All you should know about Coronavirus. High risk or low risk?
Since the first reports of a novel pneumonia (COVID-19) in Wuhan city, Hubei province, China there has been considerable discussion and uncertainty over the origin and the characteristics of the virus, SARS-CoV-2.
The world has plunged into a complete information chaos.
Coronaviruses (CoVs) are a group of viruses that co-infect humans and other vertebrate animals. CoV infections affect the respiratory, gastrointestinal, liver, and central nervous systems of humans, livestock, birds, bats, mice, and many other wild animals. For example, severe acute respiratory syndrome (SARS) in 2002 and the new emerged SARS-CoV-2 in 2019 are both coronaviruses that transmitted from animals to humans. This new virus causes acute lung symptoms, leading to a condition that has been named as “coronavirus disease 2019” (COVID-19). The discovery of SARS-CoV-2 (2019) belongs to a new evolutionary branch within the CoV.
This review summarize the similarities and differences between SARS-CoV-2 (2019) and SARS-CoV (2002), both of which cause major disease outbreaks in China and worldwide, which will provide comprehensive reference to improve public information, to better understand the level of risk and to enhance prevention.
The differences and similarities of clinical characteristics between COVID-19 (2019) and SARS (2002) are summarized in this Table 1:
The Initial events and epidemic development — SARS and COVID-19
SARS. On Nov. 27th, 2002, a respiratory illness erupted in Guangdong Province, China. The following month, there were clusters of atypical pneumonia reported in other parts of mainland China, Hong Kong, Canada, and Singapore. In June, 2003, SARS-CoV spread across 26 countries in six continents, and caused a cumulative 8,096 cases and 774 deaths (9.6%). In particular, a higher mortality (21%) was found in hospital staff.
COVID-19. On Dec. 29th, 2019, the health departments of Hubei Province received a report that four employees of the South China Seafood Wholesale Market were diagnosed with unknown-caused pneumonia in a local hospital, which was the first report of SARS-CoV-2. On Dec. 31st, 2019, the National Health Commission of People Republic of China and Chinese Center for Disease Control and Prevention (China CDC) participated in the investigation and case-searching work. Nowadays, the number of patients infected with SARS-CoV-2 continues to increase worldwide. By the date of this article’s submission, a cumulative 93,455 cases and 3,198 deaths (3.4%) were reported worldwide. In China, the number is 80,270. 65 countries in six continents are reported with cases.
COVID-19 is far more contagious than SARS. It has spread on a great scale and very quickly. The number of infected, in the first two months, has been ten times higher than the whole number of SARS cases in 2003.
(High risk of contagion cause of a very large community of infected)
Will the COVID-19 outbreak burn out in the summer as happened with the SARS epidemic in 2003?
SARS. As shown in Figure 2, SARS could not take the heat. SARS remains stable at 4 degrees Celsius, but will lose its activeness in three days at 37 degrees and can survive for only 15 minutes at 70 degrees Celsius below zero, according to research by Bao Zuoyi and Liu Yongjian at China’s Academy of Military Medical Sciences. During the 2003 SARS outbreak, for every rise of 1 degree Celsius in Hong Kong, the number of confirmed cases declined by 3.6. The SARS outbreak lasted about eight months. Scientists have never discovered a cure for SARS, and it is widely believed the virus dies off during warm weather.
COVID-19. COVID-19 remains stable at 4 degrees Celsius and can survive for several years at 60 degrees below zero, according to the Chinese Center for Disease Control and Prevention. In higher temperatures, its resistance declines, but the temperature affects only the virus’ survival time, not its ability to infect. As temperatures rise, coronavirus floats in the air or attaches to surfaces, both places where it can survive for only a short time. But once in the body, its ability to infect does not decrease.
We expect the number of new cases of COVID-19 to peak in mid March and then decrease. The increase of temperature will make very difficult the virus survival in the environment. The decisive factor to eliminate COVID-19 will be the reduction of new infected.
(High risk of keeping active the number of new infections and of not burning out the virus)
Clinical Symptoms
SARS. The initial symptoms of SARS patients were fever (100%), cough (61.8%), myalgia (48.7%), dyspnea (40.8%), and diarrhea (31.6%), and the prognosis of patients was associated with host characteristics (including age, gender, etc.). During hospitalization, respiratory distress occurred in 90.8% of SARS patients. The duration from disease onset to severe respiratory distress was an average of 9.8 ± 3.0 days.
COVID-19. In comparison, COVID-19 showed similar trends with SARS patients. Fever, fatigue, and dry cough are the main manifestations of the patients, while nasal congestion, runny nose, and other symptoms of the upper respiratory tract are rare. COVID-19 can be classified into light, normal, severe, and critical types based on the severity of the disease: (1) Mild cases — the clinical symptoms were mild, and no pneumonia was found on the chest computed tomography (CT); (2) normal cases — fever, respiratory symptoms, and patients found to have imaging manifestations of pneumonia; (3) severe cases — one of the following three conditions: respiratory distress, respiratory rate ≥ 30 times / min, partial arterial oxygen pressure (PaO2)/oxygen absorption concentration (FiO2) ≤ 300 mmHg; (4) critical cases — one of the following three conditions: respiratory failure and the need for mechanical ventilation, shock, or the associated failure of other organs requiring the intensive care unit. The current clinical data show that the majority of the deaths occurred in the older patients (16%). However, severe cases have been documented in young adults who have unique factors, particularly those with chronic diseases, such as diabetes or hepatitis B. Those with a long-term use of hormones or immunosuppressants, and decreased immune function, are likely to get severely infected.
SARS causes a serious respiratory distress in almost all hospitalized cases in a short time. In most of the cases, COVID-19 shows mild symptoms, (1) (2) as above. The most severe cases (3), occur rarely.
(Moderate risk of severe symptoms)
Virus Incubation
SARS. The incubation period of SARS is 1–4 days. However, in a small number of patients, the incubation period may be longer than 10 days.
COVID-19. It has been demonstrated that the latency of COVID-19 varies from 3–7 days on average, for up to 14 days. During this incubation period, patients are contagious, and it has been reported that each case infected on average 3.77 other people (uncertainty range 2.23–4.82).
By comparison, we found that the average latency of COVID-19 is slightly longer than that of SARS. This is one of the most important factors that increase the risk of virus spread.
(High risk of contagion from asymptomatic infected)
Susceptible Populations
SARS. According to the demographic information of SARS patients, infection occurred in all age groups (the average age was ≦45). There was a proportional difference between male and female (female predominance), with a male-to-female ratio of 1:1.25. In addition, hospital staff had a higher risk due to the proximal interactions with large numbers from the infected population. The mortality caused by SARS increased with age (> 64 years), and the overall mortality rate during the outbreak of SARS was estimated at 9.6%.
COVID-19. Medicine papers reported that people who have not been exposed to SARS-CoV-2 are all susceptible to COVID-19. Among the 79,968 patients who have been confirmed with COVID-19, nearly half of the patients have been aged 50 years or older (47.7%). The male-to-female ratio is about 2.7:1 and the average incubation period is 5.2 days. However, severe COVID-19 cases and deaths have mostly been in the middle-aged adults and the elderly with long smoking histories or other basic diseases, such as heart disease and hypertension. At the time that this article was been submitted, COVID-19 patients mortality rate was 3.4%.
Mortality risk for COVID-19 is 65% lower than SARS.
(Low mortality risk for those who are <65 years old and have no other diseases)
Why is it spreading so quickly?
It’s very interesting to highlight that the genome of SARS-CoV-2 (2019) is more than 85% similar to the genome of the SARS-CoV (2002) virus, indicating the evolutionary similarity between these two CoV-like virus.
SARS. SARS-CoV (2002) has got a spike (S) protein and a N protein that confer stability to the viral particle. Spike (S) protein can bind to the cellular receptors of sensitive cells and mediate infection of their target cells. SARS-CoV (2002) can enter host cells through the interaction between S protein and its host receptor ACE2. The binding of spike S protein to ACE2 and the subsequent downregulation of this receptor contribute to severe alveolar injury during SARS.
COVID-19. SARS-CoV-2 (2019) acts in the same way seen for the SARS-CoV (2002). The receptor binding domain of SARS-CoV-2 (2019) is also capable of binding ACE2 receptors. It uses ACE2 receptors to infect humans, bats, civets, monkeys and swines, but it cannot bind to the cells without ACE2. Compared to previously reported SARS (2002) strains, SARS-CoV-2 (2019) uses ACE2 receptors more efficiently.
SARS-CoV (2002) and SARS-CoV-2 (2019) uses some types of ACE2 receptors to infect cells. These receptors are very widespread in human and even in some animal species cells. Instead, viruses as MERS (2012) and H5N1 (bird flu, 2003) use different and less common receptors. This is one of the reason why they were not so widely diffused.
There are four amino acid variations of spike S protein between SARS-CoV-2 (2019) and SARS-CoV (2002). The mutation of proteins determines two important characteristics of the SARS-CoV-2 (2019): a higher ability to infect but a lower pathogenicity than SARS-CoV (2002). The high affinity between ACE2 and SARS-CoV-2 (2019) S protein also suggested that the population with higher expression of ACE2 might be more susceptible to SARS-CoV-2 (2019). A recent analysis indicated that Asian males may have higher expression of ACE2. The differences in ACE2 variants among different populations suggested that the diverse genetic basis might affect ACE2-virus binding efficiency: Asians have much higher ACE2 expression cell ratio compared to Europeans, Africans and admixed Americans.
