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other beta-coronaviruses, such as those on SARS and MERS, coronaviruses remain viable and infectious on inanimate surfaces such as glass, metal, or plastic from 2 h up to 9 days. Cold and dry conditions increase their virality (43–45); however, future investigations on SARS-CoV-2 are required to provide detailed information. Therefore, the Chinese government disinfects, and even sometimes destroys, cash as part of its attempts to suppress the virus (46). Fortunately, cleaning surfaces with sodium hypochlorite and ethanol or common biocidal substances is a very effective method to inactivate coronavirus within 1 min of exposure (45). To determine the period of optimal infectivity, a clinical study on 17 infected cases found that the nasal viral load peaked within days after the beginning of the clinical signs, indicating that disease transmission to another patient can occur early during infection (47). Incubation Period A large number of people can be infected with SARS-CoV-2 simultaneously. Elderlies suffering from chronic diseases and pregnant women are highly susceptible to the infection (48). The infection varies according to the amount of exposure to the virus and the immune status of the host; a high infection dose of the virus with low immune status will increase the chance of infection and severity of the disease. Based on the report of the first 425 patients in China, the SARS-CoV-2 mean incubation period is 1–14 days, mainly 3–7 days (6). Another study on 1,099 patients reported that the incubation period ranged from 0 to 24 days with an average of 3 days (48). The most recent report based on a study on about 8,866 cases mentioned that the incubation period was 4.8 days (3.0–7.2) (49). Medical authorities must determine the effective quarantine period depending on the most accurate incubation period so that they can prevent infection by the virus during the incubation period (7). Understanding the duration of incubation is also necessary, as it helps health officials to implement more reliable quarantine schemes for critical events. The best present figures for contamination with SARS-CoV-2 range from 2 to 14 days. According to the aforementioned study, a median of 5.2 days incubation time was yielded (6). A later study, which was based on 1,324 cases, suggested a mean of 3 days as the incubation time (48). One study conducted between 20 and 28 January 2020 on 88 cases that traveled to Wuhan showed that the incubation time was between 2.1 and 11.1 days, with an average of 6.4 days (50). Individuals who were exposed to or diagnosed with the virus were typically expected to be quarantined for 14 days. Symptoms, Target Organs, Multiplication, and Body Response to Infection Many coronaviruses, as types 229E, NL63, OC43, and HKU1, can infect humans and induce mild or moderate upper-respiratory problems such as the common cold. Such diseases last for a period, and most people get infected by these coronaviruses at any period of their life. The clinical signs of such illnesses are rhinorrhea, cough, pyrexia, and sore throat, with a common feeling of unwellness. In addition, human coronaviruses may induce lower-respiratory tract diseases such as bronchitis and/or pneumonia (1, 21). However, this is more prevalent in cases with chronic medical problems such as patients with cardiopulmonary disease and immunodeficiency patients, kids, and elderlies. MERS-CoV and SARS-CoV are the two coronaviruses that mainly cause severe diseases. The symptoms of MERS are high body temperature, cough, and difficulty in breathing that ends with pneumonia. Reports mention that out of every 10 MERS-infected patients, 3–4 people died. Cases of MERS primarily occur in the Arabian Peninsula. On the other hand, SARS clinical signs include high body temperature, chills, and body pain, which usually ended by pneumonia—although it is noteworthy that no cases of SARS were found all over the world since 2004 (1, 21). The biochemical associations and pathogenesis of SARS-CoV-2 are definitely similar to SARS-CoV. Both bind to the receptors of angiotensin-converting enzyme-2 (ACE-2) in pneumocytes type II in the lungs, leading to lower respiratory tract inflammation (51). It was clear that binding of SARS spike protein to the ACE-2 receptors resulted in proteolytical processing of complex using (TMPRSS2) type II transmembrane protease leading to the cleavage of ACE-2 and the activation of spike protein (52, 53). This mechanism is similar to that used by viruses of influenza and metapneumovirus in humans, thus promoting the entrance of the virus inside the target cells. It has been suggested that cells, where both ACE-2 and TMPRSS2 are present simultaneously, are more vulnerable to SARS-CoV entry (54). Likewise, early reports mentioned that SARS-CoV-2 infection needs ACE-2 and TMPRSS2 to infect the target cells (2). Viral entry and cell invasion activate the immune response of the infected host and antigen-presenting cells (APCs) begin the inflammatory process. The cycle begins with the APC as they conduct two roles: (1) presenting the viral antigen to CD4+-T-helper (Th1) cells and (2) releasing interleukin-12 to further activate the Th1 cell (21). The Th1 cells stimulate CD8+-T-killer (Tk) cells, which attack any foreign antigen-containing cells. In addition, activated Th1 cells induce B cells to develop antibodies that are specific to the antigens. The frequencies of clinical signs recorded in the first clinical review were as the following percentages: fever, 98%; cough, 76%; and shortness of breath, 55% (3). Many cases showed less severe symptoms for 2–14 days before shortness of breath and severe signs appear. These patients still transmit the infection to whomever they come in contact with during this period and the disease course takes about 8 days. All patients admitted to the hospital suffered from clinical pneumonia, which was confirmed by CT scanning; about 32% of the patients showed hypoxia necessitating ICU admission. In addition, 10% needed ventilation, and two of them needed extracorporeal membrane oxygenation due to refractory hypoxia. The recorded case fatality rate (CFR) was 15%. Most