COVID-19, which is caused by the new coronavirus, has been dominating the news lately. However, you may have first become familiar with the term coronavirus during the severe acute respiratory syndrome (SARS) outbreak in 2003.

Both COVID-19 and SARS are caused by coronaviruses. The virus that causes SARS is known as SARS-CoV, while the virus that causes COVID-19 is known as SARS-CoV-2. There are also other types of human coronaviruses.

Despite their similar name, there are several differences between the coronaviruses that cause COVID-19 and SARS. Keep reading as we explore coronaviruses and how they compare to each other.

Coronaviruses are a very diverse family of viruses. They have a large host range, which includes humans. However, the greatest amount of coronavirus diversity is seen in bats.

Coronaviruses have spiky projections on their surface that look like crowns. Corona means “crown” in Latin — and that’s how this family of viruses got their name.

Most of the time, human coronaviruses cause mild respiratory illnesses like the common cold. In fact, four types of human coronaviruses cause 10 to 30 percent of upper respiratory tract infections in adults.

A new type of coronavirus can emerge when an animal coronavirus develops the ability to transmit a disease to humans. When germs are transmitted from an animal to a human, it’s called zoonotic transmission.

Coronaviruses that make the jump to human hosts can cause serious illness. This can be due to a variety of factors, particularly humans’ lack of immunity to the new virus. Here are some examples of such coronaviruses:

  • SARS-CoV, the virus that caused SARS, which was first identified in 2003
  • MERS-CoV, the virus that caused Middle East respiratory syndrome (MERS), which was first identified in 2012
  • SARS-CoV-2, the virus that causes COVID-19, which was first identified in 2019

SARS is the name of the respiratory illness that’s caused by SARS-CoV. The acronym SARS stands for severe acute respiratory syndrome.

The global SARS outbreak lasted from late 2002 to mid-2003. During this time, over 8,000 people were sickened and 774 people died.

The origin of SARS-CoV is thought to be bats. It’s believed that the virus passed from bats to an intermediate animal host, the civet cat, before jumping to humans.

Fever is one of the first symptoms of SARS. This may be accompanied by other symptoms, such as:

Respiratory symptoms can worsen, leading to shortness of breath. Serious cases rapidly progress, leading to pneumonia or respiratory distress.

COVID-19 and SARS are similar in many ways. For example, both:

  • are respiratory illnesses caused by coronaviruses
  • are believed to have originated in bats, jumping to humans via an intermediate animal host
  • are spread by respiratory droplets produced when a person with the virus coughs or sneezes, or by contact with contaminated objects or surfaces
  • have similar stability in the air and on various surfaces
  • can lead to potentially serious illness, sometimes requiring oxygen or mechanical ventilation
  • can have worsening symptoms later on in the illness
  • have similar at-risk groups, such as older adults and those with underlying health conditions
  • have no specific treatments or vaccines

However, the two illnesses and the viruses that cause them are also different in several important ways. Let’s take a closer look.

Overall, the symptoms of COVID-19 and SARS are similar. But there are some subtle differences.

SymptomsCOVID-19SARS
Common symptomsfever,
cough,
fatigue,
shortness of breath		fever,
cough,
malaise,
body aches and pains,
headache,
shortness of breath
Less common symptomsrunny or stuffy nose,
headache,
muscle aches and pains,
sore throat,
nausea,
diarrhea,
chills (with or without repeated shaking),
loss of taste,
loss of smell		diarrhea,
chills

It’s estimated that 20 percent of people with COVID-19 will need to be hospitalized for treatment. A smaller percentage of this group will need mechanical ventilation.

SARS cases were more severe, in general. It’s estimated that 20 to 30 percent of people with SARS required mechanical ventilation.

Estimates of the mortality rate of COVID-19 vary greatly depending on factors like location and the characteristics of a population. Generally speaking, mortality rates for COVID-19 have been estimated to range between 0.25 and 3 percent.

SARS is much more deadly than COVID-19. The estimated mortality rate is about 10 percent.

COVID-19 appears to transmit more easily than SARS. One possible explanation is that the amount of virus, or viral load, appears to be highest in the nose and throat of people with COVID-19 shortly after symptoms develop.

This is in contrast to SARS, in which viral loads peaked much later in the illness. This indicates that people with COVID-19 may be transmitting the virus earlier in the course of the infection, just as their symptoms are developing, but before they begin to worsen.

According to the Centers for Disease Control and Prevention (CDC), some research suggests that COVID-19 can be spread by people who aren’t showing symptoms.

Another difference between the two illnesses is the fact that there haven’t been any reported cases of SARS transmission before symptom development.

A recent study of the complete genetic information (genome) of SARS-CoV-2 samples found that the virus was more closely related to bat coronaviruses than the SARS virus. The new coronavirus has a 79 percent genetic similarity to the SARS virus.

The receptor binding site of SARS-CoV-2 was also compared to other coronaviruses. Remember that to enter a cell, a virus needs to interact with proteins on the cell’s surface (receptors). The virus does this via proteins on its own surface.

When the protein sequence of the SARS-CoV-2 receptor binding site was analyzed, an interesting result was found. While SARS-CoV-2 is overall more similar to bat coronaviruses, the receptor binding site was more similar to SARS-CoV.

Studies are underway to see how the new coronavirus binds to and enters cells in comparison to the SARS virus. Results have so far been varied. It’s also important to note that the research below was performed only with proteins and not in the context of an entire virus.

A recent study has confirmed that both SARS-CoV-2 and SARS-CoV use the same host cell receptor. It also found that, for both viruses, the viral proteins used for host cell entry bind to the receptor with the same tightness (affinity).

Another recent study compared the specific area of the viral protein that’s responsible for binding to the host cell receptor. It observed that the receptor binding site of SARS-CoV-2 binds to the host cell receptor with a higher affinity than that of SARS-CoV.

If the new coronavirus indeed has a higher binding affinity for its host cell receptor, this could also explain why it appears to spread more easily than the SARS virus.

There have been no global SARS outbreaks since 2003. The last reported cases were in 2004 and were acquired in a lab. There have been no more cases reported since then.

SARS has been successfully contained using public health measures, such as:

Will implementing the same measures help COVID-19 go away? In this case, it may be more difficult.

Some factors that may contribute to COVID-19 being around for longer include the following:

  • About 80 percent of people with COVID-19 have a mild illness. Some may not even know that they’re sick. This makes it harder to determine who’s infected and who’s not.
  • People with COVID-19 appear to shed the virus earlier in the course of their infection than people with SARS. This makes it more difficult to detect who has the virus and isolate them before they spread it to others.
  • COVID-19 is now spreading easily within communities. This was not the case with SARS, which was more commonly spread in healthcare settings.
  • We’re even more globally connected than we were in 2003, making it easier for COVID-19 to spread between regions and countries.

Some viruses, such as the flu and the common cold, follow seasonal patterns. Because of this, there’s the question as to whether COVID-19 will go away as the weather becomes warmer. It’s unclear if this will happen.

COVID-19 and SARS are both caused by coronaviruses. The viruses that cause these illnesses likely originated in animals before they were transmitted to humans by an intermediate host.

There are many similarities between COVID-19 and SARS. However, there are also important differences. COVID-19 cases can range from mild to severe, while SARS cases, in general, were more severe. But COVID-19 spreads more easily. There are also some differences in the symptoms between the two illnesses.

There hasn’t been a documented case of SARS since 2004, as strict public health measures were implemented to contain its spread. COVID-19 may be more challenging to contain because the virus that causes this disease spreads more easily and often causes mild symptoms.