Covid-19: what do you know based on scientific data?


What is the SARS-CoV-2?

SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), is a positive-strand RNA virus [1], that causes the disease COVID-19. The structural and biochemical comparisons of SARS-CoV-2 led to the scientists to conclude that this virus appears to be optimized to bind to the ACE2 receptor (angiotensin converting enzyme 2 receptor), and this binding is responsible for the virus internalization into the cells [1, 2]. ACE2 is responsible physiologically for maturation of angiotensin, a peptide hormone that controls vasoconstriction and blood pressure [3], and it is expressed in the cell membrane of lung, heart, kidney and intestine tissues [3,4].


How long is the virus able to maintain its stability?

It was recently published in the New England Journal of Medicine a scientific paper where the authors show that SARS-CoV-2 is more stable in plastic and stainless steel than in copper and cardboard [5]. In this study they applied SARS-CoV-2 using aerosols (with a controlled viral load) into the different materials, and left those materials between 21 – 23 ºC and 40% humidity for 7 days.


Figure 1. Stability of SARS-CoV-2 and SARS-CoV-1 in different materials. Adapted from [5]


More precisely, what they observe is that:

  • copper: no viable SARS-CoV-2 was detected after 4 hours
  • cardboard: no viable SARS-CoV-2 was detected after 24 hours (1 day)
  • stainless steel: no viable SARS-CoV-2 was detected after 48 hours (2 days)
  • plastic: no viable SARS-CoV-2 was detected after 72 hours (3 days)

Importantly, this means that before the timings described for each material, although the loads of virus were decreased in comparison to the initial virus loads, they were still detected.

On this study, they also compared the stability between SARS-CoV-2 (red curve in Figure 1) and the previous closest coronavirus known, SARS-CoV-1 (blue curve in Figure 1). The results show that stability between the two virus is actually similar, suggesting that the epidemiologic problem that we are facing with SARS-CoV-2 is not only related with its stability (although is one of the important factors), but can be also due to other factors, raising two hypotheses:

  • high viral loads of virus in the superior respiratory tract
  • the high potential of infected people with SARS-CoV-2 to transmit the virus while they are asymptomatic or with mild symptoms (which are not taken at that time as illness)


Which symptoms does SARS-CoV-2 trigger?


Figure 2. Symptoms and Maximum Body Temperatures According to Day of Illness and Day of Hospitalization of the first case of   Covid-19 reported in United States patient. Adapted from [6]


In the same journal, it was recently published the case study of the first SARS-CoV-2 reported in United States patient (Figure 2). In this report they describe the identification, diagnosis, clinic course, and treatment, including the mild symptoms described initially by the patient and the progression of symptoms to pneumonia at day 9 of the disease [6].


Figure 3. Symptoms of positive SARS-CoV-2 patients in Portugal gathered by local Portuguese authorities. Source: [consulted on March 19th, 2020]


In Portugal, local authorities have been gathering the symptoms that each positive SARS-CoV-2 patient has experienced (Figure 3) [7]. As we can see in Figure 3, majority of positive patients describe dry cough as a symptom, while fever is only the second symptom described.  As described by WHO (Word health Organization) around 80% of people recover from the disease without the need of a special treatment [8]. Nevertheless, WHO describe as high-risk groups older people and people with other health issues such as high blood pressure, heart problems or diabetes, are more likely to develop serious illness [8].


Can asymptomatic people transmit SARS-CoV-2?


Figure 4. Timeline of exposure of different people until they show symptoms and test positive to SARS-CoV-2 (described in the graph as Positive PCR). Adapted from [9].


In Figure 4 it is described a case report of a transmission line in Germany. An individual that went from China to Germany, where he attended business meetings and only after returning to China start feeling the first symptoms. Important to notice that patient 1 only describes symptoms days later after the meeting with Patient 0. In addition, patient 1 was a transmission individual to patient 3 and 4, that only contacted with patient 1, and again only show symptoms days after those contacts. Interestingly, another case report shows that asymptomatic patient can already test positive for SARS-CoV-2  (Figure 5). These studies show that although no symptom was described by these individuals, they were able to transmit SARS-CoV-2  to other individuals. This is why the decrease of social contact is so crucial to decrease the spreading.


Figure 5. Follow up of people who boarded an evacuation flight from Wuhan, China, to Singapore. Adapted from [10].


What is this “let’s flatten the curve” and why #staythefuckhome is so important?

As many specialists have come to public to explain, flattening the curve means reduce the number of cases at a time – allowing our hospitals to be able to take care of the urgent cases without overloading them (Figure 6). Why is this important? If we get the same number of cases but during a longer period, we will reduce the number of patients in critical condition at the same time – which means, we will have not only professionals but also equipment available for these critical cases.


Figure 6. Flatten the curve graph


Is SARS-CoV-2 a laboratory made virus?

Comparative genomic data of SARS-CoV-2 with other coronavirus show that Covid-19 is NOT laboratory manipulated virus [11]. SARS-CoV-2 is approximately 80% similar with SARS-CoV-1 and 96 % similar to bat coronavirus (BatCoVRaTG13) [1].


Which trustworthy websites should I read to know more about SARS-CoV-2?














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