ACE2, Expression and It's Role of Mortality and Morbidity in Adults, and Children in Upcoming Newer Variants of COVID-19, Pandemic Waves: A Systematic Review and Meta-Analysis

Background: Human coronaviruses can be divided based on their pathogenicity. The types with high pathogenicity including SARS-CoV, MERS-CoV, and the current novel SARS-CoV2. SARS COV2 has led to possibly the worst pandemic of this century in the form of Coronavirus disease 2019 (COVID-19). Initially recognized as a respiratory system disease, COVID-19 has been found to interact with and affect the cardiovascular system leading to myocardial damage and cardiac and endothelial dysfunction mainly via the Angiotensin-converting enzyme5 2 (ACE-2) receptor. In fact, cardiac damage has been noted even without clinical features of respiratory disease. The ACE2 receptors are identified in 72 tissues, ACE2 expression levels were. There are two immune-response phases of COVID-19 disease. Phase 1; occurs during the incubation stage of the disease, during which the adaptive immune system works to eliminate the virus; if any defects occur at this stage, SARS-CoV2 will disseminate and induce systemic organ damage, with more significant destruction of organs with higher expression of ACE2 receptors, including lung, endothelial cells, the heart, and the kidneys. This massive damage leads to Phase 2: severe inflammation in the affected organs. Diabetes, atherosclerosis, and obesity, which are risk factors for cardiovascular disease, down regulate the immune system. These have been associated with a poor prognosis in COVID-19. In addition, some studies have indicated that person-to-person transmission of SARS-CoV-2 can occur by routes outside of the respiratory tract .A study of patients infected with SARS-CoV-2 showed that females were less susceptible to infection than males. Older males with co morbidities were more likely to be infected with SARS-CoV-2. Taken together, these data indicate that: 1) SARS-CoV-2 may infect other human tissues in addition to lungs, and 2) Males may be more susceptible to SARS-CoV-2 infection than females.