Difference Between Coronavirus Disease (COVID-19) And Severe Acute Respiratory Syndrome (SARS)

Coronaviruses are a family of viruses that cause illnesses in animals and humans. They can cause infections ranging from the common cold to severe respiratory infections,which can be fatal. Here, we will look into the details of the difference between the novel coronavirus disease (COVID-19) and Severe Acute Respiratory Syndrome(SARS) and the features of each of these infections.

Coronaviruses are known to occur in animals and some of these viruses can sometimes get transmitted to humans, as well. It is called a spillover event.¹ Such spread of pathogens from animals to humans is called zoonotic transmission.

While 7 coronaviruses are known to cause infection in humans, four of them usually cause symptoms of a common cold. In some rare cases, there may be lower respiratory infections, particularly affecting the younger or older age groups and immunocompromised persons.²

The other three types of coronaviruses result in severe respiratory infectionsthan the other coronaviruses. These include Severe Acute Respiratory Syndrome (SARS),Middle East Respiratory Syndrome (MERS), the outbreaks of which have occurred in the past and the novel coronavirus COVID-19, which is causing the recent infections across many countries since December 2019.

While these three types belong to the same family, they have certain differences, which decides the disease they produce.

• Severe Acute Respiratory Syndrome or SARS was caused by coronavirusnamed SARS-CoV, which was identified in 2002.
• Middle East Respiratory Syndrome or MERS, was caused by coronavirusnamed MERS-CoV, identified in 2012, first reported in Saudi Arabia, which then spread to other countries including the United States (US).³
• The novel coronavirus disease or COVID-19 is caused by coronavirusnamed SARS-CoV2, which was identified in 2019, then began in Wuhan, in China.²

However, the novel coronavirus, COVID -19 is more virulent and potentially fatal, resulting in a pandemic. The novel coronavirus is presently in the news due to the increasing number of infections and deaths due to its complications, affecting several countries across the globe.

Coming to the difference between coronavirus disease (COVID-19) and SARS, we need to understand both the infections in detail. In both the diseases, the causative agents are coronaviruses, however, they differ in their types, their actions and so the diseases they produce are different.

SARS is Severe Acute Respiratory Syndrome, a viral respiratory illness caused by coronavirus – SARS-CoV. It was first reported in Asia in February 2003, but cases were tracked to November 2002. It spread to more than two dozen countries in Asia, Europe, North America, and South America, before it was contained.⁴ Around 8098 people worldwide became sick due to SARS and about 774 of them died.⁴ However, in the United States, it mostly affected people who had traveled to SARS affected countries and did not spread more widely in the community. Since 2004, no cases of SARS have been reported.

Studies suggest that SARS pandemic may have originated from bats, possibly with palm civet as an intermediate host.⁵

The symptoms of SARS include high fever, headache, body ache and a general feeling of malaise. Some may experience mild respiratory symptoms while 10% to 20% may also have diarrhea. A dry cough is often seen after 2 to 7 days and most patients later develop pneumonia. The spread of SARS is mainly through person-to-person contact. Transmission occurs through droplet spread when an infected person sneezes or coughs or on touching surfaces that are contaminated by infectious droplets. It can also have airborne spread, where the virus may spread broadly through the air.⁴

COVID-19 is an acute, sometimes severe, respiratory illness caused by a novel coronavirus SARS-CoV2. It emerged in Wuhan, China in December 2019 and currently spread to more than 70 countries resulting in a pandemic. Similar to the earlier coronavirus infections, the COVID-19 virus too is believed to be originated from the bats. Studies suggest that bats are the most likely reservoir of SARS-CoV2 as it is very similar to bat coronavirus. However, as there are no documented cases of a bat to human transmission, there is a possibility of an intermediate host.⁶ Various studies are being conducted to understand the possible involvement of animals as an intermediate host, some of which can be pangolins, snake or other animals in the wet markets.

Most people affected by COVID-19 have symptoms of mild to moderate respiratory illness. Older people and those with underlying complications like cardiovascular disease, diabetes, respiratory disease, and cancer are more likely to develop severe illness.7

Both COVID-19 and SARS are caused by coronaviruses and result in respiratory diseases in human beings. They are considered to have originated from bats and transmitted to humans through an intermediate host. The infection spreads through the droplets, when an infected person sneezes, coughs or spits and contact with surfaces contaminated with such droplets are seen in both. Both infections begin with mild symptoms but can lead to severe respiratory complications later. The most commonly affected people or those experiencing complications are the elderly people and those with underlying medical conditions.

While these are the common similarities between the two, the difference between coronavirus disease and SARS can be made based on the following criteria.

Based on the symptoms, we can understand some of the differences between coronavirus disease and SARS.

COVID-19 Symptoms – The incubation period is estimated to range from 2 to 14 days, although some variations may be noted. The commonest symptoms of COVID-19 include fever, cough, tiredness, and shortness of breath. Some patients may have body ache, nasal congestion or stuffy nose, runny nose, sore throat or diarrhea.

• There is a possibility that some people get infected with the COVID-19 virus and do not show any symptoms or do not feel unwell.
• About 80% of people recover without requiring special treatment.
• However, one in six patients of COVID-19 can become seriously ill and experience breathing difficulty, needing additional treatment and assistance.⁸
• The emergency or warning signs of COVID-19 include breathing difficulty, chest pain or pressure in the chest, confusion or inability to arouse, bluish lips and face.⁹

SARS Symptoms – The incubation period of SARS ranged between 1 to 14 days., with a mean of 4 to 6 days. The symptoms of SARS usually begin with flu-like symptoms that include fever, chills, headache, malaise and sometimes diarrhea. After a week, fever, dry cough, and difficulty in breathing may be noted. Sometimes, it can worsen the condition and cause a severe respiratory illness that needs special treatment.

Older adults and people who have severe underlying medical conditions like heart or lung disease or diabetes are at great risk of developing serious complications of COIVD-19 illness.⁹

Case fatality risk of about 0.25%-3.0% must be estimated for COVID-19. While higher values may be seen in resource-poor settings with constrained quality of hospital and intensive care q. Higher values of case fatality risk may also be seen in high-income countries with limited surge capacity due to the peak of local epidemics. As the disease continues to spread globally, more work on statistics is going on, which can further clarify the case-fatality risk.¹⁰ The types and number of people getting affected due to COVID-19 vary, depending on the location, population features, and other environmental factors apart from the person’s health condition. However, it is seen that the virulence and spread of COVID-19 are much more than mortality.

The severity of SARS showed higher fatality rates in older patients and those with medical comorbidities. About% 20 to 30% required mechanical ventilation and 10%died due to the disease complications.¹¹ SARS was considered more deadly but was limited to lesser countries and the mortality rate was higher as compared to the number of cases detected.

Transmission, risk of spread, presence of symptoms and the possibility of being infectious are some of the factors to be considered for the difference between Coronavirus disease and SARS.

The transmission of the COVID-19 virus is through droplet infection. The disease spreads from person to person, when an infected person coughs or exhales droplets. The droplets can land on a person’s hand, objects and surfaces like doorknobs, counters, handles or anything that is commonly touched by people. When the person touches these surfaces or if it lands on your hand, the droplet with the virus is transferred to the hand. Further, when the person touches eyes, nose, and mouth with the hand, it can reach the mucus membranes and infect the person. COVID-19 can also spread by breathing the droplets released into the air when an infected person coughs or sneezes.⁸ This can be spread up to 1metre, hence it is advised to practice social distancing to prevent the spread of COVID-19. However, as studies continue, it is considered that droplets can reach far away, more than 1 to 2 meters or even more when coughing or sneezing. This means people will have to be more cautious about keeping more distance between them and wearing protection like masks to avoid infections.

SARS spreads by close person-to-person contact. Close contact means those people living with the patient, caregivers or those in direct contact of the respiratory secretions or body fluids of the infected person. Droplet spread can occur when the infected droplets are propelled at a short distance of up to 1 meter. These can infect another person directly or land on surfaces, which are touched by other people and spread when they touch their nose, mouth, and eyes, thus spreading the infection. The spread is more in people coming in close contact with the patient.

• A difference between coronavirus disease and SARS could be that the spread of COVID-19 may be more worrisome than the earlier coronaviruses. While the research continues, one of the possibilities is that the viral load is the highest in the nose and throat right from the beginning of the infection, whereas, it occurs later in the case of SARS.
• It is necessary to understand the onset and duration of viral shedding and the period of infectiousness of COVID-19. Although it is still unclear, SARS-CoV-2 RNA can be detectable in upper and lower respiratory tracts for weeks after the illness onset. While this is similar to SARS-CoV, in the case of COVID-19 there is a chance of having infections in patients without any symptoms and still tested negative. Cases of COVID-19 have shown asymptomatic infections(the virus is detected without any symptoms) or pre-symptomatic infections (where the virus is detected before the appearance of symptoms).¹²
• Another difference between Coronavirus disease and SARS is the possibility of patients being asymptomatic and the possibility of transmission before the infection is symptomatic. This not only increases the chance of spread, if infectious but also the risk that the patient is not tested for diagnosis and treatment, thus increasing the risk of complications.

Although the basic method of transmission, symptoms, respiratory illness and complications appear similar in COVID-19 and SARS, the genomic characteristics or the molecular factors are different. The difference between coronavirus disease and SARS can be based on molecular factors.

The bronchoalveolar lavage fluid and throat swabs are used to detect the presence of COVID-19 virus RNA. According to a study, the phylogenetic analysis of the COVID-19 virus,sequenced from a sample of nine patients, showed that the virus belongs to the subgenus Sarbecovirus of the genus Betacoronavirus. COVID-19 virusis more similar to two bat-derived coronavirus strains, bat-SL-CoVZC45 and bat-SL-CoVZXC21, than to SARS, which is known as human-infecting coronaviruses.¹³ Thus the main difference between COVID-19 and SARS is that they are genetically distinct. However, the homology modeling revealed that COVID-19 virus had a similar receptor-binding domain structure to that of SARS-CoV, despite amino acid variation at some key residues, as reported by this study.¹³

Another difference between coronavirus disease and SARS is related to the receptor-binding domain (RBD). A study suggested that CoV Spike (S) protein is crucial in viral attachment, fusion, and entry and acts as a target for the development of antibodies, entry inhibitors, and vaccines. This describes the ability of the viral protein to bind with the host cell receptor, which increases the likelihood of its spread and infectious nature.

It was noted that the receptor-binding domain (RBD) in SARS-CoV-2 S protein strongly bound to human and bat angiotensin-converting enzyme 2 (ACE2) receptors. The difference between COVID-19 and SARS is that the SARS-CoV-2 RBD showed significantly greater binding affinity to ACE2 receptors as compared to the SARS-CoV RBD related to SARS.¹⁴ This could explain the present observation that the novel COVID-19 virus spreads easily and faster than the SARS virus, affecting numerous people around the world.

While it is true that both COVID-19 and SARS belong to the family of coronavirus, there are variations in some of their presentation, spread, and genomic features. However, SARS has been contained effectively and there are no known cases since then. The possibility of COVID-19 being more mutant and virulent cannot be ruled out. Also, the chances of people having COVID-19 infection, without any symptoms makes it even more challenging. Also, as the infectious nature of this novel infection can transmit the virus even before it is detected makes it more alarming.

The difference between Coronavirus disease and SARS can help in understanding the ways to control the spread of the novel coronavirus disease and take appropriate action. As there are no vaccines available at the moment for COVID-19, preventing the disease is the only way out. Social distancing, hand washing and wearing protective equipment can hopefully prove beneficial in containing the novel infection.

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