H1N1) Virus Infection Why is COVID-19 so mild in children? Viral dynamics in mild and severe cases of COVID-19 Virus-virus interactions impact the population dynamics of influenza and the common cold A genome-wide transcriptomic analysis of protein-coding genes in human blood cells McMichael. Evolution of the immune system in humans from infancy to old age.