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Last updated September 11, 2021. 6 minute read

COVID-19 vs. SARS vs. MERS: how are they different?

COVID-19, SARS, and MERS all originated from animals—COVID-19 from bats, SARS from palm civets, and MERS from dromedary camels. While COVID-19, SARS, and MERS are all transmitted person-to-person by respiratory droplets, COVID-19 seems to spread faster but has a lower fatality case rate than SARS or MERS.

Dr Chimene Richa Md Written by Chimene Richa, MD
Reviewed by Mike Bohl, MD, MPH

Coronaviruses (CoVs) are a family of viruses that have an outer crown (or “corona”) of protein spikes when you look at them under an electron microscope. This family causes a range of respiratory illnesses in humans and animals, but only seven coronaviruses affect humans. Four of the seven cause mild respiratory diseases, like the “common cold,” while the other three lead more severe conditions like Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS).


  • Coronaviruses are a family of viruses that cause a range of respiratory illnesses, from the common cold to more severe conditions like coronavirus disease 2019 (COVID-19), severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). 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 and has a lower fatality case rate than SARS or MERS. There is currently no cure for any of these human coronaviruses. Prevention with hand washing, social distancing, and wearing face masks is a key to staying healthy.

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.

COVID-19 vs. SARS vs. MERS


COVID-19, SARS, and MERS are all caused by viruses that used to affect only animals. Because of close contact between humans and animals, the viruses were able to change and “jump” to humans. They can now infect a species (us!) that they could not before. 

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 bat SARS-CoV-2, making them the possible carriers of the virus before it jumped to humans (Anderson, 2020). The human SARS-CoV-2 likely came from close human-animal contact in China and then spread worldwide. 

SARS (severe acute respiratory syndrome) is a viral respiratory disease that was first identified in the Guangdong province of China in February 2003 and then spread to several countries in North America, South America, Europe, and Asia, affecting over 8,000 people (CDC, 2005). Testing suggests that the SARS coronavirus originated in bats and then infected animals called palm civets. These infected palm civets were able to pass the virus on to humans (Anderson, 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) (Anderson, 2020). This illness was first reported in 2012 in Saudi Arabia and remained mainly in countries near and around the Arabian Peninsula (CDC,2019).

Signs & symptoms

Human coronaviruses 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
  • 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.


Who can say what the final public health impact of COVID-19 will be? There are currently hundreds of millions of confirmed COVID-19 cases worldwide with millions of deaths (ArcGIS, 2021). Currently, the United States has the highest total number of confirmed COVID-19 cases. 

These numbers will continue to change as we are still in the middle of the pandemic. Other than the public health impact, COVID-19 has affected many other parts of daily life, including employment, 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, and these from people who had traveled to the affected countries (CDC, 2020). 

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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).


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. This is why you should avoid close contact (being less than 6 feet away) from anyone who might be sick. Wearing a face mask keeps the droplets from traveling, protecting the people around you. While all coronavirus infections are transmitted the same way, they do not do so at the same rate. 

The SARS-CoV-2 infection seems to spread faster than the other two. However, it has a lower case fatality rate of 2.3% as compared to SARS (9.5%) and MERS (34.4%). So COVID-19 occurs in more people but leads to death in fewer cases (Petrosillo, 2020).


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.

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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.


Unfortunately, there is currently no cure for COVID-19, SARS, or MERS, but there are some promising vaccine candidates for COVID-19, two of which have already been approved by the FDA for emergency use. Still, the best defense against these viruses is prevention. 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. That is definitely not going to be the case for COVID-19. 

Scientists around the world are working hard to develop therapies and vaccines to combat these viruses. Usually, vaccines take an average of 10 years to go from lab testing to use in people. However, in light of the global pandemic caused by SARS-Cov-2, new strategies have to be used. The Coalition for Epidemic Preparedness Innovation (CEPI) supports vaccine research for epidemic diseases and promotes the “pandemic paradigm” of vaccine development.

 The “pandemic paradigm” allowed researchers to decrease the time from laboratory vaccine research to clinical trials from the traditional 3–4 years down to 16 weeks (Lurie, 2020). Two COVID-19 vaccines have already been approved by the FDA for emergency use and will be distributed to high-risk individuals before being made available to the general public.


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