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SARS and MERS virus

Severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) are viral infections. Both infections can cause very serious illnesses that particularly affect the lungs.

SARS caused many infections, especially in Asia, in 2002-2004 but was not heard of for some time. A SARS-CoV-2 (COVID-19) outbreak emerged in Wuhan, China in December 2019. This spread rapidly and was declared a global pandemic in 2020.

MERS was first recognised in the Middle East in 2012. Most of the initial infections were in the Middle East. However, by February 2018, the World Health Organization (WHO) had reported cases in many other countries.

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What is severe acute respiratory syndrome (SARS)?

SARS is an infection caused by a virus. The virus belongs to a group of viruses called coronaviruses and is called SARS-CoV. The disease may have started in pigs or ducks in rural South China. The virus may then have changed slightly (mutated) to affect humans.

SARS was first recognised in March 2003 but probably started in China in November 2002. The virus seems to cause an abnormal response in the body's defences (immune response) and this may be a reason for the infection being so serious. The latest novel virus of this group to emerge in late 2019 was SARS-CoV-2, also known as COVID-19. This virus evolves and mutates over time and creates different variants of itself. So far they have been called alpha, beta, gamma, delta and omicron. Each variant has slightly different characteristics and associated symptoms.

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What is Middle East respiratory syndrome (MERS)?

MERS is also a viral infection caused by a coronavirus. The virus that causes MERS is called MERS-CoV. Camels in the Middle East are thought to be the cause of spread to humans. The virus was first recognised in a patient who died from a severe lung illness (respiratory illness) in Saudi Arabia in June 2012.

Most initial cases of MERS occurred in Saudi Arabia and the United Arab Emirates. MERS was subsequently reported in Europe, the USA and Asia.

MERS can vary from not causing any symptoms, to a mild disease, or to a severe illness. WHO has reported nearly 800 deaths.

Note: SARS and MERS are different from bird flu (avian flu), which is caused by an influenza virus. However, SARS or MERS can cause similar symptoms and complications to bird flu.

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How common are SARS and MERS?


The 2002-2003 SARS outbreak affected mostly China, Hong Kong, Singapore and Taiwan. Canada also had a significant outbreak around Toronto. Between March and July 2003, over 8,000 probable cases of SARS were reported from around 30 countries.

SARS-CoV-2 (COVID-19) was designated as a global pandemic by the World Health Organization in 2020 and is thought to have been responsible for approximately 6 million deaths worldwide.


In May 2015, South Korea began investigating an outbreak of MERS. It is the largest known outbreak of MERS outside the Middle East. At the end of July 2015 there had been almost 200 reported cases of MERS in South Korea with 36 reported deaths.

As of February 2018, the WHO has reported over 2,000 cases in 27 countries. In recent times, most cases have occurred in Saudi Arabia. MERS causes death in about 36 out of 100 people.

Symptoms of SARS and MERS

The first symptoms are like flu with:

These symptoms last for 3-7 days.

The second stage affects the lungs and begins three days or more after the start of symptoms. There is a dry cough, usually without any phlegm, fever and breathlessness. The cough varies from mild to severe.

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How do you catch SARS or MERS?


Most cases of SARS appear to have been spread by close contact (within 3 feet) with infected patients. The infection seems to spread in small droplets in the air, which can pass from an infected person. Close contact means:

  • Kissing.

  • Embracing.

  • Any other physical contact with the infected person.

  • Sharing eating or drinking utensils.

  • Conversation less than a metre apart.

Walking past someone or sitting across a waiting room or office for a short time does not risk becoming infected.

Visiting an infected or suspected area, including an airport, within the previous 10 days increases the possibility that any flu-like illness is due to SARS.

Healthcare workers and the families or carers of those who have been infected are at greatest risk of becoming infected.


Transmission of the virus to humans from the dromedary camel is thought to have been the main source of initial infection. Drinking camel milk has been implicated. Once the virus passed into the human population, transmission from one person to another became possible.

The virus is probably passed on by coughing, sneezing and shaking hands. Human-to-human infection is thought to be involved in 50% of cases in Saudi Arabia. Outbreaks within the same hospital have sometimes been reported.

How can spreading SARS or MERS be prevented?

Travel restrictions or screening air travellers for high temperature (fever) may help to prevent the SARS infection being spread. Scanners can detect raised body temperature but can give false results - for example, if a person has sunburn or has been drinking alcohol.

Infected people should be kept away from other people as much as possible, until 10 days after the fever has resolved.

Other people living in the same house should wash their hands frequently with an alcohol-based antiseptic solution. Disposable gloves should be used for any close contact with the infected person.

The patient should wear a mask or at least cover the mouth when coughing.

Towels, bedding and eating utensils should not be shared.

Diagnosing SARS and MERS

If you are thought to have become infected with SARS-CoV-2 you should stay at home and rest. Testing is available if necessary (for instance in hospitals). Admission is not usually required unless you have significant underlying conditions or frailty.

MERS you will be admitted to hospital for tests (investigations). These tests will include blood tests and a chest X-ray. A computerised tomography (CT) scan of your chest may also be needed.

Tests on samples of sputum, urine, stool (faeces) and blood can detect if the virus is present or whether another type of infection is causing your symptoms.

Treatment for SARS and MERS

During the SARS-CoV-2 (COVID-19) pandemic the following general principles for treatment were developed:

  • Mild illness was treated supportively in the community whilst isolating the infected person. Those people at higher risk of developing severe illness because of age or underlying medical conditions were recommended to receive paxlovid or remdesevir antiviral treatments.

  • Moderate illness requiring hospitalisation for intravenous fluids and extra oxygen were also given remdesevir and dexamethasone - either alone or in combination.

  • Severe illness was supported in a high dependency or critical care environment by intubation and ventilation (to help with breathing) and vasopressor medicines to help maintain blood pressure. The patients are usually kept lying on their tummies - clinicians call this 'nursing prone'. The patient will be kept in strict isolation with barrier procedures in place to prevent the spread of infection. If ventilation isn't helping them recover then extra-corporeal membrane oxygenation (ECMO) may be tried. At the same time combinations of other antiviral treatments (baricitinib or tocilizumab) were given with dexamethasone.

After discharge from hospital

The infected person should monitor and record their temperature twice-daily. If the body temperature is raised to 38°C or above on two consecutive occasions, they should inform (by telephone) the hospital where they had been a patient.

Patients should remain at home for seven days after discharge, keeping contact with others to a minimum. This is to reduce the risk of transmission in case the person may still be infectious for a short time after they have recovered from the infection.

Additional home confinement may need to be needed, particularly in patients who have low body defences to infection (immunosuppressed).

What is the outcome (prognosis)?

The World Health Organization estimate the global case-fatality rate for SARS-CoV-2 (COVID-19) is 2.2%, or approximately 1 in every 50 infected people. This is higher than with influenza.

Compared to SARS, MERS appears to kill more people - 20 in every 50 infected people.

The risk of severe infection and death is higher for older people, those with other illnesses (particularly diabetes and cardiovascular disease) and those with poor body defences to infection (immunosuppressed).

SARS-CoV-2 has also been associated with long term health consequences in some known as 'long COVID'. This has several possible symptoms but predominantly fatigue, muscle weakness, sleep difficulties and anxiety.

How can SARS and MERS be prevented?

Effective prevention relies on early detection of people who have become infected in order to prevent the infection from spreading.

Several vaccines have been developed for SARS-CoV-2 (COVID-19) and boosters have also been given.

There is currently no available vaccine for MERS.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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