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COVID-19 vs. SARS vs. MERS: how do they differ?

Mike Bohl, MD, MPH, ALMchimene richa

Reviewed by Mike Bohl, MD, MPH, ALM, written by Chimene Richa, MD

Last updated: Nov 03, 2021
6 min read


Information about the novel coronavirus (the virus that causes COVID-19) is constantly evolving. We will refresh our novel coronavirus content periodically based on newly published peer-reviewed findings to which we have access. For the most reliable and up-to-date information, please visit the CDC website or the WHO’s advice for the public.

The coronavirus may have only waltzed its way into our consciousness in late 2019, but this family of viruses is actually quite well-known and has been for quite some time. Coronaviruses all have an outer crown (or “corona”) of protein spikes when you look at them under an electron microscope. There are seven types of coronaviruses that affect humans. Four of the seven cause mild respiratory diseases, like the common cold, while the other three lead to more severe conditions like Middle East Respiratory Syndrome (MERS), Severe Acute Respiratory Syndrome (SARS), and COVID-19.

The symptoms of all three illnesses overlap to some extent: fever, cough, shortness of breath. They are all transmitted from person to person by respiratory droplets, but COVID-19 seems to spread faster while having a lower fatality rate than SARS or MERS. The case fatality rate refers to the number of people who die from the infection compared to the number of people who caught it. Since COVID-19 has spread to far more people, more people have died from it than from SARS or MERS, even though those two diseases have much higher case fatality rates.

There is currently no cure for any of these human coronaviruses, though we do have effective vaccines for COVID-19. Coronavirus disease 2019 is an illness caused by a novel coronavirus that was present only in animals prior to 2019. It has led to a pandemic affecting millions of people worldwide. Coronavirus disease 2019 is also called COVID-19—”COVI” for coronavirus, “D” for disease, and “19” because it was discovered in 2019. Let’s dive a little deeper into three of the most severe types of coronavirus diseases: COVID-19, SARS, and MERS.



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COVID-19 (SARS-cov-2) vs. SARS

A lot of the deadliest viruses that ever reached humans started out in the animal population, and coronaviruses are no different. COVID-19, SARS, and MERS, each made the jump from animals to humans, creating a path of destruction along the way. 

The virus that causes COVID-19 is SARS-CoV-2 and appears to have originated in an animal market in the Wuhan province of China. Looking at the DNA of this virus, it is 96% identical to the form of SARS-CoV-2 found in bats, making them the most likely carriers of the virus before it jumped to humans (Andersen, 2020). The human SARS-CoV-2 likely came from close human-animal contact in China and then spread worldwide. 

SARS (severe acute respiratory syndrome) made headlines back in 2003. This viral respiratory disease was first identified in the Guangdong province of China and then spread to several countries in North America, South America, Europe, and Asia, eventually affecting over 8,000 people (CDC, 2005). Testing suggested that the SARS coronavirus also originated in bats and then infected animals called palm civets. These infected palm civets were able to pass the virus on to humans (Andersen, 2020). 

Lastly, dromedary camels are believed to have played a key role in the start of MERS-CoV, the coronavirus that causes Middle East respiratory syndrome (MERS) (Andersen, 2020). This illness was first reported in 2012 in Saudi Arabia and remained mainly in countries near and around the Arabian Peninsula (CDC, 2019).

Symptoms of COVID-19, SARS, and MERS 

Human coronaviruses infection cause respiratory illnesses (think cough, fever, etc.), so it’s no surprise that the clinical characteristics of the different diseases overlap to some extent.

COVID-19 signs/symptoms include (CDC, 2020):

  • Fevers or chills
  • Cough
  • Shortness of breath
  • Fatigue
  • Sore throat
  • New loss of taste or smell
  • Nasal congestion or runny nose
  • Nausea or vomiting
  • Diarrhea

Most people have mild or no symptoms, but some can develop severe illnesses that may require hospital admission to the intensive care unit (ICU). Severe illnesses include acute respiratory failure, acute respiratory distress syndrome (ARDS), pneumonia, and disseminated intravascular coagulation (DIC), among others.

SARS signs/symptoms include (CDC, 2017):

  • Fever
  • Headache
  • An overall feeling of discomfort
  • Body aches
  • Diarrhea (10–20%)

After 2–7 days, people with SARS can develop a cough, and most went on to develop pneumonia.

MERS signs/symptoms include (CDC, 2019):

  • Fevers or chills
  • Cough
  • Shortness of breath
  • Nausea or vomiting
  • Diarrhea

Some people had mild or no symptoms, but many developed pneumonia or kidney failure.

Impact of these illnesses

It may be difficult to know what the extent of the public health impact of COVID-19 will be, but it’s clear that it managed to outpace the infection rate of the other coronaviruses that we’ve seen in the past. SARS capped out around 8,000 cases worldwide while MERS has affected around 2,500 people total since it was first discovered (WHO, 2019).

COVID-19 seems to be more contagious than these other viruses, though thankfully it’s less deadly than the other viruses. Some estimates say that 9.5% of people who catch SARS and 35% of people who catch MERS die of these diseases (Petrosillo, 2020). By comparison, the death rate from COVID-19 varies from place to place but is typically around 2%. Still, since it spreads so easily, far more people have caught COVID-19 and the total number of deaths far exceeds the number of deaths from MERS or SARS combined (Johns Hopkins, 2021).

Beyond the devastating public health impact, COVID-19 has affected many other parts of daily life, including employment, access to education, and the global economy.

During the 2003 SARS outbreak, 8,098 people became ill from SARS around the world, and of these, 774 died. However, according to the Centers for Disease Control and Prevention (CDC), this disease had less of an effect in the United States, with only eight confirmed SARS cases, all among people who had traveled to the affected countries (CDC, 2020). 

The National Institute of Allergy and Infectious Disease (NIAID) reports that there have been no confirmed SARS cases since 2004, likely due to control measures (NIAID, 2020). MERS had even less of a presence in the United States. At the end of November 2019, there were a total of 2,494 MERS cases with 858 associated deaths around the world (with 80% of MERS cases occurring in Saudi Arabia), according to the World Health Organization (WHO, 2019). But, in the U.S., there were only two confirmed MERS cases, both in people who had recently traveled to Saudi Arabia (CDC, 2019).

How coronaviruses are transmitted

The viruses that cause these three human coronavirus diseases (COVID-19, SARS, and MERS) all have person-to-person transmission by respiratory droplets. When you cough, sneeze, or talk, you release tiny droplets of fluid from your nose and mouth. These droplets can hold the coronavirus particles and transmit the virus to others. 

Because of their size, these respiratory droplets cannot travel far—only a few feet. That’s why keeping about six feet of distance from people who aren’t part of your household (and whose vaccination status you’re not sure of) is a good idea. Wearing a face mask keeps the droplets from traveling, protecting the people around you. 

How to prevent coronaviruses

Since COVID-19, SARS, and MERS are all transmitted by respiratory droplets, the best way to prevent infection is to avoid close contact with people who are sick. Close contact means being closer than six feet to the infected person, sharing utensils, kissing or hugging, etc. Washing your hands often with soap and water for at least 20 seconds or using hand sanitizer with at least 60% alcohol can prevent illness by getting rid of any virus particles that may be on your hands.

You should also avoid touching your eyes, nose, and mouth with unwashed hands. Face masks help prevent the infected droplets from traveling to others. Lastly, cover your mouth and nose with a tissue, or the inside of your arm, when you cough or sneeze.

Treatment for coronaviruses

While there is currently no cure for any of these three viruses, vaccines that help prevent the spread of COVID-19 are widely available. SARS and MERS are thankfully well contained at the moment, and much of the effort that went into creating vaccines for these other two viruses actually contributed to the development of the COVID-19 vaccines (Padron-Regalado, 2020). The SARS/MERS outbreaks started and ended too quickly for an effective vaccine to be found—once there was no more need, research in those areas came to a halt. 

There are many other medications still under investigation for the treatment of COVID-19. While some have proven to be ineffective (like ivermectin and hydroxychloroquine), others are quite promising.

Overall, there’s evidence that close contact with certain animals is the greatest risk factor for the development of novel coronaviruses that can spread to humans and cause diseases like COVID-19. Efforts to curb unsanitary animal handling and exotic animal trade have been promoted to reduce this sort of spread in the future (D’Cruze, 2020). 

In the meantime, adhering to public health measures and getting vaccinated are the best ways to control the spread of the current pandemic and reduce the chance of further development of new virus strains.


  1. Andersen, K., Rambaut, A., Lipkin, W., Holmes, E., & Garry, R. (2020). The proximal origin of SARS-CoV-2. Nature Medicine, 26(4), 450-452. doi: 10.1038/s41591-020-0820-9
  2. Centers for Disease Control and Prevention (CDC) – Coronavirus Disease-19 (COVID-19): Symptoms of Coronavirus (2020). Retrieved on Aug 3, 2020 from
  3. Centers for Disease Control and Prevention (CDC) – Middle East Respiratory Syndrome (MERS): About MERS (2019). Retrieved on Aug 3, 2020 from
  4. Centers for Disease Control and Prevention (CDC) – Severe Acute Respiratory Syndrome (SARS): Frequently Asked Questions (2005). Retrieved on Aug 3, 2020 from
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  7. Padron-Regalado E. (2020). Vaccines for SARS-CoV-2: Lessons from Other Coronavirus Strains. Infectious Diseases and Therapy, 9(2), 1–20. Advance online publication. doi: 10.1007s40121-020-00300-x. Retrieved from
  8. Petrosillo, N., Viceconte, G., Ergonul, O., Ippolito, G., & Petersen, E. (2020). COVID-19, SARS and MERS: are they closely related?. Clinical Microbiology And Infection, 26(6), 729-734. doi: 10.1016/j.cmi.2020.03.026. Retrieved from
  9. World Health Organization (WHO): Middle East respiratory syndrome coronavirus (MERS-CoV). (2019). Retrieved Aug 3, 2020, from

Dr. Mike is a licensed physician and the Director, Medical Content & Education at Ro.